本文主要从如下几点学习AsyncLayoutInflater
- AsyncLayoutInfalter是啥
- AsyncLayoutInflater代码实操
- AsyncLayoutInflater的源码分析
- AsyncLayoutInflater的问题
AsyncLayoutInflater是啥
官方源码定义
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如下
Helper class for inflating layouts asynchronously //用于异步加载布局的帮助类
AsyncLayoutInflater代码实操
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代码如下
new AsyncLayoutInflater(this).inflate(R.layout.activity_main, null, new AsyncLayoutInflater.OnInflateFinishedListener() { @Override public void onInflateFinished(@NonNull View view, int resid, @Nullable ViewGroup parent) { Log.d(TAG, "currentThread = " + Thread.currentThread().getName()); setContentView(view); } });
AsyncLayoutInflater源码解析
AsyncLayoutInflater的构造方法
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代码如下
public AsyncLayoutInflater(@NonNull Context context) { //创建BasicInflater对象，BasicInflater继承至 LayoutInflater mInflater = new BasicInflater(context); //创建一个Handler对象，目的是线程的切换，从布局加载的工作线程切换到主线程中。 mHandler = new Handler(mHandlerCallback); //创建一个InflateThread对象，该类是继承至Thread类， mInflateThread = InflateThread.getInstance(); }
AsyncLayoutInflater的inflate方法
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代码如下
@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!"); } // 构建InflateRequest对象，将resid、parent、callback等变量存储到这个变量中。 InflateRequest request = mInflateThread.obtainRequest(); request.inflater = this; request.resid = resid; request.parent = parent; request.callback = callback; // 然后将带有参数的InflateRequest对象，通过Inflatethread类中的enqueue方法保存到ArrayBlockingQueue队列中 mInflateThread.enqueue(request); }
AsyncLayoutInflater中的InflateThread类
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代码如下
// InflateThread是AsyncLayoutInfalter类中的一个静态内部类 private static class InflateThread extends Thread { private static final InflateThread sInstance; // 当类加载的时候，会初始化该类并且开启线程 static { sInstance = new InflateThread(); sInstance.start(); } //对外提供获取实例的方法 public static InflateThread getInstance() { return sInstance; } //生产者-消费者的模型，阻塞队列 private ArrayBlockingQueue<InflateRequest> mQueue = new ArrayBlockingQueue<>(10); //使用了对象池，来缓存创建的InflateRequest对象，防止重复创建 private SynchronizedPool<InflateRequest> mRequestPool = new SynchronizedPool<>(10); public void runInner() { InflateRequest request; try { //从队列中取出一个请求， request = mQueue.take(); } catch (InterruptedException ex) { // Odd, just continue Log.w(TAG, ex); return; } try { //LayoutInfalter加载view的操作 //获取到View对象 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); } //无论inflate方法的失败或者成功，都将request发送到主线程中。 Message.obtain(request.inflater.mHandler, 0, request) .sendToTarget(); } @Override public void run() { //死循环 while (true) { runInner(); } } //主要创建一个InflateRequest对象 public InflateRequest obtainRequest() { //先从对象缓存池中查询 InflateRequest obj = mRequestPool.acquire(); //如果当前InflateRequest对象没有创建过，就创建一个 if (obj == null) { obj = new InflateRequest(); } //否则的话就将当前内存中存在的返回； return obj; } //将对象缓存池中的对象数据清空，方便对象的复用。 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请求中的request存储到队列中 public void enqueue(InflateRequest request) { try { mQueue.put(request); } catch (InterruptedException e) { throw new RuntimeException( "Failed to enqueue async inflate request", e); } } }
AsyncLayoutInflater中的InflateRequest类
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代码如下
//该类主要是携带数据，赋给Message.obj变量，通过Message将数据发送到主线程中 private static class InflateRequest { AsyncLayoutInflater inflater; ViewGroup parent; int resid; View view; OnInflateFinishedListener callback; InflateRequest() { } }
AsyncLayoutInflater的BasicInflater类
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代码如下
//该类是继承至LayoutInflater //重写了onCreateView 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 { //在onCreateView中优先加载 android.widget.", "android.webkit.","android.app."中的控件，之后在按照常规的加载方式去加载 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); } }
AsyncLayoutInflater的Callback
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代码如下
private Callback mHandlerCallback = new Callback() { @Override public boolean handleMessage(Message msg) { //通过Handler从Message中获取InflateRequest中的数据带到主线程 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); //置空InflateRequest中携带的数据 mInflateThread.releaseRequest(request); return true; } };
AsyncLayoutInflater的问题
同样看源码定义
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定义如下
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. // 1. 对于异步加载的布局需要它的父View的generateLayoutParams(AttributeSet attrs)方法是线程安全的。 // 2. 所有被创建的View不能在内部创建Handler或者是调用Looper.myLooper()方法。 // 如果使用AsynclayoutInflater.inflate()的方法异步加载失败，不管是什么原因，都会会退到主线程中就加载布局。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. // 3. 异步加载布局获取的View没有添加到父View中，因为源码中request.inflater.mInflater.inflate( // request.resid, request.parent, false);是这样调用去加载布局的 attachToRoot 为 false // 所以如果希望被添加到父View中，需要在onInflateFinishedListener方法中去手动添加ViewThis inflater does not support setting a {@link LayoutInflater.Factory} nor {@link LayoutInflater.Factory2}. Similarly it does not support inflating layouts that contain fragments. // 4. 不支持设置LayoutInflater.Factory和Factory2 // 5. 不支持加载包含Fragment的布局
为什么会有这些问题
针对第一点：对于异步加载的布局需要它的父View(ViewGroup)的generateLayoutParams(AttributeSet attrs)方法是线程安全的。
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看ViewGroup的generateLayoutParams(AttributeSet attrs)f方法（注意参数哟，ViewGroup中有很多同名的重载方法）
public LayoutParams generateLayoutParams(AttributeSet attrs) { return new LayoutParams(getContext(), attrs); } // 可以看到，直接new了一个对象出来，如果是在非线程安全的情况下去调用，会创建多个对象。
针对第二点:所有被创建的View不能在内部创建Handler或者是调用Looper.myLooper()方法。
- 因为是异步加载，在子线程中如果使用Handler必须在同线程下创建一个looper对象，不然会报错的。同样Looper.myLooper是获取同线程下的looper对象，你的有才能用，才能获取。
