android widget的预览图

android 3.0以上支持widget的预览图了

<?xml version="1.0" encoding="utf-8"?>
<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:updatePeriodMillis="0"
    android:initialLayout="@layout/widget_large"
    android:previewImage="@drawable/widget_large_preview"
    android:minWidth="290dp"
    android:minHeight="296dp"
    >
</appwidget-provider>