Android设计模式系列(3)--SDK源码之单例模式

public final class InputMethodManager {
    static final Object mInstanceSync = new Object();//同步
    //内部全局唯一实例
    static InputMethodManager mInstance;
 
    //对外api
    static public InputMethodManager getInstance(Context context) {
        return getInstance(context.getMainLooper());
    }
     
    /**
     * 内部api，供上面的外部api调用
     * @hide 系统隐藏的api
     */
    static public InputMethodManager getInstance(Looper mainLooper) {
        synchronized (mInstanceSync) {
            if (mInstance != null) {
                return mInstance;
            }
            IBinder b = ServiceManager.getService(Context.INPUT_METHOD_SERVICE);
            IInputMethodManager service = IInputMethodManager.Stub.asInterface(b);
            mInstance = new InputMethodManager(service, mainLooper);
        }
        return mInstance;
    }
}

class ContextImpl extends Context{
    @Override
    public Object getSystemService(String name) {
        if (WINDOW_SERVICE.equals(name)) {
            //... ... 省略下面n个if，else if
        } else if (INPUT_METHOD_SERVICE.equals(name)) {
            //获取输入法管理者唯一实例
            return InputMethodManager.getInstance(this);
        }  else if (KEYGUARD_SERVICE.equals(name)) {
             //... ... 省略下面n个if，else if
        } else if (ACCESSIBILITY_SERVICE.equals(name)) {
            //又见单例，无处不在
            return AccessibilityManager.getInstance(this);
        } else if (LOCATION_SERVICE.equals(name)) {
            //... ... 省略下面n个if，else if
        }  else if (NFC_SERVICE.equals(name)) {
            return getNfcManager();
        }
        return null;
    }
}