Ecosyste.ms: Awesome

An open API service indexing awesome lists of open source software.

https://github.com/pocorall/scaloid

Scaloid makes your Android code easy to understand and maintain.
https://github.com/pocorall/scaloid

scala

Last synced: about 2 months ago
JSON representation

Scaloid makes your Android code easy to understand and maintain.

Lists

README 

        





# Simpler Android



Scaloid is a library that simplifies your Android code. It makes your code easy to understand and maintain by [leveraging Scala language](https://github.com/pocorall/scaloid/wiki/Appendix#wiki-faqs-about-scaloid).



For example, the code block shown below:



```scala

val button = new Button(context)

button.setText("Greet")

button.setOnClickListener(new OnClickListener() {

  def onClick(v: View) {

    Toast.makeText(context, "Hello!", Toast.LENGTH_SHORT).show()

  }

})

layout.addView(button)

```



is reduced to:



```scala

SButton("Greet", toast("Hello!"))

```



### Benefits

 * **Write elegant Android software**


   Simplicity is number one principle, keeps programmability and type-safety.

 * **Easy to use**


   Check the [quick start guide](https://github.com/pocorall/scaloid/wiki/Installation#wiki-quick-start)

 * **Compatible with your legacy code**


   You can [use both Scaloid and plain-old Java Android API](https://github.com/pocorall/scaloid/wiki/Appendix#wiki-i-cant-use-scaloid-because-it-does-not-provide-a-functionality-x). You can gradually improve your legacy code.

 * **Production quality**


   Not a toy project. The creator of Scaloid uses it to build [a millionth downloaded app](https://play.google.com/store/apps/details?id=com.soundcorset.client.android).



### Demos



Fork one of this to start a new project:

 * [Hello world of Scaloid for sbt](https://github.com/pocorall/hello-scaloid-sbt) (recommended, it builds faster)

 * [Hello world of Scaloid for maven](https://github.com/pocorall/hello-scaloid-maven)

 * [Hello world of Scaloid for gradle](https://github.com/pocorall/hello-scaloid-gradle)



Learn how Scaloid can be used in action:

 * [Scaloid port of apidemos app](https://github.com/pocorall/scaloid-apidemos)

 * [List of projects using Scaloid](https://github.com/pocorall/scaloid/wiki/Appendix#wiki-list-of-projects-using-scaloid)

 * [Tutorial by Gaston Hillar](http://www.drdobbs.com/mobile/developing-android-apps-with-scala-and-s/240161584) - [part 1](http://www.drdobbs.com/mobile/developing-android-apps-with-scala-and-s/240161584) and [part 2](http://www.drdobbs.com/mobile/developing-android-apps-with-scala-and-s/240162204)



## Contents



 * [Core design principle](#core-design-principle)

 * [UI Layout without XML](#ui-layout-without-xml)

   * [Layout context](#layout-context)

   * [Styles for programmers](#styles-for-programmers)

   * [Automatic layout converter](#automatic-layout-converter)

 * [Lifecycle management](#lifecycle-management)

 * [Asynchronous task processing](https://github.com/pocorall/scaloid/wiki/Basics#wiki-asynchronous-task-processing)

 * [Implicit conversions](https://github.com/pocorall/scaloid/wiki/Basics#wiki-implicit-conversions)

   * [Shorter listeners](https://github.com/pocorall/scaloid/wiki/Basics#wiki-enriched-implicit-classes)

   * [Database cursor](http://blog.scaloid.org/2014/02/simple-enhancements-on-accessing.html)

 * [Traits](https://github.com/pocorall/scaloid/wiki/Basics#wiki-traits)

 * [Smarter logging](https://github.com/pocorall/scaloid/wiki/Basics#wiki-logging)

 * [Improved getters/setters](#scala-getters-and-setters)

 * [Classes](#classes)

   * [Concise dialog builder](#class-alertdialogbuilder)

   * [Beauty ArrayAdapter](#class-sarrayadapter)

   * [Dynamically Preferences](#class-preferences)  [`Read in blog`](http://blog.scaloid.org/2013/03/dynamicly-accessing-sharedpreferences.html)

   * [Binding services concisely](#class-localservice)  [`Read in blog`](http://blog.scaloid.org/2013/03/introducing-localservice.html)

   

## Other links   

 * [Quick start guide](https://github.com/pocorall/scaloid/wiki/Installation#wiki-quick-start)

 * [API doc](http://docs.scaloid.org/)

 * [Blog](http://blog.scaloid.org/)

 * [Twitter](https://twitter.com/scaloid/)

 * [FAQs](https://github.com/pocorall/scaloid/wiki/Appendix#wiki-faqs-about-scaloid)

     * [FAQs about Scala on Android](https://github.com/pocorall/scaloid/wiki/Appendix#wiki-faqs-about-scala-on-android)

