桥接模式（Bridge Pattern）定义和使用场景
- 定义
桥接模式(Bridge Pattern)：将抽象部分与它的实现部分分离，使它们都可以独立地变化。它是一种对象结构型模式，又称为柄体(Handle and Body)模式或接口(Interface)模式。
实现系统可能有多个角度分类，每一种角度都可能变化，那么把这种多角度分类给分离出来让他们独立变化，减少他们之间耦合。
- 使用场景
如果一个系统需要在构件的抽象化和具体角色之间增加更多的灵活性，避免在两个层次之间建立静态的继承联系，可以通过桥接模式使它们在抽象层建立一个关联关系。对于那些不希望使用继承或因为多层次继承导致系统类的个数急剧增加的系统，桥接模式尤为适用。一个类存在两个独立变化的维度，且这两个维度都需要进行扩展。 -
桥接模式的UML类图
桥接模式
Abstraction：抽象部分。该类保持一个对实现部分的引用，抽象部分中的方法需要调用实现部分的对象来实现，该类一般为抽象类。
RefinedAbstraction：优化的抽象部分。抽象部分的具体实现，该类一般是对抽象部分的方法进行完善和扩展。
Implementor：实现部分。可以为接口或者抽象类，其方法不一定要与抽象部分中的一致，一般情况下是由实现部分提供基本的操作，而抽象部分定义的则是基于实现部分这些基本操作的业务方法。
ConcreteImplementorA/ConcreteImplementorB：实现部分的具体实现。完善实现部分中方法定义的具体逻辑。
Client：客户类，客户端程序。 - 生活实例阐述
- 开关与具体的电器，开关的类型有很多，也是有各种各样的，这两者是独立的且又有耦合。
- 电脑的主机箱和电脑厂商，主机箱的样式是有多种多样的而电脑的厂商也是有很多，所以这也可以是一种桥接模式。
3.Java语言通过Java虚拟机实现了平台的无关性，Java语言的程序和运行Java成语的平台的，这也是桥接模式的一种实现。
桥接模式的简单代码实例
用不同颜色的笔画出不同形状的图形，画笔的颜色可以是有多种多样的，画的图形也可以是有正方形、长方形等不同的图形。
public interface Paint {
void userPaintColor();
}
public class RedPaint implements Paint{
@Override
public void userPaintColor() {
System.out.println("用红色的笔去画");
}
}
public class BluePaint implements Paint{
@Override
public void userPaintColor() {
System.out.println("用蓝色的笔去画");
}
}
public abstract class DrawShape {
protected Paint paintImple;
public DrawShape(Paint paintImple){
this.paintImple=paintImple;
}
public abstract void drawShape();
}
public class CircleShape extends DrawShape{
public CircleShape(Paint paintImple) {
super(paintImple);
}
@Override
public void drawShape() {
paintImple.userPaintColor();
System.out.println("画出圆形");
}
}
public class SquareShape extends DrawShape{
public SquareShape(Paint paintImple) {
super(paintImple);
}
@Override
public void drawShape() {
paintImple.userPaintColor();
System.out.println("画出正方形");
}
}
public class TestDemo {
public static void main(String a[])
{
CircleShape circleShape=new CircleShape(new RedPaint());
circleShape.drawShape();
SquareShape squareShape=new SquareShape(new RedPaint());
squareShape.drawShape();
}
}
打印结果
image.png
Android源码中的桥接模式实现
在View的视图层中，CheckBox、CompoundButton、Button、TextView和View之间构成一个继承关系的视图层级，每一层级都仅仅是对一个类型控件的描述，定义了该类控件所拥有的基本属性和行为，但是将它们真正绘制到屏幕的部分是由与View相关的功能实现类DisplayList、HardwareLayer和Canvas负责。
-
另外一个比较典型Window与WindowManager之间的关系，Window和PhoneWindow构成窗口的抽象部分，其中Window类为该抽象部分的抽象接口，PhoneWindow为抽象部分具体的实现及扩展。WindowsManager则为实现部分的基类，WindowManagerImpl为实现部分具体的实现及扩展，其使用WindowManagerGlobal通过IWindowManager接口与WindowManagerService进行交互，并由WMS完成具体的窗口管理工具。
image1.png
WindowManagerServer
在Android的framework层主要就是由WindowManagerServer与另外一个系统服务ActivityManagerService还有View所构成。
WindowManagerService在SystemServer中的main方法中启动
public static void main(String[] args) {
new SystemServer().run();
}
public SystemServer() {
// Check for factory test mode.
