Android子线程真的不能更新UI么(2)

　　最终通过checkThread形成了这个异常。说到底，非UI线程是可以刷新UI的呀，前提是它要拥有自己的ViewRoot。如果想直接创建ViewRoot实例，你会发现找不到这个类。那怎么做呢？通过WindowManager。

class NonUiThread extends Thread{
      @Override
      public void run() {
        Looper.prepare();
        TextView tx = new TextView(MainActivity.this);
        tx.setText("non-UiThread update textview");
 
        WindowManager windowManager = MainActivity.this.getWindowManager();
        WindowManager.LayoutParams params = new WindowManager.LayoutParams(
            200, 200, 200, 200, WindowManager.LayoutParams.FIRST_SUB_WINDOW,
                WindowManager.LayoutParams.TYPE_TOAST,PixelFormat.OPAQUE);
        windowManager.addView(tx, params);
        Looper.loop();
    }
 }

　　就是通过windowManager.addView创建了ViewRoot，WindowManagerImpl.java中的addView方法：

@Override
public void addView(@NonNull View view, @NonNull ViewGroup.LayoutParams params) {
    applyDefaultToken(params);
    mGlobal.addView(view, params, mDisplay, mParentWindow);
}

private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();

　　mGlobal是一个WindowManagerGlobal实例，代码在 frameworks/base/core/java/android/view/WindowManagerGlobal.java中，具体实现如下：

public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }
        if (display == null) {
            throw new IllegalArgumentException("display must not be null");
        }
        if (!(params instanceof WindowManager.LayoutParams)) {
            throw new IllegalArgumentException("Params must be WindowManager.LayoutParams");
        }

final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams) params;
        if (parentWindow != null) {
            parentWindow.adjustLayoutParamsForSubWindow(wparams);
        } else {
            // If there's no parent, then hardware acceleration for this view is
            // set from the application's hardware acceleration setting.
            final Context context = view.getContext();
            if (context != null
                    && (context.getApplicationInfo().flags
                            & ApplicationInfo.FLAG_HARDWARE_ACCELERATED) != 0) {
                wparams.flags |= WindowManager.LayoutParams.FLAG_HARDWARE_ACCELERATED;
            }
        }

ViewRootImpl root;
        View panelParentView = null;

synchronized (mLock) {
            // Start watching for system property changes.
            if (mSystemPropertyUpdater == null) {
                mSystemPropertyUpdater = new Runnable() {
                    @Override public void run() {
                        synchronized (mLock) {
                            for (int i = mRoots.size() - 1; i >= 0; --i) {
                                mRoots.get(i).loadSystemProperties();
                            }
                        }
                    }
                };
                SystemProperties.addChangeCallback(mSystemPropertyUpdater);
            }