 * [Inside Scaloid](https://github.com/pocorall/scaloid/wiki/Inside-Scaloid)

 * [We are hiring!](#we-are-hiring)



## Core design principle



"Being practically simple" is number one principle of Scaloid. Most frequently used things should be written shorter, like [Huffman coding](https://en.wikipedia.org/wiki/Huffman_coding). To do this, I first observed Android programs I wrote, and thought that which part of the code is more fundamental than others. For example, what is the most essential part of buttons? Buttons should have some visible things on it, such as title or image, so the buttons are created like this: `SButton("Hello")`. The second essential part is doing something when it is pressed: `SImageButton(R.drawable.hello, toast("World!"))`. What should be the third one? The answer might not the same for every people, but I think that repetition frequency of press-and-hold action is nice: `SButton("Add", n += 1, 500)` increases `n` for every 500 milliseconds when the user holds the button.



## UI Layout without XML




Android SDK leverages XML to build UI layouts. However, XML is considered still a bit verbose, and lacks programmability. Scaloid composes UI layout in Scala DSL style, therefore achieve both clarity and programmability. For example, suppose a legacy XML layout as shown below:



```xml



    

    

    

    

    

    

    

        

        

    



```



is reduced to:



```scala

new SVerticalLayout {

  STextView("Sign in").textSize(24.5.sp).<<.marginBottom(25.dip).>>

  STextView("ID")

  SEditText()

  STextView("Password")

  SEditText() inputType TEXT_PASSWORD

  SButton("Sign in")

  new SLinearLayout {

    SButton("Help")

    SButton("Sign up")

  }.wrap.here

}.padding(20.dip)

```



The layout description shown above is highly programmable. You can easily wire your logic into the layout:



```scala

new SVerticalLayout {

  STextView("Sign in").textSize(24.5.sp).<<.marginBottom(25.dip).>>

  STextView("ID")

  val userId = SEditText()

  STextView("Password")

  val pass = SEditText() inputType TEXT_PASSWORD

  SButton("Sign in", signin(userId.text, pass.text))

  new SLinearLayout {

    SButton("Help", openUri("http://help.url"))

    SButton("Sign up", openUri("http://signup.uri"))

  }.wrap.here

}.padding(20.dip)

```



Because a Scaloid layout description is plain Scala code, it is type-safe.



### Automatic layout converter



This converter turns an Android XML layout into a Scaloid layout:



http://layout.scaloid.org



### Migration tip 



Scaloid is fully compatible with legacy xml layout files. 

You can access a widget described in xml layout as:



```scala

onCreate {

  setContentView(R.layout.main)

  val name = find[EditText](R.id.name)

  // do something with `name`

}

```



### Responsive layout



Basically, a layout written in Scaloid is just an ordinary Scala code, so you can just freely composite the layout according to the device configuration:



```scala

import org.scaloid.util.Configuration._



if(long) SButton("This button is shown only for a long screen "

  + "dimension ("+ width + ", " + height + ")")

if(landscape) new SLinearLayout {

  SButton("Buttons for")

  SButton("landscape layout")

  if(dpi <= HDPI) SButton("You have a high resolution display!")

}.here

```



Please refer to this blog post for more detail:

 - [Syntactic sugar for multiple device configuration](http://blog.scaloid.org/2013/08/syntactic-sugar-for-multiple-device.html)



### Further readings about Scaloid layout 



 - [Accessing widgets in view class](http://blog.scaloid.org/2013/04/accessing-widgets-in-view-classes.html)

 - [Layout context](#layout-context)

 - [In-depth tutorial on styles](http://blog.scaloid.org/2013/01/a-css-like-styling-on-android.html)

 - [Styles for programmers](#styles-for-programmers)



## Lifecycle management



With Android API, Registering and unregistering BroadcastReceiver can be done as:



```scala

var connectivityListener: BroadcastReceiver = null



def onResume() {

  super.onResume()

  // ...

  connectivityListener = new BroadcastReceiver {

    def onReceive(context: Context, intent: Intent) {

     doSomething()

    }

  } 

  registerReceiver(connectivityListener, new IntentFilter(ConnectivityManager.CONNECTIVITY_ACTION))

}



def onPause() {

  unregisterReceiver(connectivityListener)

  // ...

  super.onPause()

}

```



In Scaloid, the directly equivalent code is:



```scala

broadcastReceiver(ConnectivityManager.CONNECTIVITY_ACTION) {

  doSomething()

}

```



Scaloid has highly flexible resource register/unregister management architecture.

If this code is written in services, registering and unregistering is done in onCreate and onDestroy respectively. 

If the same code is in activities, registering and unregistering is done in onResume and onPause respectively.

This is just a default behavior. 

You can override a preference that determine when the register/unregister preforms. 

