Drawable和Bitmap的区别

以你之姓@ 2022-08-21 04:13 143阅读 0赞

Bitmap - 称作位图，一般位图的文件格式后缀为bmp，当然编码器也有很多如RGB565、RGB888。作为一种逐像素的显示对象执行效率高，但是缺点也很明显存储效率低。我们理解为一种存储对象比较好。  
    Drawable - 作为Android平下通用的图形对象，它可以装载常用格式的图像，比如GIF、PNG、JPG，当然也支持BMP，当然还提供一些高级的可视化对象，比如渐变、图形等。  
  
A bitmap is a Drawable. A Drawable is not necessarily a bitmap. Like all thumbs are fingers but not all fingers are thumbs.  
Bitmap是Drawable . Drawable不一定是Bitmap .就像拇指是指头,但不是所有的指头都是拇指一样.  
  
The API dictates: API规定:  
  
Though usually not visible to the application, Drawables may take a variety of forms: 尽管通常情况下对于应用是不可见的,Drawables 可以采取很多形式:  
  
Bitmap: the simplest Drawable, a PNG or JPEG image. Bitmap: 简单化的Drawable, PNG 或JPEG图像.   
Nine Patch: an extension to the PNG format allows it to specify information about how to stretch it and place things inside of it.  
Shape: contains simple drawing commands instead of a raw bitmap, allowing it to resize better in some cases.  
Layers: a compound drawable, which draws multiple underlying drawables on top of each other.  
States: a compound drawable that selects one of a set of drawables based on its state.  
Levels: a compound drawable that selects one of a set of drawables based on its level.  
Scale: a compound drawable with a single child drawable, whose overall size is modified based on the current level.

小结：

对比项          显示清晰度      占用内存     支持缩放    支持色相色差调整      支持旋转     支持透明色       绘制速度           支持像素操作  
  
Bitmap          相同                大                 是                是                            是                是                     慢                      是  
Drawable       相同                小                 是               否                            是                 是                     快                      否

Drawable在内存占用和绘制速度这两个非常关键的点上胜过Bitmap

转自：http://iaiai.iteye.com/blog/1991225

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所以，如果仅仅是用ImageView显示一张图片的话，我们就用 Drawable 可能更好一些。

如果需要旋转等图片处理，就一定需要用到Bitmap了。