iOS 图片中间不拉伸 两边拉伸

UIImageView * dbImageView = [[UIImageView alloc]init];

 UIImage *image = [UIImage imageNamed:@"image"];

 image = [image stretchableImageWithLeftCapWidth:image.size.width * 0.7 topCapHeight:image.size.height*0.5];

dbImageView.image= image;

 //第一次拉伸宽度=最终宽度/2+原图宽度/2 

CGFloattempWidth = [UIScreen mainScreen].bounds.size.width/2+360/2;

UIGraphicsBeginImageContextWithOptions(CGSizeMake(tempWidth, 44), NO, [UIScreen mainScreen].scale);

[dbImageView.imagedrawInRect:CGRectMake(0,0, tempWidth,44)];

image =UIGraphicsGetImageFromCurrentImageContext(); 

dbImageView.image = [image stretchableImageWithLeftCapWidth:image.size.width *0.2 topCapHeight:image.size.height*0.5];

dbImageView.userInteractionEnabled=YES;

 [self.view addSubview:dbImageView];

[dbImageView mas_makeConstraints:^(MASConstraintMaker *make) {

     make.left.offset(0);

     make.right.offset(0);

     make.height.offset(64);

     make.bottom.offset(0)

 }];