让UIImageView适应图片的大小

//创建imgV视图
-(void)createImgV
{
//创建视图展示
_imgV = [[UIImageView alloc] initWithFrame:CGRectZero];

_imgV.backgroundColor=[UIColor yellowColor];

//    _imgV.contentMode = UIViewContentModeScaleAspectFit;

_imgV.backgroundColor=[UIColor yellowColor];

_imgV.contentMode=UIViewContentModeScaleToFill;

[self addSubview:_imgV];
}

-(void)setImgName:(NSString *)imgName
{
_imgName = imgName;

[_imgV setImageWithURL:[NSURL URLWithString:_imgName]];

_imgV.frame=CGRectMake(0, 0, _imgV.image.size.width, _imgV.image.size.height);
}