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

// 设置端盖的值

CGFloat top = 10;

CGFloat left = 10;

CGFloat bottom = 10;

CGFloat right = 10;

// 设置端盖的值

UIEdgeInsets edgeInsets = UIEdgeInsetsMake(top, left, bottom, right);

// 设置拉伸的模式

UIImageResizingMode mode = UIImageResizingModeStretch;

// 拉伸图片

UIImage *newImage = [image resizableImageWithCapInsets:edgeInsets resizingMode:mode];

_bgImgView.image = newImage;