Android子线程其实也可以刷新UI。。。。

来源：互联网发布：win7下怎么安装ubuntu 编辑：程序博客网时间：2024/04/29 11:32

如果你在网上搜索CalledFromWrongThreadException：Only the original thread that created a view hierarchy can touch its views. 那么你肯定能看到很多文章说android里子线程不能刷新UI。这句话不能说错，只是有些不太严谨。其实线程能否刷新UI的关键在于ViewRoot是否属于该线程。

首先，CalledFromWrongThreadException这个异常是有下面的代码抛出的：

    void checkThread() {         if (mThread != Thread.currentThread()) {             throw new CalledFromWrongThreadException(                     "Only the original thread that created a view hierarchy can touch its views.");         } }

该段代码出自 framework/base/core/java/android/view/ViewRoot.java

其次，看看RootView的构造函数：

public ViewRoot(Context context) {     super();       if (MEASURE_LATENCY && lt == null) {         lt = new LatencyTimer(100, 1000);     }       // For debug only     //++sInstanceCount;       // Initialize the statics when this class is first instantiated. This is     // done here instead of in the static block because Zygote does not     // allow the spawning of threads.     getWindowSession(context.getMainLooper());           mThread = Thread.currentThread();     mLocation = new WindowLeaked(null);     mLocation.fillInStackTrace();     mWidth = -1;     mHeight = -1;     mDirty = new Rect();     mTempRect = new Rect();     mVisRect = new Rect();     mWinFrame = new Rect();     mWindow = new W(this, context);     mInputMethodCallback = new InputMethodCallback(this);     mViewVisibility = View.GONE;     mTransparentRegion = new Region();     mPreviousTransparentRegion = new Region();     mFirst = true; // true for the first time the view is added     mAdded = false;     mAttachInfo = new View.AttachInfo(sWindowSession, mWindow, this, this);     mViewConfiguration = ViewConfiguration.get(context);     mDensity = context.getResources().getDisplayMetrics().densityDpi; }

最后，我们看看ViewRoot.checkThread的调用顺序：

com.david.test.helloworld.MainActivity$TestThread2.run
  -> android.widget.TextView.setText
    -> android.widget.TextView.checkForRelayout
      -> android.view.View.invalidate
        -> android.view.ViewGroup.invalidateChild
          -> android.view.ViewRoot.invalidateChildInParent
            -> android.view.ViewRoot.invalidateChild
              -> android.view.ViewRoot.checkThread

到这里相信网友已经明白CalledFromWrongThreadException为什么出现了。那到底非主线程以外的线程能否刷新UI呢？呵呵，答案当然是能，前提条件是它要拥有自己的ViewRoot。如果你要直接创建ViewRoot的实例的话，你会失望的发现不能找到这个类。那么我们要如何做呢？让我们用实例来说说吧，代码如下：

   class TestThread1 extends Thread{               @Override               public void run() {                      Looper.prepare();                                             TextView tx = new TextView(MainActivity.this);                      tx.setText("test11111111111111111");                                                    WindowManager wm = MainActivity.this.getWindowManager();                   WindowManager.LayoutParams params = new WindowManager.LayoutParams( 250, 250, 200, 200, WindowManager.LayoutParams.FIRST_SUB_WINDOW,                                WindowManager.LayoutParams.TYPE_TOAST,PixelFormat.OPAQUE);                                           wm.addView(tx, params);                                          Looper.loop();               }     }

MainActivity是建立android工程时生成的入口类，TestThread1是MainActivity的内部类。感兴趣的话，试试吧！看看是不是在屏幕上看到了"test11111111111111111"？

最后，说说那里创建了ViewRoot，这里：wm.addView(tx, params)。还是看看具体流程吧：

WindowManagerImpl.addView(View view, ViewGroup.LayoutParams params)

-> WindowManagerImpl.addView(View view, ViewGroup.LayoutParams params, boolean nest)，奥妙就在这里，具体看看代码吧！

private void addView(View view, ViewGroup.LayoutParams params, boolean nest)     {         if (Config.LOGV) Log.v("WindowManager", "addView view=" + view);            if (!(params instanceof WindowManager.LayoutParams)) {             throw new IllegalArgumentException(                     "Params must be WindowManager.LayoutParams");         }            final WindowManager.LayoutParams wparams                 = (WindowManager.LayoutParams)params;                   ViewRoot root;         View panelParentView = null;                   synchronized (this) {             // Here's an odd/questionable case: if someone tries to add a             // view multiple times, then we simply bump up a nesting count             // and they need to remove the view the corresponding number of             // times to have it actually removed from the window manager.             // This is useful specifically for the notification manager,             // which can continually add/remove the same view as a             // notification gets updated.             int index = findViewLocked(view, false);             if (index >= 0) {                 if (!nest) {                     throw new IllegalStateException("View " + view                             + " has already been added to the window manager.");                 }                 root = mRoots[index];                 root.mAddNesting++;                 // Update layout parameters.                 view.setLayoutParams(wparams);                 root.setLayoutParams(wparams, true);                 return;             }                           // If this is a panel window, then find the window it is being             // attached to for future reference.             if (wparams.type >= WindowManager.LayoutParams.FIRST_SUB_WINDOW &&                     wparams.type <= WindowManager.LayoutParams.LAST_SUB_WINDOW) {                 final int count = mViews != null ? mViews.length : 0;                 for (int i=0; i<count; i++) {                     if (mRoots[i].mWindow.asBinder() == wparams.token) {                         panelParentView = mViews[i];                     }                 }             }                           root = new ViewRoot(view.getContext());             root.mAddNesting = 1;                view.setLayoutParams(wparams);                           if (mViews == null) {                 index = 1;                 mViews = new View[1];                 mRoots = new ViewRoot[1];                 mParams = new WindowManager.LayoutParams[1];             } else {                 index = mViews.length + 1;                 Object[] old = mViews;                 mViews = new View[index];                 System.arraycopy(old, 0, mViews, 0, index-1);                 old = mRoots;                 mRoots = new ViewRoot[index];                 System.arraycopy(old, 0, mRoots, 0, index-1);                 old = mParams;                 mParams = new WindowManager.LayoutParams[index];                 System.arraycopy(old, 0, mParams, 0, index-1);             }             index--;                mViews[index] = view;             mRoots[index] = root;             mParams[index] = wparams;         }         // do this last because it fires off messages to start doing things         root.setView(view, wparams, panelParentView); }

出自：frameworks/base/core/java/android/view/WindowManagerImpl.java

Ok，相信到了这里，大家都已经明白了：子线程是能够刷新UI的！！！

原文出处：http://blog.csdn.net/imyfriend/article/details/6877959

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