android window(二)从getSystemService到WindowManagerGlobal

在Activity调用getSystemService(WINDOW_SERVICE) 调用的是父类ContextThemeWrapper

package android.view;
public class ContextThemeWrapper extends ContextWrapper {
  @Override
    public Object getSystemService(String name) {
        if (LAYOUT_INFLATER_SERVICE.equals(name)) {
            if (mInflater == null) {
                mInflater = LayoutInflater.from(getBaseContext()).cloneInContext(this);
            }
            return mInflater;
        }
        return getBaseContext().getSystemService(name);
    }
}

这里getBaseContext返回是context的实现类ContextImpl

//ContextImpl
@Override
public Object getSystemService(String name) {
    return SystemServiceRegistry.getSystemService(this, name);
}

//SystemServiceRegistry
public static Object getSystemService(ContextImpl ctx, String name) {
    ServiceFetcher<?> fetcher = SYSTEM_SERVICE_FETCHERS.get(name);
    return fetcher != null ? fetcher.getService(ctx) : null;
}

SYSTEM_SERVICE_FETCHERS是一个map，key为WINDOW_SERVICE时，对应的value是什么？

ContextImpl.java 的源码

208  class ContextImpl extends Context {
//...
628        registerService(WINDOW_SERVICE, new ServiceFetcher() {
629                Display mDefaultDisplay;
630                public Object getService(ContextImpl ctx) {
631                    Display display = ctx.mDisplay;
632                    if (display == null) {
633                        if (mDefaultDisplay == null) {
634                            DisplayManager dm = (DisplayManager)ctx.getOuterContext().
635                                    getSystemService(Context.DISPLAY_SERVICE);
636                            mDefaultDisplay = dm.getDisplay(Display.DEFAULT_DISPLAY);
637                        }
638                        display = mDefaultDisplay;
639                    }
640                    return new WindowManagerImpl(display);
641                }});

1829    @Override
1830    public Object getSystemService(String name) {
1831        ServiceFetcher fetcher = SYSTEM_SERVICE_MAP.get(name);
1832        return fetcher == null ? null : fetcher.getService(this);
1833    }
//...
}

WindowManagerImpl.java

public final class WindowManagerImpl implements WindowManager {
    private final WindowManagerGlobal mGlobal = WindowManagerGlobal.getInstance();
    private final Display mDisplay;
    private final Window mParentWindow;
    //...
    public WindowManagerImpl createLocalWindowManager(Window parentWindow) {
        return new WindowManagerImpl(mDisplay, parentWindow);
    }

    public WindowManagerImpl createPresentationWindowManager(Display display) {
        return new WindowManagerImpl(display, mParentWindow);
    }

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

    @Override
    public void updateViewLayout(View view, ViewGroup.LayoutParams params) {
        mGlobal.updateViewLayout(view, params);
    }

    @Override
    public void removeView(View view) {
        mGlobal.removeView(view, false);
    }

    @Override
    public void removeViewImmediate(View view) {
        mGlobal.removeView(view, true);
    }

    @Override
    public Display getDefaultDisplay() {
        return mDisplay;
    }
}

WindowManager.java

public interface WindowManager extends ViewManager {
//...
}

ViewManager.java

public interface ViewManager
{
    public void addView(View view, ViewGroup.LayoutParams params);
    public void updateViewLayout(View view, ViewGroup.LayoutParams params);
    public void removeView(View view);
}

WindowManager的addView的过程，WindowManager是个接口，它的实现类是WindowManagerImpl类，而WindowManagerImpl又把相关逻辑交给了WindowManagerGlobal处理。WindowManagerGlobal是个单例类，它在进程中只存在一个实例，是它内部的addView方法最终创建了我们的核心类ViewRootImpl。

可以看到这里的WindowManagerImpl 的主要功能都是通过WindowManagerGlobal来实现的

WindowManagerGlobal.java

public final class WindowManagerGlobal {
    private static final String TAG = "WindowManager";

