1、簡介
WindowManagerService（WMS）是Android中很重要的一個服務，主要的職責是與ActivityManagerService（AMS）交互以管理Window，與InputManagerService（IMS）交互以派發事件。分析WMS，先從下面的類圖開始吧，看看相關的類都有哪些，主要的類包括WindowManagerService、WindowManagerImpl、PhoneWindowManager、WindowManagerGlobal、ViewRootImpl等。
2、啓動
WMS是在SystemServer中啓動的，下面的時序圖展示了WMS及AMS、IMS的啓動過程，以及它們是如何建立聯繫的。
3、addView
addView是一個常用的方法，流程圖如下。從WindowManagerImpl開始，經WindowManagerGlobal、ViewRootImpl、Session，最後到WindowManagerService結束。在WMS的addWindow中，首先要檢查權限，然後通過WindowToken、WindowState完成。
4、Layer
Window有三種類型，Application Window、Sub Window和System Window，這些Window有不同的Type，用int表示， Application Window從1到99，Sub Window從1000到1999，System Window從2000到2999，它們在WindowManager中定義，代碼如下所示。
public static final int FIRST_APPLICATION_WINDOW = 1;
public static final int TYPE_BASE_APPLICATION = 1;
public static final int TYPE_APPLICATION = 2;
public static final int TYPE_APPLICATION_STARTING = 3;
public static final int TYPE_DRAWN_APPLICATION = 4;
public static final int LAST_APPLICATION_WINDOW = 99;
public static final int FIRST_SUB_WINDOW = 1000;
public static final int TYPE_APPLICATION_PANEL = FIRST_SUB_WINDOW;
public static final int TYPE_APPLICATION_MEDIA = FIRST_SUB_WINDOW + 1;
public static final int TYPE_APPLICATION_SUB_PANEL = FIRST_SUB_WINDOW + 2;
public static final int TYPE_APPLICATION_ATTACHED_DIALOG = FIRST_SUB_WINDOW + 3;
public static final int TYPE_APPLICATION_MEDIA_OVERLAY = FIRST_SUB_WINDOW + 4;
public static final int TYPE_APPLICATION_ABOVE_SUB_PANEL = FIRST_SUB_WINDOW + 5;
public static final int LAST_SUB_WINDOW = 1999;
public static final int FIRST_SYSTEM_WINDOW = 2000;
public static final int TYPE_STATUS_BAR = FIRST_SYSTEM_WINDOW;
public static final int TYPE_SEARCH_BAR = FIRST_SYSTEM_WINDOW+1;
public static final int TYPE_PHONE = FIRST_SYSTEM_WINDOW+2;
public static final int TYPE_SYSTEM_ALERT = FIRST_SYSTEM_WINDOW+3;
public static final int TYPE_KEYGUARD = FIRST_SYSTEM_WINDOW+4;
public static final int TYPE_TOAST = FIRST_SYSTEM_WINDOW+5;
public static final int TYPE_SYSTEM_OVERLAY = FIRST_SYSTEM_WINDOW+6;
public static final int TYPE_PRIORITY_PHONE = FIRST_SYSTEM_WINDOW+7;
public static final int TYPE_SYSTEM_DIALOG = FIRST_SYSTEM_WINDOW+8;
public static final int TYPE_KEYGUARD_DIALOG = FIRST_SYSTEM_WINDOW+9;
public static final int TYPE_SYSTEM_ERROR = FIRST_SYSTEM_WINDOW+10;
public static final int TYPE_INPUT_METHOD = FIRST_SYSTEM_WINDOW+11;
public static final int TYPE_INPUT_METHOD_DIALOG= FIRST_SYSTEM_WINDOW+12;
public static final int TYPE_WALLPAPER = FIRST_SYSTEM_WINDOW+13;
public static final int TYPE_STATUS_BAR_PANEL = FIRST_SYSTEM_WINDOW+14;
public static final int TYPE_SECURE_SYSTEM_OVERLAY = FIRST_SYSTEM_WINDOW+15;
public static final int TYPE_DRAG = FIRST_SYSTEM_WINDOW+16;
public static final int TYPE_STATUS_BAR_SUB_PANEL = FIRST_SYSTEM_WINDOW+17;
public static final int TYPE_POINTER = FIRST_SYSTEM_WINDOW+18;
public static final int TYPE_NAVIGATION_BAR = FIRST_SYSTEM_WINDOW+19;
