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().

ProgressDialog使用