Overriding it is simple as well:



```scala

broadcastReceiver(ConnectivityManager.CONNECTIVITY_ACTION) {

  doSomething()

}(this, onStartStop)

```



Then, the receiver is registered onStart, and unregistered onStop.



#### onDestroy can be called in many times!



You can declare `onDestroy` behaviors in many places. This simplifies resource management significantly. Suppose you want to open a stream from a file: 



```scala

def openFileStream(file: File): InputStream = {

  val stream = new FileInputStream(file)

  onDestroy(stream.close()) // automatically closed when the Activity is destroyed!!

  stream

}

```



`onDestroy` is a method that adds a function into the job list triggered when the activity is destroyed. So, we just get a stream from `openFileStream()` and forget about releasing it.

Other lifecycle states (`onCreate`, `onResume`, `onStop` and so on) can be treated in the same way.



**Further reading:** Refer to [this blog post](http://blog.scaloid.org/2013/02/better-resource-releasing-in-android.html) for more details.

 

 

## Asynchronous task processing



Android API provides `runOnUiThread()` only for class `Activity`. Scaloid provides a Scala version of `runOnUiThread()` for anywhere other than `Activity`.



Instead of:



```scala

activity.runOnUiThread {

  new Runnable() {

    def run() {

      debug("Running only in Activity class")

    }

  }

}

```



In Scaloid, use it like this:



```scala

runOnUiThread(debug("Running in any context"))

```



Running a job asynchronously and notifying the UI thread is a very frequently used pattern. Although Android API provides a helper class `AsyncTask`, implementing such a simple idea is still painful, even when we use Scala:



```scala

new AsyncTask[String, Void, String] {

  def doInBackground(params: Array[String]) = {

    doAJobTakeSomeTime(params)

  }



  override def onPostExecute(result: String) {

    alert("Done!", result)

  }

}.execute("param")

```



Using [`scala.concurrent.Future`](http://docs.scala-lang.org/sips/completed/futures-promises.html), the asynchronous job shown above can be rewritten like this:



```scala

Future {

  val result = doAJobTakeSomeTime(params)

  runOnUiThread(alert("Done!", result))

}

```



When you don't want to build sophisticate UI interactions, but just want to display something by calling a single Scaloid method (e.g. `alert`, `toast`, and `spinnerDialog`), Scaloid handles `runOnUiThread` for you. Therefore, the code block shown above is reduced to:



```scala

Future {

  alert("Done!", doAJobTakeSomeTime(params))

}

```



It is a great win as it exposes your idea clearly.



Just like we thrown away `AsyncTask`, we can also eliminate all other Java helpers for asynchronous job, such as `AsyncQueryHandler` and `AsyncTaskLoader`. Compare with the [original Java code](http://grepcode.com/file/repository.grepcode.com/java/ext/com.google.android/android-apps/4.1.1_r1/com/example/android/apis/view/ExpandableList2.java?av=h)

and a [Scala port](https://github.com/pocorall/scaloid-apidemos/blob/master/src/main/java/com/example/android/apis/view/ExpandableList2.scala) of ApiDemos example app.



Using `Future` is just an example of asynchronous task processing in Scaloid. You can freely use any modern task management utilities.



**Further reading:** Refer to [this blog post](http://blog.scaloid.org/2013/11/using-scalaconcurrentfuture-in-android.html) for an important consideration when using `Future` in Android.



## Implicit conversions

Scaloid employs several implicit conversions. Some of the available implicit conversions are shown below:



##### Uri conversion



```scala

String => Uri

```



The functions such as [play ringtones](#play-ringtones) `play()` or [open URIs](#open-uris) `openUri()` takes an instance of `Uri` as a parameter. However, we frequently have URIs as a `String`. Scaloid implicitly converts `String` into `Uri`. Therefore, you can freely use `String` when you play a ringtone:



```scala

play("content://media/internal/audio/media/50")

```



, open a URI:



```scala

openUri("http://scaloid.org")

```



, or wherever you want.



Alternatively, you can specify the conversion as:



```scala

val uri:Uri = "http://scaloid.org".toUri

```



##### Unit conversion



Units `dip` and `sp` can be converted into the pixel unit.



```scala

val inPixel:Int = 32.dip

val inPixel2:Int = 22.sp

```



Reversely, pixel unit can also be converted into `dip` and `sp` unit.



```scala

val inDip:Double = 35.px2dip

val inSp:Double = 27.px2sp

```



##### Resource IDs



Scaloid provides several implicit conversions that convert from `Int` type resource ID to `CharSequence`, `Array[CharSequence]`, `Array[String]`, `Drawable` and `Movie`.

For example:



```scala

def toast(msg:CharSequence) = ...



toast(R.string.my_message) // implicit conversion works!

