Android布局优化（三）使用AsyncLayoutInflater异步加载布局
16lz
2021-12-04
系列文章
- Android布局优化（一）LayoutInflate — 从布局加载原理说起
- Android布局优化（二）优雅获取界面布局耗时
- Android布局优化（三）使用AsyncLayoutInflater异步加载布局
- Android布局优化（四）X2C — 提升布局加载速度200%
- Android布局优化（五）绘制优化—避免过度绘制
目录
前言
在Android布局优化（一）从布局加载原理说起中我们说到了布局加载的两大性能瓶颈，通过IO操作将XML加载到内存中并进行解析和通过反射创建View。当xml文件过大或页面文件过深，布局的加载就会较为耗时。我们知道，当主线程进行一些耗时操作可能就会导致页面卡顿，更严重的可能会产生ANR，所以我们能如何来进行布局加载优化呢？解决这个问题有两种思路，直接解决和侧面缓解。直接解决就是不使用IO和反射等技术（这个我们会在下一节进行介绍）。侧面缓解的就是既然耗时操作难以避免，那我们能不能把耗时操作放在子线程中，等到inflate操作完成后再将结果回调到主线程呢？答案当然是可以的，Android为我们提供了AsyncLayoutInflater类来进行异步布局加载
AsyncLayoutInflater用法
AsyncLayoutInflater的使用非常简单，就是把setContentView和一些view的初始化操作都放到了onInflateFinished回调中
@Overrideprotected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); new AsyncLayoutInflater(this).inflate(R.layout.activity_main,null, new AsyncLayoutInflater.OnInflateFinishedListener(){ @Override public void onInflateFinished(View view, int resid, ViewGroup parent) { setContentView(view); rv = findViewById(R.id.tv_right); rv.setLayoutManager(new V7LinearLayoutManager(MainActivity.this)); rv.setAdapter(new RightRvAdapter(MainActivity.this)); } });}AsyncLayoutInflater源码分析
AsyncLayoutInflater的源码非常短，也比较容易理解，总共只有170行左右
AsyncLayoutInflater构造方法和初始化
构造方法中做了三件事件
创建
BasicInflater创建
Handler创建
InflateThread
inflate方法创建一个InflateRequest对象，并将resid、parent、callback等变量存储到这个对象中，并调用enqueue方法向队列中添加一个请求
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); } ....}InflateThread
这个类的主要作用就是创建一个子线程，将inflate请求添加到阻塞队列中，并按顺序执行BasicInflater.inflate操作（BasicInflater实际上就是LayoutInflater的子类）。不管infalte成功或失败后，都会将request消息发送给主线程做处理
private static class InflateThread extends Thread { private static final InflateThread sInstance; static { sInstance = new InflateThread(); sInstance.start(); } public static InflateThread getInstance() { return sInstance; } //生产者-消费者模型，阻塞队列 private ArrayBlockingQueue mQueue = new ArrayBlockingQueue<>(10); //使用了对象池来缓存InflateThread对象，减少对象重复多次创建，避免内存抖动 private SynchronizedPool mRequestPool = new SynchronizedPool<>(10); public void runInner() { InflateRequest request; try { //从队列中取出一条请求，如果没有则阻塞 request = mQueue.take(); } catch (InterruptedException ex) { // Odd, just continue Log.w(TAG, ex); return; } try { //inflate操作（通过调用BasicInflater类） request.view = request.inflater.mInflater.inflate( request.resid, request.parent, false); } catch (RuntimeException ex) { // 回退机制：如果inflate失败，回到主线程去inflate Log.w(TAG, "Failed to inflate resource in the background! Retrying on the UI" + " thread", ex); } //inflate成功或失败，都将request发送到主线程去处理 Message.obtain(request.inflater.mHandler, 0, request) .sendToTarget(); } @Override public void run() { //死循环（实际不会一直执行，内部是会阻塞等待的） while (true) { runInner(); } } //从对象池缓存中取出一个InflateThread对象 public InflateRequest obtainRequest() { InflateRequest obj = mRequestPool.acquire(); if (obj == null) { obj = new InflateRequest(); } return obj; } //对象池缓存中的对象的数据清空，便于对象复用 public void releaseRequest(InflateRequest obj) { obj.callback = null; obj.inflater = null; obj.parent = null; obj.resid = 0; obj.view = null; mRequestPool.release(obj); } //将inflate请求添加到ArrayBlockingQueue（阻塞队列）中 public void enqueue(InflateRequest request) { try { mQueue.put(request); } catch (InterruptedException e) { throw new RuntimeException( "Failed to enqueue async inflate request", e); } }} InflateRequest
