Create Framework 设计模式.md

blogs/Android/Framework/Interview/综合性面试题/Framework 设计模式.md

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+---
+Framework 用到了哪些设计模式？
+---
+
+1. 是否熟悉常用的设计模式
+2. 是否对 Framework 源码有所了解
+3. 是否善于学习和总结
+
+#### 单例模式
+
+```java
+private static final Singleton<IActivityManager> gDefault = new Singleton<IActivityManager>(){
+    protected IActivityManager create(){
+        IBinder b = ServiceManager.getService("activity");
+        IActivityManager am = asInterface(b);
+        return am;
+    }
+}
+static public IActivityManager getDefault(){
+    return gDefault.get();
+}
+```
+
+```java
+// 线程间单例
+private static final ThreadLocal<Choreographer> sThreadInstance = new ThreadLocal<Choreographer>(){
+    @Override
+    protected Choreographer initialValue(){
+        Looper looper = Looper.myLooper();
+        return new Choreographer(looper);
+    }
+}
+public static Choreographer getInstance(){
+    return sThreadInstance.get();
+}
+```
+
+```c++
+// 进程间单例
+// 单例：ServiceManager 中间人：Binder 驱动
+int main(int argc, char **argv){
+	struct binder_state *bs;
+    bs = binder_open(128*1024);
+    binder_become_context_manager(bs);
+}
+private static IServiceManager getIServiceManager(){
+    if(sServiceManager != null){
+        return sServiceManager;
+    }
+    sServiceManager = ServiceManagerNative.asInterface(BinderInternal.getContextObject());
+    return sServiceManager;
+}
+sp<IBinder> ProcessState::getContextObject(const sp<IBinder>&){
+    return getStrongProxyForHandle(0);
+}
+```
+
+#### 观察者模式
+
+```java
+public class ContentObservable extends Observable<ContextObserver>{
+	@OVerride
+	public void registerObserver(ContentObserver observer){
+		super.registerObserver(observer)l
+	}
+	public void notifyChange(boolean selfChange){
+		synchronized(mObservers){
+            for(ContentObserver observer: mObservers){
+                observer.onChange(selfChange, null);
+            }
+        }
+	}
+}
+void registerContentObserver(..., ContentObserver obsserver, ...){
+    getContentService().registerContentObserver(..., observer.getContentObserver(), ...);
+}
+public IContentOnserver getContentObserver(){
+    synchronized(mLock){
+        if(mTransport == null){
+            mTransport = new Transport(this);
+        }
+        return mTransport;
+    }
+}
+private static final class Transport extends IContentObserver.Stub{
+    private ContentObserver mContentObserver;
+    public Transport(ContentObserver contentObserver){
+        mContentObserver = contentObserver;
+    }
+    @Override
+    public void onChange(boolean selfChange, Uri uri, int userId){
+        ContentObserver contentObserver = mContentObserver;
+        if(contentObserver!=null){
+            contentObserver.dispatchChange(selfChange, uri, userId);
+        }
+    }
+}
+```
+
+#### 代理模式
+
+静态代理：
+
+```java
+class ActivityManagerProxy implements IActivityManager{
+	private IBinder mRemote;
+    public ActivityManagerProxy(IBinder remote){
+        mRemote. = remote;
+    }
+}
+class ActivityManagerNative extends Binder implements IActivityManager{
+    static public IActivityManager asInterface(IBinder obj){
+        if(obj == null){
+            return null;
+        }
+        IActivityManager in = (IActivityManager)obj.queryLocalInterface(descriptor);
+        if(in != null){
+            return in;
+        }
+        return new ActivityManagerProxy(obj);
+    }
+}
+
+int startActivity(IApplicationThread caller, ...) throws RemoteException{
+    Parcel data = Parcel.obtain();
+    Parcel reply = Parcel.obtain();
+    
+    mRemote.transact(START_ACTIVITY_TRANSACTION, data, reply, 0);
+}
+```
+
+动态代理：
+
+```java
+public class Decorator<T> implements InvocationHandler{
+    private final T mObject;
+    private final DecoratorListener mListener;
+    
+    public static <T> T newInstance(T obj, DecoratorListener listener){
+        return (T)Proxy.newProxyInstance(obj.getClass().getClassLoader(),
+                                        obj.getClass().getInterfaces(),new Decorator<T>(obj, listener));
+    }
+    
+    private Decorator(T obj, DecoratorListener listener){
+        this.mObject = obj;
+        this.mListener = listener;
+    }
+}
+```
+