mFactoryTestMode = FactoryTest.getMode();
}
private void run() {
try {
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "InitBeforeStartServices");
// If a device's clock is before 1970 (before 0), a lot of
// APIs crash dealing with negative numbers, notably
// java.io.File#setLastModified, so instead we fake it and
// hope that time from cell towers or NTP fixes it shortly.
if (System.currentTimeMillis() < EARLIEST_SUPPORTED_TIME) {
Slog.w(TAG, "System clock is before 1970; setting to 1970.");
SystemClock.setCurrentTimeMillis(EARLIEST_SUPPORTED_TIME);
}
// If the system has "persist.sys.language" and friends set, replace them with
// "persist.sys.locale". Note that the default locale at this point is calculated
// using the "-Duser.locale" command line flag. That flag is usually populated by
// AndroidRuntime using the same set of system properties, but only the system_server
// and system apps are allowed to set them.
//
// NOTE: Most changes made here will need an equivalent change to
// core/jni/AndroidRuntime.cpp
if (!SystemProperties.get("persist.sys.language").isEmpty()) {
final String languageTag = Locale.getDefault().toLanguageTag();
SystemProperties.set("persist.sys.locale", languageTag);
SystemProperties.set("persist.sys.language", "");
SystemProperties.set("persist.sys.country", "");
SystemProperties.set("persist.sys.localevar", "");
}
// Here we go!
Slog.i(TAG, "Entered the Android system server!");
EventLog.writeEvent(EventLogTags.BOOT_PROGRESS_SYSTEM_RUN, SystemClock.uptimeMillis());
// In case the runtime switched since last boot (such as when
// the old runtime was removed in an OTA), set the system
// property so that it is in sync. We can't do this in
// libnativehelper's JniInvocation::Init code where we already
// had to fallback to a different runtime because it is
// running as root and we need to be the system user to set
// the property. http://b/11463182
SystemProperties.set("persist.sys.dalvik.vm.lib.2", VMRuntime.getRuntime().vmLibrary());
// Enable the sampling profiler.
if (SamplingProfilerIntegration.isEnabled()) {
SamplingProfilerIntegration.start();
mProfilerSnapshotTimer = new Timer();
mProfilerSnapshotTimer.schedule(new TimerTask() {
@Override
public void run() {
SamplingProfilerIntegration.writeSnapshot("system_server", null);
}
}, SNAPSHOT_INTERVAL, SNAPSHOT_INTERVAL);
}
// Mmmmmm... more memory!
VMRuntime.getRuntime().clearGrowthLimit();
// The system server has to run all of the time, so it needs to be
// as efficient as possible with its memory usage.
VMRuntime.getRuntime().setTargetHeapUtilization(0.8f);
// Some devices rely on runtime fingerprint generation, so make sure
// we've defined it before booting further.
Build.ensureFingerprintProperty();
// Within the system server, it is an error to access Environment paths without
// explicitly specifying a user.
Environment.setUserRequired(true);
// Within the system server, any incoming Bundles should be defused
// to avoid throwing BadParcelableException.
BaseBundle.setShouldDefuse(true);
// Ensure binder calls into the system always run at foreground priority.
BinderInternal.disableBackgroundScheduling(true);
// Increase the number of binder threads in system_server
BinderInternal.setMaxThreads(sMaxBinderThreads);
// Prepare the main looper thread (this thread).
android.os.Process.setThreadPriority(
android.os.Process.THREAD_PRIORITY_FOREGROUND);
android.os.Process.setCanSelfBackground(false);
Looper.prepareMainLooper();
// Initialize native services.
System.loadLibrary("android_servers");
// Check whether we failed to shut down last time we tried.
// This call may not return.
performPendingShutdown();
// Initialize the system context.
createSystemContext();
// Create the system service manager.
mSystemServiceManager = new SystemServiceManager(mSystemContext);
LocalServices.addService(SystemServiceManager.class, mSystemServiceManager);
} finally {
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
}
// Start services.
try {
Trace.traceBegin(Trace.TRACE_TAG_SYSTEM_SERVER, "StartServices");
// 安装应用需要的
startBootstrapServices();
startCoreServices();
// 启动服务
startOtherServices();
} catch (Throwable ex) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting system services", ex);
throw ex;
} finally {
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
}
// For debug builds, log event loop stalls to dropbox for analysis.
if (StrictMode.conditionallyEnableDebugLogging()) {
Slog.i(TAG, "Enabled StrictMode for system server main thread.");
}
// Loop forever.
