android icon 大小设计原则
Launcher 36 x 36 px 48 x 48 px 72 x 72 px
Menu 36 x 36 px 48 x 48 px 72 x 72 px
Status Bar 24 x 24 px 32 x 32 px 48 x 48 px
Tab 24 x 24 px 32 x 32 px 48 x 48 px
Dialog 24 x 24 px 32 x 32 px 48 x 48 px
List View 24 x 24 px 32 x 32 px 48 x 48 px
