// 清除按钮左移一个单元
- (CGRect)clearButtonRectForBounds:(CGRect)bounds
{
    CGRect rect = [super clearButtonRectForBounds:bounds];
    if (_isReservedRightView){
        rect = CGRectOffset(rect, -rect.size.width, 0);
    }
    return rect;
}
 
// 控制 placeHolder 的位置，左右缩 8
- (CGRect)textRectForBounds:(CGRect)bounds
{
    CGRect rect = [super textRectForBounds:bounds];
    return CGRectInset(rect, 8, 0);
}
 
// 控制文本的位置，左右缩 8
- (CGRect)editingRectForBounds:(CGRect)bounds
{
    CGRect rect = [super textRectForBounds:bounds];
    return CGRectInset(rect, 8, 0);
}
 
// 重写方法，固定viewMode为Always
- (void)setLeftView:(UIView *)leftView
{
    [super setLeftView:leftView];
    self.leftViewMode = UITextFieldViewModeAlways;
}