在Android中使用 ”堆栈法“来完全退出应用程序

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在Android开发中，有时候会遇到我们需要退出应用程序的时候，对于退出问题，众说纷云，有很多方法，至今本人没有发现较好的方法来解决这个问题：

1. 什么是”堆栈法“？

2. 什么时候适用”堆栈法“？

当app不支持横竖屏切换的时候，这时候用”堆栈法“来退出应用程序是最好的选择。如果你的app支持横竖屏切换，你需要保证你的Activity不被destroy()，否则就会直接退出，返回到桌面了。

3. 如何实现退出app的功能

step1. 把ScreenManager.java加到你的项目util工具包下，源代码如下：

/**
* This is a class used to exit from application. (poup all activities from stack)
*
*/
public class ScreenManager {

   private static Stack<BaseActivity> activityStack;
   private static ScreenManager instance;

   private ScreenManager() {
   }

   public static ScreenManager getScreenManager() {
       if (instance == null) {
           instance = new ScreenManager();
       }
       if (activityStack == null) {
           activityStack = new Stack<BaseActivity>();
       }
       return instance;
   }

   public void popActivity() {
       BaseActivity activity = activityStack.lastElement();
       if (activity != null) {
           activity.finish();
           activity = null;
       }
   }

   public void popActivity(BaseActivity activity) {
       if (activity != null) {
           activity.finish();
           activityStack.remove(activity);
           activity = null;
       }
   }

   public BaseActivity currentActivity() {
       try {
           BaseActivity activity = activityStack.lastElement();
           return activity;
       } catch (Exception e) {
           return null;
       }

   }

   public void pushActivity(BaseActivity activity) {

       activityStack.add(activity);
   }

   public void popAllActivityExceptOne(Class<?> cls) {
       while (true) {
           BaseActivity activity = currentActivity();
           if (activity == null) {
               break;
           }
           if (activity.getClass().equals(cls)) {
               break;
           }
           popActivity(activity);
       }
   }

   public void popAllActivityAddMe(BaseActivity activity) {
       while (true) {
           BaseActivity a = currentActivity();
           if (a == null) {
               break;
           }
           if(!activity.equals(a))
               popActivity(a);
           else
               activityStack.remove(activity);
       }
       pushActivity(activity);

   }

   public void popAllActivity() {
       activityStack.removeAllElements();
       activityStack.clear();
   }

}

step2. 让所有yourActivity 继承 BaseActivity.java, BaseActivity.java的代码如下：

public class BaseActivity extends Activity {

   @Override
   protected void onCreate(Bundle savedInstanceState) {
       // TODO Auto-generated method stub
       super.onCreate(savedInstanceState);
       ScreenManager.getScreenManager().popAllActivityAddMe(this);
   }

｝

step3. 设置用户操作接口，用来退出。如在登录页面当用户按back键时，这时候调用退出app功能。

在LoginActivity中添加：

@Override
   public boolean onKeyDown(int keyCode, KeyEvent event) {
       // TODO Auto-generated method stub
       if (keyCode == KeyEvent.KEYCODE_BACK) {
           // skill LoginActivity or close the application
           new AlertDialog.Builder(this).setTitle("").setIcon(R.drawable.icon).setMessage(
           R.string.exit).setNegativeButton(
                   R.string.str_no, new DialogInterface.OnClickListener() {
                       @Override
                       public void onClick(DialogInterface dialog, int which) {
                       }
                   }).setPositiveButton(R.string.str_yes,
                           new DialogInterface.OnClickListener() {
                       public void onClick(final DialogInterface dialog,
                               int whichButton) {

                           dialog.dismiss();

                           ScreenManager.getScreenManager().popAllActivity();
                           android.os.Process.killProcess(android.os.Process.myPid());
                           finish();
                           System.exit(0);
                       }
                   }).show();
           return false;
       }
       return super.onKeyDown(keyCode, event);
   }

这样就可以完全退出app了，且此法通用于各个sdk version