欢迎您访问程序员文章站本站旨在为大家提供分享程序员计算机编程知识!
您现在的位置是: 首页  >  IT编程

Android里子线程真的不能刷新UI吗?实例证明

程序员文章站 2022-06-15 21:17:45
原文链接:http://blog.csdn.net/imyfriend/article/details/6877959原文写的很优秀,格式不敢恭维,博主也一直没有更新,所以改下格式!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....

原文链接:Android里子线程真的不能刷新UI吗?
原文写的很优秀,格式不敢恭维,示例代码也有bug,博主也一直没有更新,所以我改了下格式,并且修改了子线程刷新UI的示例代码!

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:(运行环境:Android studio 3.4.0 sdk 28 测试机:vivo 6.0.1,不需要在AndroidManifest.xml加任何权限)

 public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        new TestThread1().start();
    }
    
    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
            );

            Dialog dialog = new Dialog(MainActivity.this);
            dialog.addContentView(tx, params);
            dialog.show();
            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!!!

本文地址:https://blog.csdn.net/zhangjin1120/article/details/110213639

相关标签: Android技术积累