InflateRequest其实就可以理解为主线程和子线程之间传递的数据模型，类似Message的作用
private static class InflateRequest { AsyncLayoutInflater inflater; ViewGroup parent; int resid; View view; OnInflateFinishedListener callback; InflateRequest() { }}BasicInflater
BasicInflater 继承自 LayoutInflater，只是覆写了 onCreateView：优先加载这三个前缀的 Layout，然后才按照默认的流程去加载，因为大多数情况下我们 Layout 中使用的View都在这三个 package 下
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 { //优先加载"android.widget.”、 "android.webkit."、"android.app." View view = createView(name, prefix, attrs); if (view != null) { return view; } } catch (ClassNotFoundException e) { } } return super.onCreateView(name, attrs); }}mHandlerCallback
这里就是在主线程中handleMessage的操作，这里有一个回退机制，就是当子线程中inflate失败后，会继续再主线程中进行inflate操作，最终通过OnInflateFinishedListener接口将view回调到主线程
private Callback mHandlerCallback = new Callback() { @Override public boolean handleMessage(Message msg) { InflateRequest request = (InflateRequest) msg.obj; if (request.view == null) { //view == null说明inflate失败 //继续再主线程中进行inflate操作 request.view = mInflater.inflate( request.resid, request.parent, false); } //回调到主线程 request.callback.onInflateFinished( request.view, request.resid, request.parent); mInflateThread.releaseRequest(request); return true; }};OnInflateFinishedListener
布局加载完成后，通过OnInflateFinishedListener将加载完成后的view回调出来
public interface OnInflateFinishedListener { void onInflateFinished(View view, int resid, ViewGroup parent);}AsyncLayoutInflater的局限性及改进
使用AsyncLayoutInflate主要有如下几个局限性：
所有构建的
View中必须不能直接使用Handler或者是调用Looper.myLooper()，因为异步线程默认没有调用Looper.prepare ()异步转换出来的 View 并没有被加到 parent view中，
AsyncLayoutInflater是调用了LayoutInflater.inflate(int, ViewGroup, false)，因此如果需要加到 parent view 中，就需要我们自己手动添加；AsyncLayoutInflater不支持设置LayoutInflater.Factory或者LayoutInflater.Factory2同时缓存队列默认 10 的大小限制如果超过了10个则会导致主线程的等待
使用单线程来做全部的
inflate工作，如果一个界面中layout很多不一定能满足需求
那我们如何来解决这些问题呢？AsyncLayoutInflate类修饰为 final ，所以不能通过继承重写父类来实现。庆幸的是AsyncLayoutInflate的代码非常短而且相对简单，所以我们可以直接把AsyncLayoutInflate的代码复制出来一份，然后在这基础之上进行改进优化
接下来我们主要从两个方面来进行优化
引入线程池，减少单线程等待
手动设置setFactory2
直接上代码
public class AsyncLayoutInflatePlus { private static final String TAG = "AsyncLayoutInflatePlus"; private Pools.SynchronizedPool mRequestPool = new Pools.SynchronizedPool<>(10); LayoutInflater mInflater; Handler mHandler; Dispather mDispatcher; public AsyncLayoutInflatePlus(@NonNull Context context) { mInflater = new BasicInflater(context); mHandler = new Handler(mHandlerCallback); mDispatcher = new Dispather(); } @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 = obtainRequest(); request.inflater = this; request.resid = resid; request.parent = parent; request.callback = callback; mDispatcher.enqueue(request); } private Handler.Callback mHandlerCallback = new Handler.