Looper.loop();
throw new RuntimeException("Main thread loop unexpectedly exited");
}
private void startOtherServices() {
final Context context = mSystemContext;
VibratorService vibrator = null;
IMountService mountService = null;
NetworkManagementService networkManagement = null;
NetworkStatsService networkStats = null;
NetworkPolicyManagerService networkPolicy = null;
ConnectivityService connectivity = null;
NetworkScoreService networkScore = null;
NsdService serviceDiscovery= null;
WindowManagerService wm = null;
SerialService serial = null;
NetworkTimeUpdateService networkTimeUpdater = null;
CommonTimeManagementService commonTimeMgmtService = null;
InputManagerService inputManager = null;
TelephonyRegistry telephonyRegistry = null;
ConsumerIrService consumerIr = null;
MmsServiceBroker mmsService = null;
HardwarePropertiesManagerService hardwarePropertiesService = null;
boolean disableStorage = SystemProperties.getBoolean("config.disable_storage", false);
boolean disableBluetooth = SystemProperties.getBoolean("config.disable_bluetooth", false);
boolean disableLocation = SystemProperties.getBoolean("config.disable_location", false);
boolean disableSystemUI = SystemProperties.getBoolean("config.disable_systemui", false);
boolean disableNonCoreServices = SystemProperties.getBoolean("config.disable_noncore", false);
boolean disableNetwork = SystemProperties.getBoolean("config.disable_network", false);
boolean disableNetworkTime = SystemProperties.getBoolean("config.disable_networktime", false);
boolean disableRtt = SystemProperties.getBoolean("config.disable_rtt", false);
boolean disableMediaProjection = SystemProperties.getBoolean("config.disable_mediaproj",
false);
boolean disableSerial = SystemProperties.getBoolean("config.disable_serial", false);
boolean disableSearchManager = SystemProperties.getBoolean("config.disable_searchmanager",
false);
boolean disableTrustManager = SystemProperties.getBoolean("config.disable_trustmanager",
false);
boolean disableTextServices = SystemProperties.getBoolean("config.disable_textservices", false);
boolean disableSamplingProfiler = SystemProperties.getBoolean("config.disable_samplingprof",
false);
boolean isEmulator = SystemProperties.get("ro.kernel.qemu").equals("1");
try {
Slog.i(TAG, "Reading configuration...");
SystemConfig.getInstance();
traceBeginAndSlog("StartSchedulingPolicyService");
ServiceManager.addService("scheduling_policy", new SchedulingPolicyService());
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
mSystemServiceManager.startService(TelecomLoaderService.class);
traceBeginAndSlog("StartTelephonyRegistry");
telephonyRegistry = new TelephonyRegistry(context);
ServiceManager.addService("telephony.registry", telephonyRegistry);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("StartEntropyMixer");
mEntropyMixer = new EntropyMixer(context);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
mContentResolver = context.getContentResolver();
Slog.i(TAG, "Camera Service");
mSystemServiceManager.startService(CameraService.class);
// The AccountManager must come before the ContentService
traceBeginAndSlog("StartAccountManagerService");
mSystemServiceManager.startService(ACCOUNT_SERVICE_CLASS);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("StartContentService");
mSystemServiceManager.startService(CONTENT_SERVICE_CLASS);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("InstallSystemProviders");
mActivityManagerService.installSystemProviders();
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("StartVibratorService");
vibrator = new VibratorService(context);
ServiceManager.addService("vibrator", vibrator);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("StartConsumerIrService");
consumerIr = new ConsumerIrService(context);
ServiceManager.addService(Context.CONSUMER_IR_SERVICE, consumerIr);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("StartAlarmManagerService");
mSystemServiceManager.startService(AlarmManagerService.class);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("InitWatchdog");
final Watchdog watchdog = Watchdog.getInstance();
watchdog.init(context, mActivityManagerService);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("StartInputManagerService");
inputManager = new InputManagerService(context);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("StartWindowManagerService");
wm = WindowManagerService.main(context, inputManager,
mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,
!mFirstBoot, mOnlyCore);
ServiceManager.addService(Context.WINDOW_SERVICE, wm);
ServiceManager.addService(Context.INPUT_SERVICE, inputManager);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("StartVrManagerService");
mSystemServiceManager.startService(VrManagerService.class);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
mActivityManagerService.setWindowManager(wm);
inputManager.setWindowManagerCallbacks(wm.getInputMonitor());
inputManager.start();
// TODO: Use service dependencies instead.
