Bitmap和Drawable



Bitmap - 位图，一般位图的文件格式后缀为bmp，编码器有很多，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，即存储效率低。

将其理解为一种存储对象比较好。

Drawable - 作为Android平台下通用的图形对象，它可以装载常用格式的图像，比如GIF、PNG、JPG，当然也支持BMP，除此之外，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.

Drawable的 API定义如下:

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。如下：

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在内存的占用和绘制速度这两个关键的点上优于Bitmap。