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); releaseRequest(request); return true; } }; public interface OnInflateFinishedListener { void onInflateFinished(@NonNull View view, @LayoutRes int resid, @Nullable ViewGroup parent); } private static class InflateRequest { AsyncLayoutInflatePlus inflater; ViewGroup parent; int resid; View view; OnInflateFinishedListener callback; InflateRequest() { } } private static class Dispather { //获得当前CPU的核心数 private static final int CPU_COUNT = Runtime.getRuntime().availableProcessors(); //设置线程池的核心线程数2-4之间,但是取决于CPU核数 private static final int CORE_POOL_SIZE = Math.max(2, Math.min(CPU_COUNT - 1, 4)); //设置线程池的最大线程数为 CPU核数 * 2 + 1 private static final int MAXIMUM_POOL_SIZE = CPU_COUNT * 2 + 1; //设置线程池空闲线程存活时间30s private static final int KEEP_ALIVE_SECONDS = 30; private static final ThreadFactory sThreadFactory = new ThreadFactory() { private final AtomicInteger mCount = new AtomicInteger(1); public Thread newThread(Runnable r) { return new Thread(r, "AsyncLayoutInflatePlus #" + mCount.getAndIncrement()); } }; //LinkedBlockingQueue 默认构造器，队列容量是Integer.MAX_VALUE private static final BlockingQueue sPoolWorkQueue = new LinkedBlockingQueue(); /** * An {@link Executor} that can be used to execute tasks in parallel. */ public static final ThreadPoolExecutor THREAD_POOL_EXECUTOR; static { Log.i(TAG, "static initializer: " + " CPU_COUNT = " + CPU_COUNT + " CORE_POOL_SIZE = " + CORE_POOL_SIZE + " MAXIMUM_POOL_SIZE = " + MAXIMUM_POOL_SIZE); ThreadPoolExecutor threadPoolExecutor = new ThreadPoolExecutor( CORE_POOL_SIZE, MAXIMUM_POOL_SIZE, KEEP_ALIVE_SECONDS, TimeUnit.SECONDS, sPoolWorkQueue, sThreadFactory); threadPoolExecutor.allowCoreThreadTimeOut(true); THREAD_POOL_EXECUTOR = threadPoolExecutor; } public void enqueue(InflateRequest request) { THREAD_POOL_EXECUTOR.execute((new InflateRunnable(request))); } } private static class BasicInflater extends LayoutInflater { private static final String[] sClassPrefixList = { "android.widget.", "android.webkit.", "android.app." }; BasicInflater(Context context) { super(context); if (context instanceof AppCompatActivity) { // 手动setFactory2，兼容AppCompatTextView等控件 AppCompatDelegate appCompatDelegate = ((AppCompatActivity) context).getDelegate(); if (appCompatDelegate instanceof LayoutInflater.Factory2) { LayoutInflaterCompat.setFactory2(this, (LayoutInflater.Factory2) appCompatDelegate); } } } @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 InflateRunnable implements Runnable { private InflateRequest request; private boolean isRunning; public InflateRunnable(InflateRequest request) { this.request = request; } @Override public void run() { isRunning = true; 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(); } public boolean isRunning() { return isRunning; } } 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 cancel() { mHandler.removeCallbacksAndMessages(null); mHandlerCallback = null; }} 总结
本文介绍了通过异步的方式进行布局加载，缓解了主线程的压力。同时也介绍了AsyncLayoutInflate的实现原理以及如何定制自己的AsyncLayoutInflate。本文的定制方式仅仅只是作为一个参考，具体的实现方式可以根据自己项目的实际情况来定制
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