Concatapter tutorial

1. Preface

2021 year 4 month 7 Japan Android The team officially released RecyclerView 1.2.0 edition . be relative to 1.1.0 edition , It has two major changes ：

1. Added ConcatAdapter： This Adapter Conveniently, let's work in a RecyclerView Connecting multiple Adapters.
2. Supports delayed recovery state ：RecyclerView Now it supports restoring the state when the content is loaded .

This article will combine ConcatAdapter Simple use , From simple to deep ConcatAdapter Advanced use of .

2. Easy to use

The implementation above is a list of text , Here's the effect of the button list , Pictured ：

2.1 Don't use ConcatAdapter Realization

stay RecyclerView 1.2.0 Before , We can go through Adapte Of getItemViewType Method , Set the text and button types . To achieve the above effect . The pseudocode is as follows , adopt TEXT_TYPE and BUTTON_TYPE Two types of , Create different views .

2.2 Use ConcatAdapter Realization

Use ConcatAdapter Achieve this effect . Just create TextAdapter Working with text lists , establish ButtonAdapter Handle the list of buttons . adopt ConcatAdapter Connect them in series . The code is as follows ：

2.3 Advantages and disadvantages

Use ConcatAdapter The advantage is Adapter High reusability , More focused on the business , There's no need to think about the differences ItemType Scene , Low coupling . The disadvantage is ,ConcatAdapter No support for different ItemType Scenes that cross over .

3. Advanced

That's all ConcatAdapter Simple use of all the tutorials . But if you think ConcatAdapter If it's that simple, you're totally wrong . Let's go deep into the source code , Play with more advanced features .

3.1 Config class

We see ConcatAdapter It has the following constructors . We noticed that Config Class is ConcatAdapter The static inner class of .

public ConcatAdapter(Adapter<? extends ViewHolder>... adapters) {
    this(Config.DEFAULT, adapters);
}

public ConcatAdapter(Config config, Adapter<? extends ViewHolder>... adapters) {
    this(config, Arrays.asList(adapters));
}

Config The constructor is as follows ：

Config(boolean isolateViewTypes, StableIdMode stableIdMode) {
    this.isolateViewTypes = isolateViewTypes;
    this.stableIdMode = stableIdMode;
}

public static final Config DEFAULT = new Config(true, NO_STABLE_IDS);

We notice that the default Config,isolateViewTypes The value is true.

3.2 isolateViewTypes meaning

Make it clear isolateViewTypes The meaning of , Then you have to understand viewType The relationship with cache . We all know RecyclerViewPool According to viewType cache ViewHolder Of . If viewType identical , So its corresponding cache pool is the same .

RecyclerViewPool The cache diagram is as follows . Each is different viewType Each has its own cache .

isolateViewTypes by true. Express ConcatAdapter The son of Adapter Of viewType, Will be ConcatAdapter To separate from each other . Even if two people Adapter Of the elements of viewType identical ,ConcatAdapter Will separate them into different viewType. From the perspective of caching , Even if two are the same Adapter, They also can't share a cache pool .

isolateViewTypes by false. Said if viewType identical , Then they will share a cache pool .

3.1 Cache not shared

Suppose there is ConcatAdapter, Connected to RedAdapter、OrangeAdapter、BlueAdapter、RedAdapter. Use the default Config.isolateViewTypes by true, We see RedAdapter Of ViewType Default return 1. But from ConcatAdapter The angle of . Two RedAdapter Of viewType Respectively 0 and 3.

RedAdapter redAdapter1 = xxx;
OrangeAdapter orangerAdapter = xxx;
BlueAdapter blueAdapter = xxx;
RedAdapter redAdapter2 = xxx;

ConcatAdapter concatenated = new ConcatAdapter(redAdapter1, orangerAdapter,blueAdapter,redAdapter2);
recyclerView.setAdapter(concatenated);

3.2 Shared cache

RedAdapter redAdapter1 = xxx;
OrangeAdapter orangerAdapter = xxx;
BlueAdapter blueAdapter = xxx;
RedAdapter redAdapter2 = xxx;

//isolateViewTypes by false
ConcatAdapter.Config config = ConcatAdapter.Config.Builder().setIsolateViewTypes(false).build()

ConcatAdapter concatenated = new ConcatAdapter(config, redAdapter1, orangerAdapter,blueAdapter,redAdapter2);
recyclerView.setAdapter(concatenated);

ConcatAdapter Of itemType Hezi Adapter Of itemType Agreement .