public static final int TYPE_VOLUME_OVERLAY = FIRST_SYSTEM_WINDOW+20;
public static final int TYPE_BOOT_PROGRESS = FIRST_SYSTEM_WINDOW+21;
public static final int TYPE_INPUT_CONSUMER = FIRST_SYSTEM_WINDOW+22;
public static final int TYPE_DREAM = FIRST_SYSTEM_WINDOW+23;
public static final int TYPE_NAVIGATION_BAR_PANEL = FIRST_SYSTEM_WINDOW+24;
public static final int TYPE_DISPLAY_OVERLAY = FIRST_SYSTEM_WINDOW+26;
public static final int TYPE_MAGNIFICATION_OVERLAY = FIRST_SYSTEM_WINDOW+27;
public static final int TYPE_PRIVATE_PRESENTATION = FIRST_SYSTEM_WINDOW+30;
public static final int TYPE_VOICE_INTERACTION = FIRST_SYSTEM_WINDOW+31;
public static final int TYPE_ACCESSIBILITY_OVERLAY = FIRST_SYSTEM_WINDOW+32;
public static final int TYPE_VOICE_INTERACTION_STARTING = FIRST_SYSTEM_WINDOW+33;
public static final int TYPE_DOCK_DIVIDER = FIRST_SYSTEM_WINDOW+34;
public static final int TYPE_QS_DIALOG = FIRST_SYSTEM_WINDOW+35;
public static final int TYPE_SCREENSHOT = FIRST_SYSTEM_WINDOW + 36;
public static final int TYPE_PRESENTATION = FIRST_SYSTEM_WINDOW + 37;
public static final int TYPE_APPLICATION_OVERLAY = FIRST_SYSTEM_WINDOW + 38;
public static final int LAST_SYSTEM_WINDOW = 2999;
Window都有自己的Layer，即z-order，表示在屏幕上顯示的層級順序。Application Window都屬於Application Layer，值爲2，其它的則不同，它們在WindowManagerPolicy可以找到，代碼如下。
int APPLICATION_LAYER = 2;
int APPLICATION_MEDIA_SUBLAYER = -2;
int APPLICATION_MEDIA_OVERLAY_SUBLAYER = -1;
int APPLICATION_PANEL_SUBLAYER = 1;
int APPLICATION_SUB_PANEL_SUBLAYER = 2;
int APPLICATION_ABOVE_SUB_PANEL_SUBLAYER = 3;
default int getWindowLayerFromTypeLw(int type, boolean canAddInternalSystemWindow) {
if (type >= FIRST_APPLICATION_WINDOW && type <= LAST_APPLICATION_WINDOW) {
return APPLICATION_LAYER;
}
switch (type) {
case TYPE_WALLPAPER:
// wallpaper is at the bottom, though the window manager may move it.
return 1;
case TYPE_PRESENTATION:
case TYPE_PRIVATE_PRESENTATION:
return APPLICATION_LAYER;
case TYPE_DOCK_DIVIDER:
return APPLICATION_LAYER;
case TYPE_QS_DIALOG:
return APPLICATION_LAYER;
case TYPE_PHONE:
return 3;
case TYPE_SEARCH_BAR:
case TYPE_VOICE_INTERACTION_STARTING:
return 4;
case TYPE_VOICE_INTERACTION:
// voice interaction layer is almost immediately above apps.
return 5;
case TYPE_INPUT_CONSUMER:
return 6;
case TYPE_SYSTEM_DIALOG:
return 7;
case TYPE_TOAST:
// toasts and the plugged-in battery thing
return 8;
case TYPE_PRIORITY_PHONE:
// SIM errors and unlock. Not sure if this really should be in a high layer.
return 9;
case TYPE_SYSTEM_ALERT:
// like the ANR / app crashed dialogs
return canAddInternalSystemWindow ? 11 : 10;
case TYPE_APPLICATION_OVERLAY:
return 12;
case TYPE_DREAM:
// used for Dreams (screensavers with TYPE_DREAM windows)
return 13;
case TYPE_INPUT_METHOD:
// on-screen keyboards and other such input method user interfaces go here.
return 14;
case TYPE_INPUT_METHOD_DIALOG:
// on-screen keyboards and other such input method user interfaces go here.
