[MaterialAlertDialogBuilder] Rounded corners for AlertDialog pre Android P

Hi, thanks for the great work on Material Components.

Currently I’m facing a problem with MaterialAlertDialogBuilder. I’d like to style my AlertDialogs consistently across Android versions but setting a dialog corner radius is only possible from Android P onwards, since MaterialAlertDialogBuilder is using android.R.attr.dialogCornerRadius.

If the dialogCornerRadius attribute from AppCompat with R.attr.dialogCornerRadius was used instead, it would be possible to define a corner radius for versions < P as well.

Right now, I work around this issue by supplying a custom drawable with rounded corners to the builder in setBackground, which is a bit of a hassle.

[SamStenner]

@dominikgold So I’ve found a good, backwards compatible solution.

Create the following styles in your styles.xml like so:

<style name="MaterialAlertDialog.Rounded" parent="ThemeOverlay.MaterialComponents.MaterialAlertDialog">
    <item name="shapeAppearanceOverlay">@style/ShapeAppearanceOverlay.MaterialAlertDialog.Rounded</item>
</style>

<style name="ShapeAppearanceOverlay.MaterialAlertDialog.Rounded" parent="">
    <item name="cornerSize">10dp</item>
</style>

When instantiating your MaterialAlertDialogBuilder, pass it the resource ID of the first style, like this:

new MaterialAlertDialogBuilder(getContext(), R.style.MaterialAlertDialog_Rounded)

And now you can easily change the corner radius with the ‘cornerSize’ attribute in the style. Hope this helps!

[leticiarossi]

To have the change not affect the button shapes, you can do as follows:

<style name="ThemeOverlay.MaterialAlertDialog.Rounded" parent="ThemeOverlay.MaterialComponents.MaterialAlertDialog">
    <item name="alertDialogStyle">@style/MaterialAlertDialog.Rounded</item>
</style>

<style name="MaterialAlertDialog.Rounded" parent="MaterialAlertDialog.MaterialComponents">
    <item name="shapeAppearance">@style/ShapeAppearance.MaterialAlertDialog.Rounded</item>
</style>

<style name="ShapeAppearance.MaterialAlertDialog.Rounded" parent="">
    <item name="cornerSize">10dp</item>
</style>

and in your theme set materialAlertDialogTheme to your ThemeOverlay.MaterialAlertDialog.Rounded to change all of your dialogs!