Drawable Resources

A drawable resource is a general concept for a graphic that can be drawn to the screen.

There are several different types of drawables:

Bitmap File
Nine-Patch File
Layer List
State List
Level List
Transition Drawable
Inset Drawable
Clip Drawable
Shape Drawable

Layer List

A LayerDrawable is a drawable object that manages an array of other drawables. Each drawable in the list is drawn in the order of the list—the last drawable in the list is drawn on top.

Each drawable is represented by an <item> element inside a single <layer-list> element.

<layer-list> This must be the root element. Contains one or more ｀｀ elements.

命名空间：

xmlns:android="http://schemas.android.com/apk/res/android"

<item>Must be a child of a element. Accepts child ｀｀ elements.

example

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
        <shape>
            <solid android:color="#ff0000" />
        </shape>
    </item>


    <item android:left="2dp" android:right="2dp" android:top="2dp" android:bottom="2dp">
        <shape>
            <solid android:color="#ffffff" />
        </shape>
    </item>
</layer-list>

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item>
      <bitmap android:src="@drawable/android_red"
        android:gravity="center" />
    </item>
    <item android:top="10dp" android:left="10dp">
      <bitmap android:src="@drawable/android_green"
        android:gravity="center" />
    </item>
    <item android:top="20dp" android:left="20dp">
      <bitmap android:src="@drawable/android_blue"
        android:gravity="center" />
    </item>
</layer-list>

State List

最常用的selector

Level List

Android 电量图标显示用到的技术

Transition Drawable

Inset Drawable

Clip Drawable

Scale Drawable

Shape Drawabel

android:shape=["rectangle" | "oval" | "line" | "ring"]　缺省值是rectangle

<stroke>边框颜色

<solid>填充颜色

<padding>不知道什么效果

<gradient>填充渐变颜色

<corners>设置圆角
如何设置特定上下左右位置圆角 Every corner must (initially) be provided a corner radius greater than 1, or else no corners are rounded. If you want specific corners to not be rounded, a work-around is to use android:radius to set a default corner radius greater than 1, but then override each and every corner with the values you really want, providing zero (“0dp”) where you don’t want rounded corners.

<?xml version="1.0" encoding="utf-8"?>
<!-- android:shape默认缺省值：rectangle -->
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <!--<gradient-->
    <!--android:startColor="#FFFF0000"-->
    <!--android:endColor="#80FF00FF"-->
    <!--android:angle="45"/>-->
    <!--<padding android:left="7dp"-->
    <!--android:top="7dp"-->
    <!--android:right="7dp"-->
    <!--android:bottom="7dp" />-->
    <solid android:color="@color/colorPrimary"/>
    <stroke
        android:color="@color/colorAccent"
        android:width="2px"/>

</shape>

yeshu blog

Android Drawable Resources