有两种方式：
方式一：colorWithPatternImage用背景颜色设置图片

UIImageView * imageView = [[UIImageView alloc]initWithFrame:CGRectMake(20, 100, 400, 18)];
[self.view addSubview:imageView];
imageView.backgroundColor = [UIColor colorWithPatternImage:[UIImage imageNamed:@"ico_pk_bar_blue.png"]];

方式二：UIImageResizingModeTileresize图片

UIImageView * imageView = [[UIImageView alloc]initWithFrame:CGRectMake(20, 100, 400, 18)];
    [self.view addSubview:imageView];
    UIImage *image = [UIImage imageNamed:@"ico_pk_bar_blue.png"];

    UIImage * newImage = [image resizableImageWithCapInsets:UIEdgeInsetsZero resizingMode:UIImageResizingModeTile];
    
    imageView.image = newImage;