你可以试试这个：

    UIImageView *envelopeView = [[UIImageView alloc] initWithFrame:CGRectMake(20, 0, 30, 30)];
    envelopeView.image = [UIImage imageNamed:@"comment-128.png"];
    envelopeView.contentMode = UIViewContentModeScaleAspectFit;
  UIView *test=  [[UIView alloc]initWithFrame:CGRectMake(20, 0, 30, 30)];
    [test addSubview:envelopeView];
    [self.textField.leftView setFrame:envelopeView.frame];
    self.textField.leftView =test;
        self.textField.leftViewMode = UITextFieldViewModeAlways;