4. Climb a pit

4.1 A pit

Son Adapter Of getItemViewType Return default .ConcatAdapter isolateViewType Set to false.

TextAdapter and ButtonAdapter As above .

class ConcatAdapterDemoActivity : AppCompatActivity() {
    override fun onCreate(savedInstanceState: Bundle?) {
        super.onCreate(savedInstanceState)
        setContentView(R.layout.activity_concat_adapter_demo)
        val recyclerView = findViewById<RecyclerView>(R.id.recyclerview)
        recyclerView.layoutManager = LinearLayoutManager(this)
        val config = ConcatAdapter.Config.Builder().setIsolateViewTypes(false).build()
        recyclerView.adapter = ConcatAdapter(
            config,
            TextAdapter(),
            ButtonAdapter()
        )
    }
}

4.2 Pit two

ConcatAdapter Connect multiple TextAdapter.isolateViewType Set to true. Found scrolling to the second TextAdapter When in position , A new TextView. This situation , identical viewType Need to share cache . take isolateViewType Set to false.

recyclerView.adapter = ConcatAdapter(
      config,
      TextAdapter(),
      ButtonAdapter(),
      TextAdapter()
)

5. principle

1. ConcatAdapter.getItemViewType()

//ConcatAdapter.java
@Override
public int getItemViewType(int position) {
    return mController.getItemViewType(position);
}

2. ConcatAdapterController.getItemViewType(int globalPosition)

//ConcatAdapterController.java
public int getItemViewType(int globalPosition) {
      // according to globalPosition Find the corresponding sub Adapter Of Wrapper
      WrapperAndLocalPosition wrapperAndPos = findWrapperAndLocalPosition(globalPosition);
      int itemViewType = wrapperAndPos.mWrapper.getItemViewType(wrapperAndPos.mLocalPosition);
      releaseWrapperAndLocalPosition(wrapperAndPos);
      return itemViewType;
}

3. NestedAdapterWrapper.getItemViewType(int localPosition)

int getItemViewType(int localPosition) {
    return mViewTypeLookup.localToGlobal(adapter.getItemViewType(localPosition));
}

4. IsolatedViewTypeStorage$WrapperViewTypeLookup.localToGlobal()

@Override
public int localToGlobal(int localType) {
    int index = mLocalToGlobalMapping.indexOfKey(localType);
    if (index > -1) {
        return mLocalToGlobalMapping.valueAt(index);
    }
    // get a new key.
    int globalType = obtainViewType(mWrapper);
    mLocalToGlobalMapping.put(localType, globalType);
    mGlobalToLocalMapping.put(globalType, localType);
    return globalType;
}

5. IsolatedViewTypeStorage$WrapperViewTypeLookup. As you can see from the code, without sharing the cache pool . Son Adapter Of viewType From 0 Incremental correspondence

int mNextViewType = 0;
int obtainViewType(NestedAdapterWrapper wrapper) {
    int nextId = mNextViewType++;
    mGlobalTypeToWrapper.put(nextId, wrapper);
    return nextId;
}

6. isolateViewTypes by true Under the circumstances . Will use SharedIdRangeViewTypeStorage$WrapperViewTypeLookup. We see localType and globalType equal .

@Override
public int localToGlobal(int localType) {
    // register it first
    List<NestedAdapterWrapper> wrappers = mGlobalTypeToWrapper.get(
            localType);
    if (wrappers == null) {
        wrappers = new ArrayList<>();
        mGlobalTypeToWrapper.put(localType, wrappers);
    }
    if (!wrappers.contains(mWrapper)) {
        wrappers.add(mWrapper);
    }
    return localType;
}

@Override
public int globalToLocal(int globalType) {
    return globalType;
}

6. Last

The final writing was a little hasty . Some points were not explained clearly . If you have any questions, please leave a message . Welcome to WeChat official account. “ Byte station ”. Get more dry articles .