https://github.com/sockeqwe/adapterdelegates
"Favor composition over inheritance" for RecyclerView Adapters
https://github.com/sockeqwe/adapterdelegates
adapterdelegates composition-over-inheritance delegate recyclerview recyclerview-adapter
Last synced: 10 months ago
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"Favor composition over inheritance" for RecyclerView Adapters
- Host: GitHub
- URL: https://github.com/sockeqwe/adapterdelegates
- Owner: sockeqwe
- License: apache-2.0
- Created: 2015-07-29T11:19:56.000Z (over 10 years ago)
- Default Branch: master
- Last Pushed: 2024-04-18T09:55:42.000Z (almost 2 years ago)
- Last Synced: 2025-04-04T11:38:53.338Z (11 months ago)
- Topics: adapterdelegates, composition-over-inheritance, delegate, recyclerview, recyclerview-adapter
- Language: Java
- Homepage: http://hannesdorfmann.com/android/adapter-delegates
- Size: 978 KB
- Stars: 2,938
- Watchers: 74
- Forks: 315
- Open Issues: 17
-
Metadata Files:
- Readme: README.md
- License: LICENSE
Awesome Lists containing this project
README
# AdapterDelegates
Read the motivation for this project in [my blog post](http://hannesdorfmann.com/android/adapter-delegates).
The idea of this library is to build your adapters by composing reusable components.
Favor composition over inheritance
The idea is that you define an AdapterDelegate for each view type.
This delegate is responsible for creating ViewHolder and binding ViewHolder for a certain viewtype.
Then you can compose your RecyclerView Adapter by registering the AdapterDelegates that you really need.
### Changelog
See [releases section](https://github.com/sockeqwe/AdapterDelegates/releases)
# Quickstart: Kotlin DSL
There are 2 artifacts for kotlin users that allow you to write Adapter Delegates more convenient by providing a `DSL`:
## Dependencies
```
implementation 'com.hannesdorfmann:adapterdelegates4-kotlin-dsl:4.3.2'
// If you use Kotlin Android Extensions and synthetic properties (alternative to findViewById())
implementation 'com.hannesdorfmann:adapterdelegates4-kotlin-dsl-layoutcontainer:4.3.2'
// If you use ViewBinding
implementation 'com.hannesdorfmann:adapterdelegates4-kotlin-dsl-viewbinding:4.3.2'
```
## How to use it
```kotlin
fun catAdapterDelegate(itemClickedListener : (Cat) -> Unit) = adapterDelegate(R.layout.item_cat) {
// This is the initializer block where you initialize the ViewHolder.
// Its called one time only in onCreateViewHolder.
// this is where you can call findViewById() and setup click listeners etc.
val name : TextView = findViewById(R.id.name)
name.setClickListener { itemClickedListener(item) } // Item is automatically set for you. It's set lazily though (set in onBindViewHolder()). So only use it for deferred calls like clickListeners.
bind { diffPayloads -> // diffPayloads is a List containing the Payload from your DiffUtils
// This is called anytime onBindViewHolder() is called
name.text = item.name // Item is of type Cat and is the current bound item.
}
}
```
In case you want to use kotlin android extensions and synthetic properties (as alternative to findViewById()) use `adapterDelegateLayoutContainer` instead of `adapterDelegate` like this:
```kotlin
fun catAdapterDelegate(itemClickedListener : (Cat) -> Unit) = adapterDelegateLayoutContainer(R.layout.item_cat) {
name.setClickListener { itemClickedListener(item) } // no need for findViewById(). Name is imported as synthetic property from kotlinx.android.synthetic.main.item_cat
bind { diffPayloads ->
name.text = item.name
}
}
```
If you use `adapterDelegateLayoutContainer()` don't forget to add
```
androidExtensions {
experimental = true
}
```
to your build.gradle to enable LayoutContainer.
In case you want to use ViewBinding\DataBinding use `adapterDelegateViewBinding` instead of `adapterDelegate` like this:
```kotlin
fun cat2AdapterDelegate(itemClickedListener : (Cat) -> Unit) = adapterDelegateViewBinding(
{ layoutInflater, root -> ItemCatBinding.inflate(layoutInflater, root, false) }
) {
binding.name.setOnClickListener {
itemClickedListener(item)
}
bind {
binding.name.text = item.name
}
}
```
You have to specify if a specific AdapterDelegate is responsible for a specific item.
Per default this is done with an `instanceof` check like `item instanceof Cat`.
You can override this if you want to handle it in a custom way by setting the `on` lambda
and return true or false:
```kotlin
adapterDelegate (
layout = R.layout.item_cat,
on = { item: Animal, items: List, position: Int ->
if (item is Cat && position == 0)
true // return true: this adapterDelegate handles it
else
false // return false
}
){
...
bind { ... }
}
```
The same `on` parameter is available for `adapterDelegateLayoutContainer()` and `adapterDelegateViewBinding()` DSL.
