从一个Activity中要通过intent调出另一个Activity的话，需要使用 FLAG_ACTIVITY_NEW_TASK 
否则的话，会有force close： 
03-01 18:49:37.888 E/AndroidRuntime( 2706): FATAL EXCEPTION: main 
03-01 18:49:37.888 E/AndroidRuntime( 2706): android.util.AndroidRuntimeException: Calling startActivity() from outside of an Activity  context requires the FLAG_ACTIVITY_NEW_TASK flag. Is this really what you want? 

FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS: 

如果调出的Activtivity只是一个功能片段，并没有实际的意义，也没有必要出现在长按Home键调出最近使用过的程序类表中，那么使用FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS 

Intent intent = new Intent(this, WaitingFallBackDialog.class); 
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK | Intent.FLAG_ACTIVITY_EXCLUDE_FROM_RECENTS); 
startActivity(intent); 

Calling startActivity() from outside of an Activity context requires the FLAG_ACTIVITY_NEW_TASK fla