询问当前编辑框能否被编辑 YES 能 NO 不能
- (BOOL)textFieldShouldBeginEditing:(UITextField *)textField
{
return YES;
}


当编辑框开始编辑时触发(获得焦点后触发)
- (void)textFieldDidBeginEditing:(UITextField *)textField
{

}


询问当前输入框是否可以结束编辑(键盘是否可以收回)
- (BOOL)textFieldShouldEndEditing:(UITextField *)textField
{

return YES;
}


当前输入框结束编辑时触发(键盘收回后触发).
- (void)textFieldDidEndEditing:(UITextField *)textField
{

}


当输入框文字发生变化时就会触发. (只有通过键盘输入时文字改变,触发)
- (BOOL)textField:(UITextField *)textField shouldChangeCharactersInRange:(NSRange)range replacementString:(NSString *)string
{
return YES;
}

用来控制输入框的清除按钮是否具有清除功能. YES 有 NO 没有
- (BOOL)textFieldShouldClear:(UITextField *)textField
{

return YES;
}

当点击键盘右下角的return按钮时触发
- (BOOL)textFieldShouldReturn:(UITextField *)textField
{
[textField resignFirstResponder];

return YES;
}