关于mipmap和drawable使用

在stackoverflow看到关于这两个目录使用比较好的解释：

Here is my two cents in trying to explain the difference. There are two cases you deal with when working with images in Android:

You want to load an image for your device density and you are going to use it “as is”, without changing its actual size. In this case you should work with drawables and Android will give you the best fitting image.

You want to load an image for your device density, but this image is going to be scaled up or down. For instance this is needed when you want to show a bigger launcher icon, or you have an animation, which increases image’s size. In such cases, to ensure best image quality, you should put your image into mipmap folder. What Android will do is, it will try to pick up the image from a higher density bucket instead of scaling it up. This will increase sharpness (quality) of the image.

Thus, the rule of thumb to decide where to put your image into would be:

Launcher icons always go into mipmap folder.

Images, which are often scaled up (or extremely scaled down) and whose quality is critical for the app, go into mipmap folder as well.

All other images are usual drawables.

意思就是当图片不需要改变尺寸的时候，图片放drawable，如果图片需要改变尺寸，比如动画里面需要放大，就要放到mipmap，这时候如果图片放到，会自动加载更高尺寸的目录里面的图片，从而避免失真.