Jetpack Compose/Glance: previewLayout value

An <appwidget-provider> expects a previewLayout attribute on modern Android versions. The documentation tells us what value we should use for initialLayout, but it never mentions the previewLayout attribute. Am I supposed to try to completely rebuild my Glance UI in XML?

No, you do not need to rebuild your entire Glance UI in XML for the previewLayout attribute of <appwidget-provider>. The previewLayout is used only by the launcher or home screen to display a static preview of your widget in the picker before adding it to the home screen. It does not impact your runtime Glance-based UI.

1. Make a simple XML layout similar to the final form of the widget, for almost preview purposes.

2. It doesn't have to be interactive or dynamic - this is just a stable image shown in the widget picker.

3. This file goes to the res/ layout/ and must be referred to preview.

For Example

res/layout/widget_preview.xml

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="250dp"
    android:layout_height="100dp"
    android:orientation="vertical"
    android:background="@android:color/darker_gray"
    android:padding="16dp">

    <TextView
        android:id="@+id/title"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Widget Preview"
        android:textSize="18sp"
        android:textColor="@android:color/white" />

</LinearLayout>

res/xml/my_widget_info.xml

<appwidget-provider xmlns:android="http://schemas.android.com/apk/res/android"
    android:minWidth="250dp"
    android:minHeight="100dp"
    android:updatePeriodMillis="0"
    android:previewLayout="@layout/widget_preview"
    android:initialLayout="@layout/placeholder"
    android:resizeMode="horizontal|vertical"
    android:widgetCategory="home_screen">
</appwidget-provider>

Note: you can directly use screenshot as well in preview using the attributes

android:previewImage="@drawable/widget_big"

or for XML

android:previewLayout="@layout/widget_preview"

And finally in manifest file*

<receiver android:name=".SampleReceiver"
    android:exported="true">
    <intent-filter>
        <action android:name="android.appwidget.action.APPWIDGET_UPDATE" />
    </intent-filter>
    <meta-data
        android:name="android.appwidget.provider"
        android:resource="@xml/my_widget_info" />
</receiver>