```



Although Scaloid provides these conversions implicitly, explicit conversion may be required in some context. In this case, methods `r2...` are provided for the `Int` type:



```scala

warn("Will display the content of the resource: " + R.string.my_message.r2String)

```



Currently, `r2Text`, `r2TextArray`, `r2String`, `r2StringArray`, `r2Drawable` and `r2Movie` is provided.



**Further reading:**

 * [Why implicit conversion of Resource ID is cool?](https://github.com/pocorall/scaloid/wiki/Basics#wiki-why-implicit-conversion-of-resource-id-is-cool)



## Context as an implicit parameter

Many methods in the Android API require an instance of a class `Context`. Providing this for every method call results in clumsy code. We employ an implicit parameter to eliminate this. Just declare an implicit value that represents current context:



```scala

implicit val ctx = ...

```



or just extend trait `SContext`, which defines it for you. Then the code that required `Context` becomes much simpler, for example:



##### Intent



```scala

new Intent(context, classOf[MyActivity])

```



is reduced to:



```scala

SIntent[MyActivity]

```



When a method takes an `Intent` as a first parameter in which we want to pass the newly created intent object, the parameter can be omitted. For example:



```scala

startService(new Intent(context, classOf[MyService]))

stopService(new Intent(context, classOf[MyService]))

```



is reduced to:



```scala

startService[MyService]

stopService[MyService]

```



or



```scala

val intent = // initialize the intent and put some attributes on it

intent.start[MyActivity]

```



An intent that has a long list of extra attributes:



```scala

new Intent().putExtra("valueA", valueA).putExtra("valueB", valueB).putExtra("valueC", valueC)

```



is reduced to:



```scala

new Intent().put(valueA, valueB, valueC)

```



##### Toast



```scala

toast("hi, there!")

```



If you want a longer toast:



```scala

longToast("long toast")

```



##### Dialog



```scala

ProgressDialog.show(context, "Dialog", "working...", true)

```



is reduced to:



```scala

spinnerDialog("Dialog", "working...")

```



When you call `toast`, `longToast` or `spinnerDialog` from non-UI thread, you [don't have to mind about threading](#asynchronous-task-processing).

The toast example shown above is equivalent to the following Java code: 



```java

activity.runOnUiThread(new Runnable() {

    public void run() {

        Toast.makeText(activity, "hi, there!", Toast.LENGTH_SHORT).show();

    }

});

```



##### Pending intent



```scala

PendingIntent.getActivity(context, 0, new Intent(context, classOf[MyActivity]), 0)

PendingIntent.getService(context, 0, new Intent(context, classOf[MyService]), 0)

```



is reduced to:



```scala

pendingActivity[MyActivity]

pendingService[MyService]

```



##### Open URIs



This opens a web browser (or another view assigned to the http protocol).



```scala

openUri("http://scaloid.org")

```



##### System services



Getting system service objects become much simpler. The following legacy code:



```scala

val vibrator = context.getSystemService(Context.VIBRATOR_SERVICE).asInstanceOf[Vibrator]

vibrator.vibrate(500)

```



is reduced to:



```scala

vibrator.vibrate(500)

```



Under the hood, Scaloid defines a function `vibrator` like this:



```scala

def vibrator(implicit ctx: Context) = ctx.getSystemService(Context.VIBRATOR_SERVICE).asInstanceOf[Vibrator]

```



All the system service accessors available in Android API level 8 are defined (e.g. `audioManager`, `alarmManager`, `notificationManager`, etc.). The name of a system service accessor is the same as its class name, except that the first character is lowercased.



## Enriched Implicit classes



Suppose an Android class `Foo`, for example, Scaloid defines an implicit conversion `Foo => RichFoo`. The class `RichFoo` defines additional methods for more convenient access to `Foo`. This is a common pattern in Scala to extend existing API (see [pimp-my-library](http://www.artima.com/weblogs/viewpost.jsp?thread=179766) pattern). This section describes various features added on existing Android API classes.



##### Listeners



Android API defines many listener interfaces for callback notifications. For example, `View.OnClickListener` is used to be notified when a view is clicked:



```scala

find[Button](R.id.search).setOnClickListener(new View.OnClickListener {

  def onClick(v:View) {

    openUri("http://scaloid.org")

  }

})

```



Scaloid provides a shortcut that dramatically reduces the length of the code:



```scala

find[Button](R.id.search).onClick(openUri("http://scaloid.org"))

```



All other listener-appending methods such as `.onKey()`, `.onLongClick()`, and `.onTouch()` are defined.



Some conventions we employed for method naming are:



 * We omit `set...`, `add...`, and `...Listener` from the method name, which is less significant.


   For example, `.setOnKeyListener()` becomes `.onKey()`.

