Android里子线程真的不能刷新UI吗？

 

       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。

       让我们一起看看代码吧！

       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！！！