管理Activity的实例

Android能够展现给用户的界面都是继承来自Activity,虽然Android操作系统能根据当前Activity的状态通过维护一个栈来进行管理，但是

开发人员只能在每个activity的所在的state改变的事件中进行相关的操作。而且，如果一个activity想去获得某个activity的时候，也是比较

麻烦的。还有，比如我想给当前如果是Home的界面，需要校验是否需要显示登录窗口，那如何去处理将不会让校验代码出现在Home的Activity中。因为本身显示登录窗口与否和当前的Activity没多大关系。下面就给出一些项目中的真实案例的代码，供大家去看看。

 

ActivityManager.这个类除了模拟栈的行为，还添加一些额外的功能。比如用户是否身份有效。

public class ActivityManager {private ActivityManager() {}private static ActivityManager instance = new ActivityManager();public static ActivityManager getInstance() {return instance;}private List<Activity> activities = new ArrayList<Activity>();private Activity topActivity;private boolean topAcitivityActivited;private boolean waitingForDialogContainer = true;private boolean logining = false;private String loginPrompt;public void addActivity(Activity activity) {if (!activities.contains(activity)) {activities.add(activity);}}public void removeActivity(Activity activity) {activities.remove(activity);}public void setTopActivity(Activity topActivity) {this.topActivity = topActivity;}public Activity getTopActivity() {return topActivity;}public void setTopAcitivityActivited(boolean topAcitivityActivited) {this.topAcitivityActivited = topAcitivityActivited;if (waitingForDialogContainer) {waitingForDialogContainer = false;new Handler().post(new Runnable() {public void run() {showLoginDialog(loginPrompt);}});}}public boolean isTopAcitivityActivited() {return topAcitivityActivited;}public void showLoginDialog(String initialMessage) {if (logining) {return;}if (topActivity != null && topAcitivityActivited == true) {logining = true;new LoginView(topActivity, initialMessage).show();} else {waitingForDialogContainer = true;loginPrompt = initialMessage;}}@SuppressWarnings("unchecked")public <T extends Activity> T getActivity(Class<T> cls){for(Activity act : activities){if(act.getClass() == cls){return (T)act;}}return null;}private void quit() {for (Activity activity : activities) {activity.finish();}waitingForDialogContainer = true;loginPrompt = null;}public void onLoginReturned(boolean result) {logining = false;if (!result) {quit();}}}

 

ManagedActivity:这个类继承来自Activity.为了方便让ActivityManager的管理，每个Activity都继承来自该类。代码如下。

public class ManagedActivity extends Activity{@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);ActivityManager.getInstance().addActivity(this);}@Overrideprotected void onPause() {super.onPause();ActivityManager.getInstance().setTopAcitivityActivited(false);}@Overrideprotected void onDestroy() {super.onDestroy();ActivityManager.getInstance().removeActivity(this);}@Overrideprotected void onStart() {super.onStart();ActivityManager.getInstance().setTopActivity(this);ActivityManager.getInstance().setTopAcitivityActivited(true);}}

 

ActivityManager的showLoginDialog可用来根据登录窗台来检测是否当前需要弹出登录框。而且这只是一部分小的作用，更多的大家

可以想想，这个ActivityManager中还可以处理很多你想处理的功能，当那些界面状态发生变化。