 * Every method has two versions of parameters overridden. One is a lazy parameter, and another is a function which has full parameters defined in the original Android API. For example, these two usages are valid:



```scala

button.onClick(info("touched"))

button.onClick((v:View) => info("touched a button "+v))

```



 * Methods `add...` is abbreviated with a method `+=` if it is not a listener-appender.


   For example, `layout.addView(button)` becomes `layout += button`.



##### Multiple method listeners



Methods `beforeTextChanged()`, `onTextChanged()`, and `afterTextChanged()` are defined in `RichTextView`, which can be implicitly converted from `TextView`. It is more convenient than using `TextWatcher` directly. For example:



```scala

inputField.beforeTextChanged(saveTextStatus())

```



is equivalent to:



```scala

inputField.addTextChangedListener(new TextWatcher {

  def beforeTextChanged(s: CharSequence, start: Int, before: Int, count: Int) {

    saveTextStatus()

  }



  def onTextChanged(p1: CharSequence, p2: Int, p3: Int, p4: Int) {}



  def afterTextChanged(p1: Editable) {}

})

```



Also, we override `beforeTextChanged()` with full parameters defined in the original listener:



```scala

inputField.beforeTextChanged((s:CharSequence, _:Int, _:Int) => saveText(s))

```



Other listeners in Android API can also be accessed in this way.



## Layout context



In Android API, layout information is stored into a `View` object via the method `View.setLayoutParams(ViewGroup.LayoutParams)`. A specific type of parameter passing into that method is determined by a the type of `...Layout` object which contains the `View` object. For example, let us see some Java code shown below:



```java

LinearLayout layout = new LinearLayout(context);

Button button = new Button(context);

button.setText("Click");

LinearLayout.LayoutParams params = new LinearLayout.LayoutParams();

params.weight = 1.0f;  // sets some value

button.setLayoutParams(params);

layout.addView(button);

```



Because the button is appended into the `LinearLayout`, the layout parameter must be `LinearLayout.LayoutParams`, otherwise a ___runtime error___ might be occurred. Meanwhile, Scaloid eliminate this burden, while still preserving rigorous typing of `LayoutParams`. The code shown below is equivalent to the previous Java code:



```scala

val layout = new SLinearLayout {

  SButton("Click").<<.Weight(1.0f).>>

}

```



In the anonymous constructor of 'SLinearLayout', Scaloid provides an implicit function called "layout context". This affects a return type of the method `<<` defined in the class `SButton`. 

If we use `SFrameLayout` as a layout context, the method `<<` returns `FrameLayout.LayoutParams`, which does not have `Weight` method. Therefore, the code below results a ___syntax error___.



```scala

val layout = new SFrameLayout {

  SButton("Click").<<.Weight(1.0f).>>   // Syntax error on Weight()

}

```



Compared with XML layout description, Scaloid layout is simple and type-safe.



The method `<<` is overloaded with parameters `<<(width:Int, height:Int)` which assigns the size of the view component. For example:



```scala

SButton("Click").<<(40.dip, WRAP_CONTENT)

```



#### Operator `new` and method `apply`



Usually, `View` components are referenced multiple times in an `Activity`. For example:



```scala

lazy val button = new SButton() text "Click"

onCreate {

  contentView = new SLinearLayout {

    button.here

  }

}

// ... uses the button somewhere in other methods (e.g. changing text or adding listeners)

```



[Prefixed classes](https://github.com/pocorall/scaloid/wiki/Basics#wiki-prefixed-classes) in Scaloid (e.g. `SButton`) have a companion object that implements `apply` methods that create a new component. These methods also append the component to the layout context that enclose the component. 

Therefore, the code block from the above example:



```scala

button = new SButton() text "Click"

button.here

```



is equivalent to:



```scala

button = SButton("Click")

```



Because the `apply` methods access to the layout context, it cannot be called outside of the layout context. 

In this case, use the `new` operator instead.



#### Method `>>`



As we noted, the method `<<` returns an object which is a type of `ViewGroup.LayoutParams`:



```scala

val params = SButton("Click").<<   // type LayoutParams

```



This class provides some setters for chaining:



```scala

val params = SButton("Click").<<.marginBottom(100).marginLeft(10)   // type LayoutParams

```



if we want use the `SButton` object again, Scaloid provides `>>` method returning back to the object:



```scala

val button = SButton("Click").<<.marginBottom(100).marginLeft(10).>>   // type SButton

```



#### Nested layout context



When the layout context is nested, inner-most layout's context is applied:



```scala

val layout = new SFrameLayout {

  new SLinearLayout {

    SButton("Click").<<.Weight(1.0f).>>   // in context of SLinearLayout

  }.here

}

```



#### Methods `fill`, `wrap`, `wf` and `fw`



When we get a `LayoutParams` from `<<`, the default values of `width` and `height` properties are `width = FILL_PARENT` and `height = WRAP_CONTENT`. You can override this when you need it:



```scala

SButton("Click").<<(FILL_PARENT, FILL_PARENT)

```



This is a very frequently used idiom. Therefore we provide further shorthand:



```scala

SButton("Click").<<.fill

```



If you want the `View` element to be wrapped,



```scala

SButton("Click").<<(WRAP_CONTENT, WRAP_CONTENT)

```



This is also shortened as:



```scala

SButton("Click").<<.wrap

```



Similarly, `<<(WRAP_CONTENT, FILL_PARENT)` and `<<(FILL_PARENT, WRAP_CONTENT)` can also be shortend as `<<.wf` and `<<.fw` respectively.



