• Drawable和Bitmap的区别


    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

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  • 原文地址:https://www.cnblogs.com/hjtdlx/p/4301187.html
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