mDisplayManagerService.windowManagerAndInputReady();
// Skip Bluetooth if we have an emulator kernel
// TODO: Use a more reliable check to see if this product should
// support Bluetooth - see bug 988521
if (isEmulator) {
Slog.i(TAG, "No Bluetooth Service (emulator)");
} else if (mFactoryTestMode == FactoryTest.FACTORY_TEST_LOW_LEVEL) {
Slog.i(TAG, "No Bluetooth Service (factory test)");
} else if (!context.getPackageManager().hasSystemFeature
(PackageManager.FEATURE_BLUETOOTH)) {
Slog.i(TAG, "No Bluetooth Service (Bluetooth Hardware Not Present)");
} else if (disableBluetooth) {
Slog.i(TAG, "Bluetooth Service disabled by config");
} else {
mSystemServiceManager.startService(BluetoothService.class);
}
traceBeginAndSlog("ConnectivityMetricsLoggerService");
mSystemServiceManager.startService(MetricsLoggerService.class);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("IpConnectivityMetrics");
mSystemServiceManager.startService(IpConnectivityMetrics.class);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
traceBeginAndSlog("PinnerService");
mSystemServiceManager.startService(PinnerService.class);
Trace.traceEnd(Trace.TRACE_TAG_SYSTEM_SERVER);
} catch (RuntimeException e) {
Slog.e("System", "******************************************");
Slog.e("System", "************ Failure starting core service", e);
}
.....
省略其他代码
通过这个方法获取WindowmanagerService的实例，并且把他加到ServiceMange里面，然后其他进程都可以通过ServiceManager查询获取到WindowsManagerService。
wm = WindowManagerService.main(context, inputManager,
mFactoryTestMode != FactoryTest.FACTORY_TEST_LOW_LEVEL,
!mFirstBoot, mOnlyCore);
ServiceManager.addService(Context.WINDOW_SERVICE, wm);
WindowsManagerService的mian方法
private WindowManagerService(Context context, InputManagerService inputManager,
boolean haveInputMethods, boolean showBootMsgs, boolean onlyCore) {
mContext = context;
mHaveInputMethods = haveInputMethods;
mAllowBootMessages = showBootMsgs;
mOnlyCore = onlyCore;
mLimitedAlphaCompositing = context.getResources().getBoolean(
com.android.internal.R.bool.config_sf_limitedAlpha);
mHasPermanentDpad = context.getResources().getBoolean(
com.android.internal.R.bool.config_hasPermanentDpad);
mInTouchMode = context.getResources().getBoolean(
com.android.internal.R.bool.config_defaultInTouchMode);
mDrawLockTimeoutMillis = context.getResources().getInteger(
com.android.internal.R.integer.config_drawLockTimeoutMillis);
mAllowAnimationsInLowPowerMode = context.getResources().getBoolean(
com.android.internal.R.bool.config_allowAnimationsInLowPowerMode);
mInputManager = inputManager; // Must be before createDisplayContentLocked.