Because there are so many occurences `<<.wrap.>>` pattern in actual Android code, it is allowed to remove `.<<` and `.>>` in this case:



```scala

SButton("Click").wrap    // returns SButton type

```



This pattern also usable for `.fill`, `.fw` and `.wf` methods.



## Styles for programmers



#### Naming conventions



Scaloid follows the naming conventions of XML attributes in the Android API with some improvements.



For XML attributes, layout related properties are prefixed with `layout_` and as you might have guessed, Scaloid does not need it. 

For boolean attributes, the default is `false`. However, Scaloid flags it as `true` when the attribute is declared explicitly without any parameter. 

For example:



```scala

new SRelativeLayout {

  STextView("hello").<<.centerHorizontal.alignParentBottom.>>

}

```



Scaloid omits unnecessary `="true"` for the attribute `centerHorizontal`. Equivalent XML layout description for `TextView` is:



```xml



```



For layout methods named with four directions (e.g. `...Top`, `...Right`, `...Bottom` and `...Left`), Scaloid provides additional methods that specifies all properties at once. For example, Because Android XML layout defines `margin...` properties(`marginTop(v:Int)`, `marginRight(v:Int)`, `marginBottom(v:Int)` and `marginLeft(v:Int)`), Scaloid provides additional `margin(top:Int, right:Int, bottom:Int, left:Int)` and `margin(amount:Int)` methods that can be used as:



```scala

STextView("hello").<<.margin(5.dip, 10.dip, 5.dip, 10.dip)

```



or



```scala

STextView("hello").<<.margin(10.sp)  // assigns the same value for all directions

```



Android SDK introduced [styles](http://developer.android.com/guide/topics/ui/themes.html) to reuse common properties on XML layout.

We repeatedly pointed out that XML is verbose.

To apply styles in Scaloid, you do not need to learn any syntax or API library, because Scaloid layout is an ordinary Scala code. Just write a code that work as styles.



#### Basic: Assign it individually



Suppose the following code that repeats some properties:



```scala

SButton("first").textSize(20.dip).<<.margin(5.dip).>>

SButton("prev").textSize(20.dip).<<.margin(5.dip).>>

SButton("next").textSize(20.dip).<<.margin(5.dip).>>

SButton("last").textSize(20.dip).<<.margin(5.dip).>>

```



Then we can define a function that applies these properties:



```scala

def myStyle = (_: SButton).textSize(20.dip).<<.margin(5.dip).>>

myStyle(SButton("first"))

myStyle(SButton("prev"))

myStyle(SButton("next"))

myStyle(SButton("last"))

```



Still not satisfying? Here we have a shorter one:



```scala

def myStyle = (_: SButton).textSize(20.dip).<<.margin(5.dip).>>

List("first", "prev", "next", "last").foreach(title => myStyle(SButton(title)))

```



#### Advanced: CSS-like stylesheet



Scaloid provides `SViewGroup.style(View => View)` method to provide more generic component styling. 

The parameter is a function which receives a view requested for styling, and returns a view which is finished applying the style.

Then the example in the previous subsection becomes:



```scala

style {

  case b: SButton => b.textSize(20.dip).<<.margin(5.dip).>>

}



SButton("first")

SButton("prev")

SButton("next")

SButton("last")

```



Note that individually applying `myStyle` is reduced. Let us see another example:



```scala

style {

  case b: SButton => b.textColor(Color.RED).onClick(toast("Bang!"))

  case t: STextView => t.textSize(10.dip)

  case v => v.backgroundColor(Color.YELLOW)

}



STextView("I am 10.dip tall")

STextView("Me too")

STextView("I am taller than you").textSize(15.dip) // overriding

SEditText("Yellow input field")

SButton("Red alert!")

```

  

Similar to CSS, you can assign different styles for each classes using Scala pattern matching. 

Unlike Android XML styles or even CSS, Scaloid can assign some actions to the component (see `onclick(toast(...))`), or can do anything that you imagine. 

Also, you can easily override the property individually, as shown in the example above.



Last thing that you may missed: These are type-safe. If you made a mistake, compiler will check it for you.



