AsyncLayoutInflater.java
/*
* Copyright 2018 The Android Open Source Project
*
* 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.
*/
package androidx.asynclayoutinflater.view;
import android.content.Context;
import android.os.Handler;
import android.os.Handler.Callback;
import android.os.Looper;
import android.os.Message;
import android.util.AttributeSet;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import androidx.annotation.LayoutRes;
import androidx.annotation.NonNull;
import androidx.annotation.Nullable;
import androidx.annotation.UiThread;
import androidx.core.util.Pools.SynchronizedPool;
import java.util.concurrent.ArrayBlockingQueue;
/**
* <p>Helper class for inflating layouts asynchronously. To use, construct
* an instance of {@link AsyncLayoutInflater} on the UI thread and call
* {@link #inflate(int, ViewGroup, OnInflateFinishedListener)}. The
* {@link OnInflateFinishedListener} will be invoked on the UI thread
* when the inflate request has completed.
*
* <p>This is intended for parts of the UI that are created lazily or in
* response to user interactions. This allows the UI thread to continue
* to be responsive & animate while the relatively heavy inflate
* is being performed.
*
* <p>For a layout to be inflated asynchronously it needs to have a parent
* whose {@link ViewGroup#generateLayoutParams(AttributeSet)} is thread-safe
* and all the Views being constructed as part of inflation must not create
* any {@link Handler}s or otherwise call {@link Looper#myLooper()}. If the
* layout that is trying to be inflated cannot be constructed
* asynchronously for whatever reason, {@link AsyncLayoutInflater} will
* automatically fall back to inflating on the UI thread.
*
* <p>NOTE that the inflated View hierarchy is NOT added to the parent. It is
* equivalent to calling {@link LayoutInflater#inflate(int, ViewGroup, boolean)}
* with attachToRoot set to false. Callers will likely want to call
* {@link ViewGroup#addView(View)} in the {@link OnInflateFinishedListener}
* callback at a minimum.
*
* <p>This inflater does not support setting a {@link LayoutInflater.Factory}
* nor {@link LayoutInflater.Factory2}. Similarly it does not support inflating
* layouts that contain fragments.
*/
public final class AsyncLayoutInflater {
private static final String TAG = "AsyncLayoutInflater";
LayoutInflater mInflater;
Handler mHandler;
InflateThread mInflateThread;
public AsyncLayoutInflater(@NonNull Context context) {
mInflater = new BasicInflater(context);
mHandler = new Handler(mHandlerCallback);
mInflateThread = InflateThread.getInstance();
}
@UiThread
public void inflate(@LayoutRes int resid, @Nullable ViewGroup parent,
@NonNull OnInflateFinishedListener callback) {
if (callback == null) {
throw new NullPointerException("callback argument may not be null!");
}
InflateRequest request = mInflateThread.obtainRequest();
request.inflater = this;
request.resid = resid;
request.parent = parent;
request.callback = callback;
mInflateThread.enqueue(request);
}
private Callback mHandlerCallback = new Callback() {
@Override
public boolean handleMessage(Message msg) {
InflateRequest request = (InflateRequest) msg.obj;
if (request.view == null) {
request.view = mInflater.inflate(
request.resid, request.parent, false);
}
request.callback.onInflateFinished(
request.view, request.resid, request.parent);
mInflateThread.releaseRequest(request);
return true;
}
};
public interface OnInflateFinishedListener {
void onInflateFinished(@NonNull View view, @LayoutRes int resid,
@Nullable ViewGroup parent);
}
private static class InflateRequest {
AsyncLayoutInflater inflater;
ViewGroup parent;
int resid;
View view;
OnInflateFinishedListener callback;
InflateRequest() {
}
}
private static class BasicInflater extends LayoutInflater {
private static final String[] sClassPrefixList = {
"android.widget.",
"android.webkit.",
"android.app."
};
BasicInflater(Context context) {
super(context);
}
@Override
public LayoutInflater cloneInContext(Context newContext) {
return new BasicInflater(newContext);
}
@Override
protected View onCreateView(String name, AttributeSet attrs) throws ClassNotFoundException {
for (String prefix : sClassPrefixList) {
try {
View view = createView(name, prefix, attrs);
if (view != null) {
return view;
}
} catch (ClassNotFoundException e) {
// In this case we want to let the base class take a crack
// at it.
}
}
return super.onCreateView(name, attrs);
}
}
private static class InflateThread extends Thread {
private static final InflateThread sInstance;
static {
sInstance = new InflateThread();
sInstance.start();
}
public static InflateThread getInstance() {
return sInstance;
}
private ArrayBlockingQueue<InflateRequest> mQueue = new ArrayBlockingQueue<>(10);
private SynchronizedPool<InflateRequest> mRequestPool = new SynchronizedPool<>(10);
// Extracted to its own method to ensure locals have a constrained liveness
// scope by the GC. This is needed to avoid keeping previous request references
// alive for an indeterminate amount of time, see b/33158143 for details
public void runInner() {
InflateRequest request;
try {
request = mQueue.take();
} catch (InterruptedException ex) {
// Odd, just continue
Log.w(TAG, ex);
return;
}
try {
request.view = request.inflater.mInflater.inflate(
request.resid, request.parent, false);
} catch (RuntimeException ex) {
// Probably a Looper failure, retry on the UI thread
Log.w(TAG, "Failed to inflate resource in the background! Retrying on the UI"
+ " thread", ex);
}
Message.obtain(request.inflater.mHandler, 0, request)
.sendToTarget();
}
@Override
public void run() {
while (true) {
runInner();
}
}
public InflateRequest obtainRequest() {
InflateRequest obj = mRequestPool.acquire();
if (obj == null) {
obj = new InflateRequest();
}
return obj;
}
public void releaseRequest(InflateRequest obj) {
obj.callback = null;
obj.inflater = null;
obj.parent = null;
obj.resid = 0;
obj.view = null;
mRequestPool.release(obj);
}
public void enqueue(InflateRequest request) {
try {
mQueue.put(request);
} catch (InterruptedException e) {
throw new RuntimeException(
"Failed to enqueue async inflate request", e);
}
}
}
}