public class ScreenManager {
 private static Stack<Activity> activityStack;
 private static ScreenManager instance;
 private ScreenManager(){
 }
 public static ScreenManager getScreenManager(){
 if(instance==null){
  instance=new ScreenManager();
 }
 return instance;
 }
//退出栈顶Activity
 public void popActivity(Activity activity){
 if(activity!=null){
  activity.finish();
  activityStack.remove(activity);
  activity=null;
 }
 }

//获得当前栈顶Activity
 public Activity currentActivity(){
 Activity activity=activityStack.lastElement();
 return activity;
 }

//将当前Activity推入栈中
 public void pushActivity(Activity activity){
 if(activityStack==null){
  activityStack=new Stack<Activity>();
 }
 activityStack.add(activity);
 }
 //退出栈中所有Activity
 public void popAllActivityExceptOne(Class cls){
 while(true){
  Activity activity=currentActivity();
  if(activity==null){
  break;
  }
  if(activity.getClass().equals(cls) ){
  break;
  }
  popActivity(activity);
 }
 }
}