正三角

<?xml version="1.0" encoding="utf-8"?>  
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">  
    <item android:id="@+id/shape_id">  
        <!-- 正三角 -->  
        <rotate  
            android:fromDegrees="45"  
            android:toDegrees="45"  
            android:pivotX="-40%"  
            android:pivotY="80%">  
            <shape android:shape="rectangle">  
                <solid android:color="#000000"/>  
            </shape>  
        </rotate>  
    </item>  
</layer-list>

倒三角

shape_reverse_triangle.xml

<?xml version="1.0" encoding="utf-8"?>  
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">  
  
  
    <item android:id="@+id/shape_id">  
        <!-- 倒三角 -->  
        <rotate  
            android:fromDegrees="45"  
            android:toDegrees="45"  
            android:pivotX="135%"  
            android:pivotY="15%"  
            >  
            <shape android:shape="rectangle">  
                <solid android:color="#000000"/>  
            </shape>  
        </rotate>  
    </item>  
  
  
</layer-list>

使用

<ImageView
        android:layout_width="18dp"
        android:layout_height="18dp"
        android:background="@drawable/shape_reverse_triangle"
        />

效果图

源码

不懂的童鞋可以去下载源码：​