     var isFromNet:Bool = true
     
     //占位图
-    var placeholderImage:String = "ic_place"
+    var placeholderImage:String = placeholder
     
     //设置图片资源url字符串。
     var imgUrls = NSArray(){

        //通过打印可以看到此时cell的frame就是我们在flowLayout中设置的结果
        print("self.collectionView:\(String(describing: self))")
        imageView = UIImageView.init(frame: self.bounds)
        imageView?.contentMode = .scaleAspectFill
        contentView.addSubview(imageView!)
    }

    
    convenience init(frame:CGRect,imageUrls:NSArray) {
        self.init(frame: frame, collectionViewLayout: HHCollectionViewFlowLayout.init())
        imgUrls = imageUrls
    }
    
    override init(frame: CGRect, collectionViewLayout layout: UICollectionViewLayout) {
