屏幕适配

屏幕大小

尺寸	px	dp
MDPI	480*320	480 * 320
HDPI	960*540	640*360
XHDPI	1280*720	640*360
XXHDPI	1920*1080	640*360
XXXHDPI	2560*1440	730*410 dp

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Launcher图标大小

尺寸	px
MDPI	48*48
HDPI	72*72
XHDPI	96*96
XXHDPI	144*144
XXXHDPI	192*192

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ActionBar， Dialog，Tab，Menu图标大小

尺寸	px
MDPI	32*32
HDPI	48*48
XHDPI	64*64
XXHDPI	96*96
XXXHDPI	128*128

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Notification Bar图标大小

尺寸	px
MDPI	24*24
HDPI	36*36
XHDPI	48*48
XXHDPI	72*72
XXXHDPI	96*96

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Contextual图标大小

尺寸	px
MDPI	16*16
HDPI	24*24
XHDPI	32*32
XXHDPI	48*48
XXXHDPI	64*64

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图标下载

http://www.flaticon.com 
这个是我最常用的，资源很多（需翻墙）。

https://design.google.com/icons/ 
https://github.com/google/material-design-icons 
谷歌提供的

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图标开源项目

https://github.com/mikepenz/Android-Iconics 
强力推荐这个开源项目，我目前在用的，有了这个，图标问题完美解决。

下面是作者的原话：

If you are an app developer you will know the problem. You start an app but require many different icons, in different sizes (ldpi, mdpi, hdpi, xhdpi, xxhdpi, xxxhdpi), different colors, and different variants. 
If you get the icons as vector (.svg) or there are many changes over the time, you will always have to get the correct drawables again.

This consumes a lot of time!

Now there’s an easy, fast, and small solution for this! The Android-Iconics library.

This library allows you to include vector icons everywhere in your project. No limits are given. 
Scale with no limit, use any Color at any time, provide a contour, and many additional customizations…

Use the icons in the variation you need them.

PS：而且该项目的readme中包涵很多设计和资源下载的网站

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扁平化颜色

Material Palette调色板

这个网站可以根据你选择的颜色，自动生成Material Design对应的颜值 
http://www.materialpalette.com/blue/blue