return 15;
case TYPE_STATUS_BAR_SUB_PANEL:
return 17;
case TYPE_STATUS_BAR:
return 18;
case TYPE_STATUS_BAR_PANEL:
return 19;
case TYPE_KEYGUARD_DIALOG:
return 20;
case TYPE_VOLUME_OVERLAY:
// the on-screen volume indicator and controller shown when the user
// changes the device volume
return 21;
case TYPE_SYSTEM_OVERLAY:
// the on-screen volume indicator and controller shown when the user
// changes the device volume
return canAddInternalSystemWindow ? 22 : 11;
case TYPE_NAVIGATION_BAR:
// the navigation bar, if available, shows atop most things
return 23;
case TYPE_NAVIGATION_BAR_PANEL:
// some panels (e.g. search) need to show on top of the navigation bar
return 24;
case TYPE_SCREENSHOT:
// screenshot selection layer shouldn't go above system error, but it should cover
// navigation bars at the very least.
return 25;
case TYPE_SYSTEM_ERROR:
// system-level error dialogs
return canAddInternalSystemWindow ? 26 : 10;
case TYPE_MAGNIFICATION_OVERLAY:
// used to highlight the magnified portion of a display
return 27;
case TYPE_DISPLAY_OVERLAY:
// used to simulate secondary display devices
return 28;
case TYPE_DRAG:
// the drag layer: input for drag-and-drop is associated with this window,
// which sits above all other focusable windows
return 29;
case TYPE_ACCESSIBILITY_OVERLAY:
// overlay put by accessibility services to intercept user interaction
return 30;
case TYPE_SECURE_SYSTEM_OVERLAY:
return 31;
case TYPE_BOOT_PROGRESS:
return 32;
case TYPE_POINTER:
// the (mouse) pointer layer
return 33;
default:
Slog.e("WindowManager", "Unknown window type: " + type);
return APPLICATION_LAYER;
}
}
default int getSubWindowLayerFromTypeLw(int type) {
switch (type) {
case TYPE_APPLICATION_PANEL:
case TYPE_APPLICATION_ATTACHED_DIALOG:
return APPLICATION_PANEL_SUBLAYER;
case TYPE_APPLICATION_MEDIA:
return APPLICATION_MEDIA_SUBLAYER;
case TYPE_APPLICATION_MEDIA_OVERLAY:
return APPLICATION_MEDIA_OVERLAY_SUBLAYER;
case TYPE_APPLICATION_SUB_PANEL:
return APPLICATION_SUB_PANEL_SUBLAYER;
case TYPE_APPLICATION_ABOVE_SUB_PANEL:
return APPLICATION_ABOVE_SUB_PANEL_SUBLAYER;
}
Slog.e("WindowManager", "Unknown sub-window type: " + type);
return 0;
}
Window的Layer，上面只是從1開始逐個遞增1，在轉換爲z-order時，還要進行轉換，首先乘10000，然後偏移1000，同類的Window逐個遞增5，這些值在WindowManagerService中定義，代碼如下所示。
/** How much to multiply the policy's type layer, to reserve room
* for multiple windows of the same type and Z-ordering adjustment
* with TYPE_LAYER_OFFSET. */
static final int TYPE_LAYER_MULTIPLIER = 10000;
/** Offset from TYPE_LAYER_MULTIPLIER for moving a group of windows above
* or below others in the same layer. */
static final int TYPE_LAYER_OFFSET = 1000;
/** How much to increment the layer for each window, to reserve room
* for effect surfaces between them.
*/
static final int WINDOW_LAYER_MULTIPLIER = 5;
Java層與Native層的Layer設置是通過SurfaceControl的setLayer完成的，在Native層由SurfaceComposer進行合成。
5、WindowState
WindowState是Android中的事實Window，WindowManager真正管理的是WindowState而不是Window。WindowState在WindowManagerService中創建，從上面的addView的時序圖中可以看出。創建WindowState之後，還需要設置上文提到的Window Layer，通過InputChannel與IMS取得聯繫，將Session中維護的Window個數加1，最後通過WindowToken將這個WindowState添加到WindowContainer中。
6、WindowToken
WindowToken是個容器，將相關的WindowState收集到一起，同樣是在WindowManagerService中創建。真正的token是IBinder類型的成員變量token，用於IPC。WindowToken有個子類AppWindowToken，用於Application和Activity。
7、Session
Session是個客戶端對象，每個進程只有一個，與WindowManagerService進行交互。Session對應的interface爲IWindowSession，在WindowManagerGlobal中實例化。
8、Surface
View或Window真正地是在一個Surface上進行描畫的，Surface即一個Buffer，由輔助類SurfaceControl進行控制，上文提到的Window Layer的設置就是由SurfaceControl與Native層進行交互的。