Android Presentation实现双屏异显

public Presentation(Context outerContext, Display display, int theme) {
 super(createPresentationContext(outerContext, display, theme), theme, false);
 
 mDisplay = display;
 mDisplayManager = (DisplayManager)getContext().getSystemService(DISPLAY_SERVICE);
 
 final Window w = getWindow();
 final WindowManager.LayoutParams attr = w.getAttributes();
 attr.token = mToken;
 w.setAttributes(attr);
 w.setGravity(Gravity.FILL);
 w.setType(TYPE_PRESENTATION);
 setCanceledOnTouchOutside(false);
 }

private static Context createPresentationContext(
 Context outerContext, Display display, int theme) {
 //首先判断传入的context和display是否为空，为空则抛出异常
 if (outerContext == null) {
 throw new IllegalArgumentException("outerContext must not be null");
 }
 if (display == null) {
 throw new IllegalArgumentException("display must not be null");
 }
 
 Context displayContext = outerContext.createDisplayContext(display);
 
 //这里是对它的主题的判断，为0即为默认主题
 if (theme == 0) {
 TypedValue outValue = new TypedValue();
 displayContext.getTheme().resolveAttribute(
  com.android.internal.R.attr.presentationTheme, outValue, true);
 theme = outValue.resourceId;
 }
 
 // Derive the display's window manager from the outer window manager.
 // We do this because the outer window manager have some extra information
 // such as the parent window, which is important if the presentation uses
 // an application window type.
 final WindowManagerImpl outerWindowManager =
 (WindowManagerImpl)outerContext.getSystemService(WINDOW_SERVICE);
 final WindowManagerImpl displayWindowManager =
 outerWindowManager.createPresentationWindowManager(displayContext);
 
 //因为ContextThemeWrapper的父类是我们的Context
 //所以这里最终返回的就是Presentation给我们创建好的Context
 return new ContextThemeWrapper(displayContext, theme) {
 
 //在这个方法中又返回的是Object对象
 @Override
 public Object getSystemService(String name) {
 if (WINDOW_SERVICE.equals(name)) {
  return displayWindowManager;
  //如果和这个传入的name相同的话返回的就是上面windowManager创建出来的WindowManager的一个具体实现
 }
 //否则就返回的是Context这个抽象类中的一种服务类型
 return super.getSystemService(name);
 }
 };
 }

private final DisplayListener mDisplayListener = new DisplayListener() {
 @Override
 public void onDisplayAdded(int displayId) {
 }
 
 @Override
 public void onDisplayRemoved(int displayId) {
 if (displayId == mDisplay.getDisplayId()) {
 handleDisplayRemoved();
 }
 }
 
 @Override
 public void onDisplayChanged(int displayId) {
 if (displayId == mDisplay.getDisplayId()) {
 handleDisplayChanged();
 }
 }
 };

private void handleDisplayChanged() {
 onDisplayChanged();
 
 // We currently do not support configuration changes for presentations
 // (although we could add that feature with a bit more work).
 // If the display metrics have changed in any way then the current configuration
 // is invalid and the application must recreate the presentation to get
 // a new context.
 if (!isConfigurationStillValid()) {
 Log.i(TAG, "Presentation is being dismissed because the "
  + "display metrics have changed since it was created.");
 cancel();
 }
 }

@Override
 protected void onStart() {
 super.onStart();
 mDisplayManager.registerDisplayListener(mDisplayListener, mHandler);
 
 // Since we were not watching for display changes until just now, there is a
 // chance that the display metrics have changed. If so, we will need to
 // dismiss the presentation immediately. This case is expected
 // to be rare but surprising, so we'll write a log message about it.
 if (!isConfigurationStillValid()) {
 Log.i(TAG, "Presentation is being dismissed because the "
  + "display metrics have changed since it was created.");
 mHandler.sendEmptyMessage(MSG_CANCEL);
 }
 }