       //...
    private static WindowManagerGlobal sDefaultWindowManager;
    private static IWindowManager sWindowManagerService;
    private static IWindowSession sWindowSession;

    private final Object mLock = new Object();

    private final ArrayList<View> mViews = new ArrayList<View>();
    private final ArrayList<ViewRootImpl> mRoots = new ArrayList<ViewRootImpl>();
    private final ArrayList<WindowManager.LayoutParams> mParams =
            new ArrayList<WindowManager.LayoutParams>();
    private final ArraySet<View> mDyingViews = new ArraySet<View>();

    private Runnable mSystemPropertyUpdater;

    private WindowManagerGlobal() {
    }

    public static WindowManagerGlobal getInstance() {
        synchronized (WindowManagerGlobal.class) {
            if (sDefaultWindowManager == null) {
                sDefaultWindowManager = new WindowManagerGlobal();
            }
            return sDefaultWindowManager;
        }
    }

    public static IWindowManager getWindowManagerService() {
        synchronized (WindowManagerGlobal.class) {
            if (sWindowManagerService == null) {
                sWindowManagerService = IWindowManager.Stub.asInterface(
                        ServiceManager.getService("window"));
            }
            return sWindowManagerService;
        }
    }

    public static IWindowSession getWindowSession() {
        synchronized (WindowManagerGlobal.class) {
            if (sWindowSession == null) {
                try {
                    InputMethodManager imm = InputMethodManager.getInstance();
                    IWindowManager windowManager = getWindowManagerService();
                    sWindowSession = windowManager.openSession(
                            new IWindowSessionCallback.Stub() {
                                @Override
                                public void onAnimatorScaleChanged(float scale) {
                                    ValueAnimator.setDurationScale(scale);
                                }
                            },
                            imm.getClient(), imm.getInputContext());
                    ValueAnimator.setDurationScale(windowManager.getCurrentAnimatorScale());
                } catch (RemoteException e) {
                    Log.e(TAG, "Failed to open window session", e);
                }
            }
            return sWindowSession;
        }
    }

    public static IWindowSession peekWindowSession() {
        synchronized (WindowManagerGlobal.class) {
            return sWindowSession;
        }
    }

    public String[] getViewRootNames() {
        synchronized (mLock) {
            final int numRoots = mRoots.size();
            String[] mViewRoots = new String[numRoots];
            for (int i = 0; i < numRoots; ++i) {
                mViewRoots[i] = getWindowName(mRoots.get(i));
            }
            return mViewRoots;
        }
    }

    public View getRootView(String name) {
        synchronized (mLock) {
            for (int i = mRoots.size() - 1; i >= 0; --i) {
                final ViewRootImpl root = mRoots.get(i);
                if (name.equals(getWindowName(root))) return root.getView();
            }
        }

        return null;
    }

    public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
       //...
            root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);

            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);
        }

        // do this last because it fires off messages to start doing things
        try {
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
            // BadTokenException or InvalidDisplayException, clean up.
            synchronized (mLock) {
                final int index = findViewLocked(view, false);
                if (index >= 0) {
                    removeViewLocked(index, true);
                }
            }
            throw e;
        }
    }

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

        final WindowManager.LayoutParams wparams = (WindowManager.LayoutParams)params;

        view.setLayoutParams(wparams);

        synchronized (mLock) {
            int index = findViewLocked(view, true);
            ViewRootImpl root = mRoots.get(index);
            mParams.remove(index);
            mParams.add(index, wparams);
            root.setLayoutParams(wparams, false);
        }
    }

    public void removeView(View view, boolean immediate) {
        if (view == null) {
            throw new IllegalArgumentException("view must not be null");
        }

        synchronized (mLock) {
            int index = findViewLocked(view, true);
            View curView = mRoots.get(index).getView();
            removeViewLocked(index, immediate);
            if (curView == view) {
                return;
            }

