ProgressDialog使用
重点参考
http://blog.csdn.net/caesardadi/article/details/11982721
http://blog.csdn.net/chenshijun0101/article/details/11147051
public void cancel ()
Since: API Level 1
Cancel the dialog. This is essentially the same as calling dismiss(), but it will also call your DialogInterface.OnCancelListener (if registered).
public void dismiss ()
Since: API Level 1
Dismiss this dialog, removing it from the screen. This method can be
invoked safely from any thread. Note that you should not override this
method to do cleanup when the dialog is dismissed, instead implement
that in onStop().