mEditText = ((EditText) findViewById(R.id.editText));
    //创建PerformEdit，一定要传入不为空的EditText
    mPerformEdit = new PerformEdit(mEditText);
    mPerformEdit.setDefaultText("这是初始值,不做撤销记录");

 //撤销
 mPerformEdit.undo();
    //重做
    mPerformEdit.redo();
    //清除历史
    mPerformEdit.clearHistory();