UITextField的协议方法

//将要开始输入时调用
-(BOOL)textFieldShouldBeginEditing:(UITextField *)textField
{
    return YES;
}
//将要输入结束时调用
-(BOOL)textFieldShouldEndEditing:(UITextField *)textField
{
    return YES;
}
//点击清除文字按钮时调用的事件
-(BOOL)textFieldShouldClear:(UITextField *)textField
{
    return YES;
}
//键盘上的return健
-(BOOL)textFieldShouldReturn:(UITextField *)textField
{
    return YES;
}