### Compose your Adapter
Finally, you can compose your `RecyclerView Adapter` by registering your AdapterDelegates like this:
```kotlin
val adapter = ListDelegationAdapter>(
catAdapterDelegate(...),
dogAdapterDelegate(),
snakeAdapterDelegate()
)
```
### `fun` vs. `val`
You could define your AdapterDelegate also as TopLevel `val` like this:
```kotlin
// top level property inside CatDelegate.kt
val catDelegate = adapterDelegate {
...
bind { ... }
}
```
but a top level val is a static field at the end so that this adapter delegate will be kept for the
lifetime of your application in memory.
Therefore, we would recommend to prefer write your AdapterDelegate as a function and call this function to
actually instantiate the AdapterDelegate.
Then the AdapterDelegate can be garbage collected as soon as the user leaves the screen the
AdapterDelegate is used in.
```kotlin
// top level function inside CatDelegate.kt
fun catAdapterDelegate() = adapterDelegate {
...
bind { ... }
}
```
## Dependencies if you don't use Kotlin DSL
This library is available on maven central:
```groovy
implementation 'com.hannesdorfmann:adapterdelegates4:4.3.2'
```
[](https://travis-ci.org/sockeqwe/AdapterDelegates)
Please note that since 4.0 the group id has been changed to `adapterdelegates4`.
### Snapshot
```groovy
implementation 'com.hannesdorfmann:adapterdelegates4:4.3.3-SNAPSHOT'
```
You also have to add the url to the snapshot repository:
```groovy
allprojects {
repositories {
...
maven { url "https://oss.sonatype.org/content/repositories/snapshots/" }
}
```
## How to use it in Java
The idea of this library is to build your adapters by composing reusable components.
> Favor composition over inheritance
The idea is that you define an `AdapterDelegate` for each view type. This delegate is responsible for creating ViewHolder and binding ViewHolder for a certain viewtype.
An `AdapterDelegate` get added to an `AdapterDelegatesManager`. This manager is the man in the middle between `RecyclerView.Adapter` and each `AdapterDelegate`.
For example:
```java
public class CatAdapterDelegate extends AdapterDelegate> {
private LayoutInflater inflater;
public CatAdapterDelegate(Activity activity) {
inflater = activity.getLayoutInflater();
}
@Override public boolean isForViewType(@NonNull List items, int position) {
return items.get(position) instanceof Cat;
}
@NonNull @Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent) {
return new CatViewHolder(inflater.inflate(R.layout.item_cat, parent, false));
}
@Override public void onBindViewHolder(@NonNull List items, int position,
@NonNull RecyclerView.ViewHolder holder, @Nullable List payloads) {
CatViewHolder vh = (CatViewHolder) holder;
Cat cat = (Cat) items.get(position);
vh.name.setText(cat.getName());
}
static class CatViewHolder extends RecyclerView.ViewHolder {
public TextView name;
public CatViewHolder(View itemView) {
super(itemView);
name = (TextView) itemView.findViewById(R.id.name);
}
}
}
```
Please note that `onBindViewHolder()` last parameter `payloads` is null unless you use from `adapter.notify`. There are more methods like `onViewRecycled(ViewHolder)`, `onFailedToRecycleView(ViewHolder)`,
`onViewAttachedToWindow(ViewHolder)` and `onViewDetachedFromWindow(ViewHolder)` you can override in your `AdapterDelegate` class.
Then an `AnimalAdapter` could look like this:
```java
public class AnimalAdapter extends RecyclerView.Adapter {
private AdapterDelegatesManager> delegatesManager;
private List items;
public AnimalAdapter(Activity activity, List items) {
this.items = items;
delegatesManager = new AdapterDelegatesManager<>();
// AdapterDelegatesManager internally assigns view types integers
delegatesManager.addDelegate(new CatAdapterDelegate(activity))
.addDelegate(new DogAdapterDelegate(activity))
.addDelegate(new GeckoAdapterDelegate(activity));
// You can explicitly assign integer view type if you want to
delegatesManager.addDelegate(23, new SnakeAdapterDelegate(activity));
}
@Override public int getItemViewType(int position) {
return delegatesManager.getItemViewType(items, position);
}
@Override public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
return delegatesManager.onCreateViewHolder(parent, viewType);
}
@Override public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
delegatesManager.onBindViewHolder(items, position, holder);
}
@Override public int getItemCount() {
return items.size();
}
}
```
## Reducing boilerplate code
As you have seen in the code snippet above this may require to write the same boiler plate code again and again to hook in `AdapterDelegatesManager` to `Adapter`.