**Further readings:**



 - [Accessing widgets in view class](http://blog.scaloid.org/2013/04/accessing-widgets-in-view-classes.html)

 - [In-depth tutorial on styles](http://blog.scaloid.org/2013/01/a-css-like-styling-on-android.html)

  

## Traits



### Trait `UnregisterReceiver`



When you register `BroadcastReceiver` with `Context.registerReceiver()` you have to unregister it to prevent memory leak. Trait `UnregisterReceiver` handles these chores for you. All you need to do is append the trait to your class.



```scala

class MyService extends SService with UnregisterReceiver {

  def func() {

    // ...

    registerReceiver(receiver, intentFilter)

    // Done! automatically unregistered at UnregisterReceiverService.onDestroy()

  }

}

```



### Trait `SActivity`



Instead of



```scala

findViewById(R.id.login).asInstanceOf[Button]

```



use a shorthand:



```scala

find[Button](R.id.login)

```



Although we provide this shorthand, Scaloid recommends [programmatically laying out UI, not with XML](https://github.com/pocorall/scaloid/wiki/UI-Layout-without-XML).



## Activity as an implicit parameter

Similar to the [implicit context](#context-as-an-implicit-parameter), an `Activity` typed implicit parameter is also required for some methods. Therefore, you have to define an activity as an implicit value:



```scala

implicit val ctx: Activity = ...

```



Because the class `Activity` is a subclass of `Context`, it can also be an implicit context.

When you extend `SActivity`, object `this` is assigned as the implicit activity by default.



Here we show some example cases of using the implicit activity:



#### Automatically allocate a unique `View` ID



Often, `Views` are required to have an ID value. Although Android API document specifies that the ID need not be unique, allocating unique ID is virtually mandatory in practice. Scaloid provides a package scope function `getUniqueId`, which returns `Int` type ID that is not allocated by any existing `View` components for given implicit activity.



```scala

val newUniqueIdForCurrentActivity = getUniqueId

```



Using this, Scaloid also extended `View` class to add a method `uniqueId`, that assigns a new unique ID if it is not already allocated. 



```scala

val uniqueIdOfMyView = myView.uniqueId

```



One of the good use case of `uniqueId` is `SRelativeLayout`. Some of the methods in this layout context, such as `below`, `above`, `leftOf` and `rightOf`, takes another `View` object as an anchor:



```scala

new SRelativeLayout {

  val btn = SButton(R.string.hi)

  SButton("There").<<.below(btn)

}

```



Here we show the implementation of the `below` function:



```scala

def below(anchor: View)(implicit activity: Activity) = {

  addRule(RelativeLayout.BELOW, anchor.uniqueId)

  this

}

```



A new unique ID is assigned to the `anchor` if it is not assigned already, and passes it to `addRule` function. 



## Logging



Unlike other logging frameworks, Android Logging API requires a `String` tag for every log call. We eliminate this by introducing an implicit parameter. Define an implicit value type of `LoggerTag` as shown:



```scala

implicit val loggerTag = LoggerTag("MyAppTag")

```



or, extend trait `TagUtil` or `SContext` which defines the tag by default. Then you can simply log like this:



```scala

warn("Something happened!")

```



Other functions for every log level (`verbose()`, `debug()`, `info()`, `warn()`, `error()` and `wtf()`) are available.



```scala

info("hello " + world)

```



A `String` parameter passed with `info()` is a by-name parameter, so it is evaluated only if the logging is possible. Therefore, the example shown above is equivalent to:



```scala

val tag = "MyAppTag"

if(Log.isLoggable(tag, Log.INFO)) Log.i(tag, "hello " + world)

```



## Scala getters and setters



You can use any of the setters listed below:



* `obj.setText("Hello")` Java bean style

* `obj.text = "Hello"` Assignment style

* `obj text "Hello"` DSL style

* `obj.text("Hello")` Method calling style



Compared to Java style getters and setters, for example:



```scala

new TextView(context) {

  setText("Hello")

  setTextSize(15)

}

```



that of Scala style clearly reveals the nature of the operations as shown below:



```scala

new STextView {

  text = "Hello"

  textSize = 15

}

```



Or, you can also chain the setters:



```scala

new STextView text "Hello" textSize 15

```



which is a syntactic sugar for:



```scala

new STextView.text("Hello").textSize(15)

```



We recommend "assignment style" and "DSL style". Use assignment style when you emphasize that you are assigning something, or use DSL style when the code length of the assignee is short and needs to be chained.



Note: Using `.apply(String)` method on object `STextView`, you can further reduce the code above like this:



```scala

STextView("Hello") textSize 15

```



**Further readings:**



 * [Return value of setters](https://github.com/pocorall/scaloid/wiki/Basics#wiki-return-value-of-setters)

 * [Prefixed classes](https://github.com/pocorall/scaloid/wiki/Basics#wiki-prefixed-classes)

 * [Sweet-little sugar](https://github.com/pocorall/scaloid/wiki/Basics#wiki-sweet-little-sugar)



## Classes



### Class `AlertDialogBuilder`



A Scala-style builder for AlertDialog.

