Android和設計模式：代理模式

 

    最近在繼續iPhone業務的同時還需要重新拾起Android。在有些生疏的情況下，決定從Android源碼中感悟一些Android的風格和方式。在學習源碼的過程中也發現了一些通用的模式，希望通過一個系列的文章總結和分享下。

    代理模式爲其他對象提供一種代理以控制對這個對象的訪問。代理還分成遠程代理、虛代理、保護代理和智能指針等。Android系統中利用AIDL定義一種遠程服務時就需要用到代理模式。以StatusBarManager爲例，其代理模式的類圖如下：

主要的實現代碼如下：

public class StatusBarManager {
    ......
    private Context mContext;
    private IStatusBarService mService;
    private IBinder mToken = new Binder();

    StatusBarManager(Context context) {
        mContext = context;
        mService = IStatusBarService.Stub.asInterface(
                ServiceManager.getService(Context.STATUS_BAR_SERVICE));
    }

    public void disable(int what) {
        try {
            mService.disable(what, mToken, mContext.getPackageName());
        } catch (RemoteException ex) {
            // system process is dead anyway.
            throw new RuntimeException(ex);
        }
    }
    public void expand() {
        try {
            mService.expand();
        } catch (RemoteException ex) {
            // system process is dead anyway.
            throw new RuntimeException(ex);
        }
    }
    public void collapse() {
        try {
            mService.collapse();
        } catch (RemoteException ex) {
            // system process is dead anyway.
            throw new RuntimeException(ex);
        }
    }

    public void setIcon(String slot, int iconId, int iconLevel) {
        try {
            mService.setIcon(slot, mContext.getPackageName(), iconId, iconLevel);
        } catch (RemoteException ex) {
            // system process is dead anyway.
            throw new RuntimeException(ex);
        }
    }

    public void removeIcon(String slot) {
        try {
            mService.removeIcon(slot);
        } catch (RemoteException ex) {
            // system process is dead anyway.
            throw new RuntimeException(ex);
        }
    }

    public void setIconVisibility(String slot, boolean visible) {
        try {
            mService.setIconVisibility(slot, visible);
        } catch (RemoteException ex) {
            // system process is dead anyway.
            throw new RuntimeException(ex);
        }
    }
}
    其中作爲代理的StatusBarManager通過 IStatusBarService.Stub.asInterface(ServiceManager.getService(Context.STATUS_BAR_SERVICE))獲取到了遠程服務，用戶通過StatusBarManager同真正的服務交互。