Insets就是css中的padding

我们给UITextField设置了leftView，目的是在文本输入框左侧显示一个图标。但是在ios7里，这个图标会紧紧地挨着TextField的左边框，很不美观，所以就希望设置一个Insets。但是直接设置ImageView的bounds不行，需要用下面这个方法：

@interface YLSTextField : UITextField

-(id)initWithFrame:(CGRect)frame Icon:(UIImageView*)icon;

@end

@implementation YLSTextField

-(id)initWithFrame:(CGRect)frame Icon:(UIImageView*)icon
{
    self = [super initWithFrame:frame];
    if (self) {
        self.leftView = icon;
        self.leftViewMode = UITextFieldViewModeAlways;
    }
    return self;
}

-(CGRect) leftViewRectForBounds:(CGRect)bounds {
    CGRect iconRect = [super leftViewRectForBounds:bounds];
    iconRect.origin.x += 10;// 右偏10
    return iconRect;
}

@end

UIImage *usernameImage = [UIImage imageNamed:@"user"];
UIImageView *usernameIcon = [[UIImageView alloc] initWithImage:usernameImage];
usernameIcon.frame = CGRectMake(0, 0, 20, 20);
        
self.username = [[YLSTextField alloc] initWithFrame:CGRectMake(0, 0, 240, 30) Icon:usernameIcon];
self.username.placeholder = @"用户名";
self.username.borderStyle = UITextBorderStyleRoundedRect;
self.username.clearButtonMode = UITextFieldViewModeWhileEditing;
[self.username setKeyboardType:UIKeyboardTypeNumberPad];