This can be reduced by extending either from `ListDelegationAdapter` if the data source the adapter displays is `java.util.List>` or `AbsDelegationAdapter` which is a more general one (not limited to `java.util.List`)
#### ListDelegationAdapter
For example the same `AnimalAdapter` from above could be simplified as follows by extending from `ListDelegationAdapter`:
```java
public class AnimalAdapter extends ListDelegationAdapter> {
public AnimalAdapter(Activity activity, List items) {
// DelegatesManager is a protected Field in ListDelegationAdapter
delegatesManager.addDelegate(new CatAdapterDelegate(activity))
.addDelegate(new DogAdapterDelegate(activity))
.addDelegate(new GeckoAdapterDelegate(activity))
.addDelegate(23, new SnakeAdapterDelegate(activity));
// Set the items from super class.
setItems(items);
}
}
```
#### AbsListItemAdapterDelegate
Also you may have noticed that you often have to write boilerplate code to cast items and ViewHolders when working with list of items as adapters dataset source.
`AbsListItemAdapterDelegate` can help you here. Let's take this class to create a `CatListItemAdapterDelegate` similar to the `CatAdapterDelegate` from top of this page but without the code for casting items.
```java
public class CatListItemAdapterDelegate extends AbsListItemAdapterDelegate {
private LayoutInflater inflater;
public CatAdapterDelegate(Activity activity) {
inflater = activity.getLayoutInflater();
}
@Override public boolean isForViewType(Animal item, List items, int position) {
return item instanceof Cat;
}
@Override public CatViewHolder onCreateViewHolder(ViewGroup parent) {
return new CatViewHolder(inflater.inflate(R.layout.item_cat, parent, false));
}
@Override public void onBindViewHolder(Cat item, CatViewHolder vh, @Nullable List payloads) {
vh.name.setText(item.getName());
}
static class CatViewHolder extends RecyclerView.ViewHolder {
public TextView name;
public CatViewHolder(View itemView) {
super(itemView);
name = (TextView) itemView.findViewById(R.id.name);
}
}
}
```
As you see, instead of writing code that casts list item to Cat we can use `AbsListItemAdapterDelegate` to do the same job (by declaring generic types).
## DiffUtil & ListAdapter = AsyncListDifferDelegationAdapter
Support library 27.0.1 introduced `ListAdapter` - the new extension of `RecyclerView.Adapter` that uses `AsyncListDiffer` internally. It does calculating diff in the background thread by default and does all particular animations for you items collection. Hence you don't need carry about `notify*` methods, `AsyncListDiffer` does all the job for you. And AdapterDelegates supports it too.
This library offers the equivalent to `ListAdapter` which is called `AsyncListDifferDelegationAdapter` that can be used together with any regular `AdapterDelegate`.
```java
public class DiffAdapter extends AsyncListDifferDelegationAdapter {
public DiffAdapter() {
super(DIFF_CALLBACK) // Your diff callback for diff utils
delegatesManager
.addDelegate(new DogAdapterDelegate());
.addDelegate(new CatAdapterDelegate());
}
}
```
## Pagination
There is an additional artifact for the pagination library:
```gradle
implementation 'com.hannesdorfmann:adapterdelegates4-pagination:4.3.2'
```
Use `PagedListDelegationAdapter`.
## Fallback AdapterDelegate
What if your adapter's data source contains a certain element you don't have registered an `AdapterDelegate` for? In this case the `AdapterDelegateManager` will throw an exception at runtime. However, this is not always what you want. You can specify a fallback `AdapterDelegate` that will be used if no other `AdapterDelegate` has been found to handle a certain view type.
```java
AdapterDelegate fallbackDelegate = ...;
adapterDelegateManager.setFallbackDelegate( fallbackDelegate );
```
Note also that boolean return type of `isForViewType()` of a fallback delegate will be ignored (will not be take into account). So it doesn't matter if you return true or false. You can use `AbsFallbackAdapterDelegate` that already implements `isForViewType()` so that you only have to override `onCreateViewHolder()` and `onBindViewHolder()` for your fallback adapter delegate.
## Version 3.x to 4.0 migration
`AdapterDelegates3` uses `com.android.support:recyclerview-v7:x.y.z` whereas `AdapterDelegates4` uses
`androidx.recyclerview:recyclerview:1.0.0`.
Migration should be easy. Just use IntelliJ IDE or Android Studio 'Replace in Path' (can be found inside `Edit` main menu then `Find` submenu):
Replace `com.hannesdorfmann.adapterdelegates3` with `com.hannesdorfmann.adapterdelegates4`.
You might also have to replace `android.support.v7.widget.RecyclerView` with `androidx.recyclerview.widget.RecyclerView` and
`android.support.annotation.NonNull` with `androidx.annotation.NonNull`.
## License
```
Copyright 2015 Hannes Dorfmann
Licensed under the Apache License, Version 2.0 (the "License");
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an "AS IS" BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
```