 

```scala

new AlertDialogBuilder(R.string.title, R.string.message) {

  neutralButton()

}.show()

```



This displays an alert dialog with given string resources. We provide an equivalent shortcut:



```scala

alert(R.string.title, R.string.message)

```



Also you can build a more complex dialog:



```scala

new AlertDialogBuilder("Exit the app", "Do you really want to exit?") {

  positiveButton("Exit", finishTheApplication())

  negativeButton(android.R.string.cancel)

}.show()

```



The code above is equivalent to:



```scala

new AlertDialog.Builder(context)

  .setTitle("Exit the app")

  .setMessage("Do you really want to exit?")

  .setPositiveButton("Exit", new DialogInterface.OnClickListener {

    def onClick(dialog: DialogInterface, which: Int) {

      finishTheApplication()

    }

  })

  .setNegativeButton(android.R.string.cancel, new DialogInterface.OnClickListener {

    def onClick(dialog: DialogInterface, which: Int) {

      dialog.cancel()

    }

  }).show()

```



When you call `show()` or `alert` from non-UI thread, you [don't have to mind about threading](https://github.com/pocorall/scaloid/wiki/Basics#wiki-asynchronous-task-processing).



### Class `SArrayAdapter`



Suppose you want to let the user selects a string from spinner, and larger font should be displayed in the dropdown list.

Then the plain-old Android code is consisted of a chunk of XML and its wiring:



```XML



```

```scala

val adapter = new ArrayAdapter(context, android.R.layout.simple_spinner_item, Array("One", "Two", "Three"))

adapter.setDropDownViewResource(R.layout.spinner_dropdown)

```



In Scaloid, a directly equivalent code is:



```scala

SArrayAdapter("One", "Two", "Three").dropDownStyle(_.textSize(25.dip))

```



If you want to let the text color in the spinner be blue, use the `style` method:



```scala

SArrayAdapter("Quick", "Brown", "Fox").style(_.textColor(Color.BLUE))

```



Can it be simpler?



### Class `LocalService`



[Android Developer Guide on service binding](http://developer.android.com/guide/components/bound-services.html) says that we have to write more than 60 lines of code to define and bind an in-process service. 

With Scaloid, you can concisely define and access local service as shown below:



```scala

class MyService extends LocalService {

  private val generator = new Random()



  def getRandomNumber() = generator.nextInt(100)

}



class Activity extends SActivity {

  val random = new LocalServiceConnection[MyService]

 

  def onButtonClick(v:View) {

    random( s => toast("number: " + s.getRandomNumber()))

  }

}

```



**Further reading:** Refer to [this blog post](http://blog.scaloid.org/2013/03/introducing-localservice.html) to see why this is awesome in compared with the existing method.



### Class `Preferences`



SharedPreference can be accessed in this way:



```scala

val executionCount = preferenceVar(0) // default value 0

val ec = executionCount() // read

executionCount() = ec + 1 // write

executionCount.remove() // remove

```



**Further reading:**

 - [Type-safe SharedPreference](http://blog.scaloid.org/2015/07/type-safe-sharedpreference.html)

 - [A simple example: Prompt user to rate your app](http://blog.scaloid.org/2013/03/prompt-user-to-rate-your-android-app.html)



## Extending View class

Often we need to define a custom view widget for a specific requirement.

To do this, we define a class that inherits `android.widget.View` class or its subclass (e.g. `TextView` and `Button`).

To enable Scaloid extensions for this custom widget, you can define a class as follows:



```scala

class MyView(implicit ctx: Context) extends View(ctx) with TraitView[MyView] {

  def basis = this

  

  // custom code for MyView here

}

```



## Let's make it together!



Scaloid is an Apache licensed project. 

If you have any idea to improve Scaloid, feel free to open issues or post patches.

If you want look into inside of Scaloid, this document would be helpful:



 * [Inside Scaloid](https://github.com/pocorall/scaloid/wiki/Inside-Scaloid)



 

### [List of projects using Scaloid](https://github.com/pocorall/scaloid/wiki/Appendix#wiki-list-of-projects-using-scaloid)



### We are hiring!

The company behind Scaloid, onsquare is hiring Scala developers.

We are building [a music app](https://play.google.com/store/apps/details?id=com.soundcorset.client.android) and other amazing products.

We extensively uses Scaloid in our product, and probably it is the best reference of Scaloid application.

For more information about our company, please refer to our website http://o-n2.com .

Please send us your CV via email if you are interested in working at onsqure.

We are located at Incheon, Korea.

[email protected]