Android中异步加载布局的小能手_AsyncLayoutIn

作者: dashingqi | 来源:发表于2020-03-12 21:41 被阅读0次

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

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

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

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

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

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

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

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

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

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View

This 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。

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。

Android中异步加载布局的小能手_AsyncLayoutIn

本文主要从如下几点学习AsyncLayoutInflater

AsyncLayoutInflater是啥

官方源码定义

AsyncLayoutInflater代码实操

AsyncLayoutInflater源码解析

AsyncLayoutInflater的构造方法

AsyncLayoutInflater的inflate方法

AsyncLayoutInflater中的InflateThread类

AsyncLayoutInflater中的InflateRequest类

AsyncLayoutInflater的BasicInflater类

AsyncLayoutInflater的Callback

AsyncLayoutInflater的问题

同样看源码定义

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。

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。

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