mDisplayManagerInternal = LocalServices.getService(DisplayManagerInternal.class);
mDisplaySettings = new DisplaySettings();
mDisplaySettings.readSettingsLocked();
mWallpaperControllerLocked = new WallpaperController(this);
mWindowPlacerLocked = new WindowSurfacePlacer(this);
mLayersController = new WindowLayersController(this);
LocalServices.addService(WindowManagerPolicy.class, mPolicy);
mPointerEventDispatcher = new PointerEventDispatcher(mInputManager.monitorInput(TAG_WM));
mFxSession = new SurfaceSession();
mDisplayManager = (DisplayManager)context.getSystemService(Context.DISPLAY_SERVICE);
mDisplays = mDisplayManager.getDisplays();
for (Display display : mDisplays) {
createDisplayContentLocked(display);
}
mKeyguardDisableHandler = new KeyguardDisableHandler(mContext, mPolicy);
mPowerManager = (PowerManager)context.getSystemService(Context.POWER_SERVICE);
mPowerManagerInternal = LocalServices.getService(PowerManagerInternal.class);
mPowerManagerInternal.registerLowPowerModeObserver(
new PowerManagerInternal.LowPowerModeListener() {
@Override
public void onLowPowerModeChanged(boolean enabled) {
synchronized (mWindowMap) {
if (mAnimationsDisabled != enabled && !mAllowAnimationsInLowPowerMode) {
mAnimationsDisabled = enabled;
dispatchNewAnimatorScaleLocked(null);
}
}
}
});
mAnimationsDisabled = mPowerManagerInternal.getLowPowerModeEnabled();
mScreenFrozenLock = mPowerManager.newWakeLock(
PowerManager.PARTIAL_WAKE_LOCK, "SCREEN_FROZEN");
mScreenFrozenLock.setReferenceCounted(false);
mAppTransition = new AppTransition(context, this);
mAppTransition.registerListenerLocked(mActivityManagerAppTransitionNotifier);
mBoundsAnimationController =
new BoundsAnimationController(mAppTransition, UiThread.getHandler());
mActivityManager = ActivityManagerNative.getDefault();
mAmInternal = LocalServices.getService(ActivityManagerInternal.class);
mAppOps = (AppOpsManager)context.getSystemService(Context.APP_OPS_SERVICE);
AppOpsManager.OnOpChangedInternalListener opListener =
new AppOpsManager.OnOpChangedInternalListener() {
@Override public void onOpChanged(int op, String packageName) {
updateAppOpsState();
}
};
mAppOps.startWatchingMode(AppOpsManager.OP_SYSTEM_ALERT_WINDOW, null, opListener);
mAppOps.startWatchingMode(AppOpsManager.OP_TOAST_WINDOW, null, opListener);
// Get persisted window scale setting
mWindowAnimationScaleSetting = Settings.Global.getFloat(context.getContentResolver(),
Settings.Global.WINDOW_ANIMATION_SCALE, mWindowAnimationScaleSetting);
mTransitionAnimationScaleSetting = Settings.Global.getFloat(context.getContentResolver(),
Settings.Global.TRANSITION_ANIMATION_SCALE, mTransitionAnimationScaleSetting);
setAnimatorDurationScale(Settings.Global.getFloat(context.getContentResolver(),
Settings.Global.ANIMATOR_DURATION_SCALE, mAnimatorDurationScaleSetting));
// Track changes to DevicePolicyManager state so we can enable/disable keyguard.
IntentFilter filter = new IntentFilter();
filter.addAction(DevicePolicyManager.ACTION_DEVICE_POLICY_MANAGER_STATE_CHANGED);
mContext.registerReceiver(mBroadcastReceiver, filter);
mSettingsObserver = new SettingsObserver();
mHoldingScreenWakeLock = mPowerManager.newWakeLock(
PowerManager.SCREEN_BRIGHT_WAKE_LOCK | PowerManager.ON_AFTER_RELEASE, TAG_WM);
mHoldingScreenWakeLock.setReferenceCounted(false);
mAnimator = new WindowAnimator(this);
mAllowTheaterModeWakeFromLayout = context.getResources().getBoolean(
com.android.internal.R.bool.config_allowTheaterModeWakeFromWindowLayout);
LocalServices.addService(WindowManagerInternal.class, new LocalService());
initPolicy();
// Add ourself to the Watchdog monitors.
Watchdog.getInstance().addMonitor(this);
SurfaceControl.openTransaction();
try {
createWatermarkInTransaction();
} finally {
SurfaceControl.closeTransaction();
}
showEmulatorDisplayOverlayIfNeeded();
}
public static WindowManagerService main(final Context context,
final InputManagerService im,
final boolean haveInputMethods, final boolean showBootMsgs,
final boolean onlyCore) {
final WindowManagerService[] holder = new WindowManagerService[1];
DisplayThread.getHandler().runWithScissors(new Runnable() {
@Override
public void run() {
holder[0] = new WindowManagerService(context, im,
haveInputMethods, showBootMsgs, onlyCore);
}
}, 0);
return holder[0];
}
桥接模式的优点
- 桥接模式实现了抽象化与实现化的脱耦。他们两个互相独立，不会影响到对方。
- 对于两个独立变化的维度，使用桥接模式再适合不过了。
- 对于“具体的抽象类”所做的改变，是不会影响到客户。