目的是实现例如以下的效果：

自己定义UITextField_ide

UITextField的leftView是自己定义的UIView，当中：

1、包括一个居中显示的icon。而且上，左，下各有1px的间隙

2、左上和左下是圆角，右边没有圆角

居中展示icon

关键是leftView不是UIImageView。而是把UIImageView设置为subview

CGFloat height = frame.size.height;
        
UIView *leftView = [[UIView alloc] initWithFrame:CGRectMake(0, 1, height - 1, height - 2)];
        
UIImageView *icon = [[UIImageView alloc] initWithImage:[UIImage imageNamed:iconName]];
icon.frame = CGRectMake(height / 4, height / 4, height / 2, height / 2);
[leftView addSubview:icon];
上面的代码，使icon在leftView居中显示

制造1px间隙

top和bottom的间隙非常easy做，仅仅要令leftView的height比UITextField的height少2。然后y设置为1

左側的间隙比較麻烦，首先将width设置为比UITextField的width少1。可是直接设置x为1无效。须要override下面方法：

-(CGRect) leftViewRectForBounds:(CGRect)bounds {
    CGRect iconRect = [super leftViewRectForBounds:bounds];
    iconRect.origin.x += 1;
    return iconRect;
}

制造部分圆角

制造全部的圆角比較简单，仅仅须要：

self.layer.cornerRadius = 5;

可是要制造部分圆角，就比較麻烦：

UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:leftView.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerBottomLeft cornerRadii:CGSizeMake(5, 5)];
CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
maskLayer.frame = leftView.bounds;
maskLayer.path = maskPath.CGPath;
leftView.layer.mask = maskLayer;

创建阴影

self.layer.shadowColor = [UIColor colorWithRed:132/255.0f green:214/255.0f blue:219/255.0f alpha:1.0f].CGColor;
self.layer.shadowOpacity = 0.5;
self.layer.shadowOffset = CGSizeMake(3, 3);

完整的代码

@implementation LosTextField

-(id)initWithFrame:(CGRect)frame Icon:(NSString*)iconName
{
    self = [super initWithFrame:frame];
    if (self) {
        
        CGFloat height = frame.size.height;
        
        UIView *leftView = [[UIView alloc] initWithFrame:CGRectMake(0, 1, height - 1, height - 2)];
        leftView.backgroundColor = [UIColor colorWithRed:132/255.0f green:214/255.0f blue:219/255.0f alpha:1.0f];
        
        UIImageView *icon = [[UIImageView alloc] initWithImage:[UIImage imageNamed:iconName]];
        icon.frame = CGRectMake(height / 4, height / 4, height / 2, height / 2);
        [leftView addSubview:icon];
        
        UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:leftView.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerBottomLeft cornerRadii:CGSizeMake(5, 5)];
        CAShapeLayer *maskLayer = [[CAShapeLayer alloc] init];
        maskLayer.frame = leftView.bounds;
        maskLayer.path = maskPath.CGPath;
        leftView.layer.mask = maskLayer;
        
        self.leftView = leftView;
        self.leftViewMode = UITextFieldViewModeAlways;
    }
    return self;
}

-(CGRect) leftViewRectForBounds:(CGRect)bounds {
    CGRect iconRect = [super leftViewRectForBounds:bounds];
    iconRect.origin.x += 1;
    return iconRect;
}

@end

self.username = [[LosTextField alloc] initWithFrame:CGRectMake(20, 150, 280, 40) Icon:@"login_username"];