            throw new IllegalStateException("Calling with view " + view
                    + " but the ViewAncestor is attached to " + curView);
        }
    }

    public void closeAll(IBinder token, String who, String what) {
     //...
    }

    private void removeViewLocked(int index, boolean immediate) {
        ViewRootImpl root = mRoots.get(index);
        View view = root.getView();

        if (view != null) {
            InputMethodManager imm = InputMethodManager.getInstance();
            if (imm != null) {
                imm.windowDismissed(mViews.get(index).getWindowToken());
            }
        }
        boolean deferred = root.die(immediate);
        if (view != null) {
            view.assignParent(null);
            if (deferred) {
                mDyingViews.add(view);
            }
        }
    }

    void doRemoveView(ViewRootImpl root) {
        synchronized (mLock) {
            final int index = mRoots.indexOf(root);
            if (index >= 0) {
                mRoots.remove(index);
                mParams.remove(index);
                final View view = mViews.remove(index);
                mDyingViews.remove(view);
            }
        }
        if (HardwareRenderer.sTrimForeground && HardwareRenderer.isAvailable()) {
            doTrimForeground();
        }
    }

    private int findViewLocked(View view, boolean required) {
        final int index = mViews.indexOf(view);
        if (required && index < 0) {
            throw new IllegalArgumentException("View=" + view + " not attached to window manager");
        }
        return index;
    }

    //...
}

每个应用进程，仅有一个 sWindowSession 对象，它对应了 WmS 中的 Session 子类，WmS 为每一个应用进程分配一个 Session 对象。WindowState 类有一个 IWindow mClient 参数，是由 Session 调用 addToDisplay 传递过来的，对应了 ViewRootImpl 中的 W 类的实例。

WindowManagerGlobal的addView里面初始化了

  public void addView(View view, ViewGroup.LayoutParams params,
            Display display, Window parentWindow) {
       //...
            root = new ViewRootImpl(view.getContext(), display);

            view.setLayoutParams(wparams);

            mViews.add(view);
            mRoots.add(root);
            mParams.add(wparams);
        }

        // do this last because it fires off messages to start doing things
        try {
            root.setView(view, wparams, panelParentView);
        } catch (RuntimeException e) {
            // BadTokenException or InvalidDisplayException, clean up.
            synchronized (mLock) {
                final int index = findViewLocked(view, false);
                if (index >= 0) {
                    removeViewLocked(index, true);
                }
            }
            throw e;
        }
    }

WindowManagerGlobal的窗口管理:

WindowManager的总结

经过前文的分析，相信读者对WindowManager的工作原理有了深入的认识。

• 鉴于窗口布局和控件布局的一致性，WindowManager继承并实现了接口ViewManager。

• 使用者可以通过Context.getSystemService(Context.WINDOW_SERVICE)来获取一个WindowManager的实例。这个实例的真实类型是WindowManagerImpl。WindowManagerImpl一旦被创建就确定了通过它所创建的窗口所属哪块屏幕？哪个父窗口？

• WindowManagerImpl除了保存了窗口所属的屏幕以及父窗口以外，没有任何实质性的工作。窗口的管理都交由WindowManagerGlobal的实例完成。

• WindowManagerGlobal在一个进程中只有一个实例。

• WindowManagerGlobal在3个数组中统一管理整个进程中的所有窗口的信息。这些信息包括控件、布局参数以及ViewRootImpl三个元素。

• 除了管理窗口的上述3个元素以外，WindowManagerGlobal将窗口的创建、销毁与布局更新等任务交付给了ViewRootImpl完成。

说明 在实际的应用开发过程中，有时会在logcat的输出中遇到有关WindowLeaked的异常输出。WindowLeaked异常发生与WindowManagerGlobal中，其原因是Activity在destroy之前没有销毁其附属窗口，如对话框、弹出菜单等。

如此看来，WindowManager的实现仍然是很轻量的。窗口的创建、销毁与布局更新都指向了一个组件：ViewRootImpl。