Screen control in PowerApps
A UI element that contains one or more other controls in an app.
BackgroundImage – The name of an image file that appears in the background of a screen.
Fill – The background color of a control.
ImagePosition – The position (Fill, Fit, Stretch, Tile, or Center) of an image in a screen or a control if it isn't the same size as the image.
OnHidden – The behavior of an app when the user navigates away from a screen.
OnVisible – The behavior of an app when the user navigates to a screen.
OnStart – The behavior of the app when the user opens the app.
The formula to which this property is set runs before the first screen of the app appears. Call the Navigate function to change which screen appears first when the app starts.
You can't set context variables with the UpdateContext function because no screen has appeared yet. However, you can pass context variables in the Navigate function and create and fill a collection by using the Collect function.
When you update an app, the formula to which this property is set runs when the app is loaded into PowerApps Studio. To see the impact of changing this property, you'll need to save, close, and reload your app.
The OnStart property is actually a property of the app, not the screen. For editing convenience, you view and modify it as a property on the first screen of your app. If you remove the first screen or reorder screens, this property may become hard to find. In this case, save, close, and reload your app, and the property will reappear as a property of the first screen.
Don't know how to add, name, and configure a control?
Name the default Screen control Source, add another Screen control, and name it Target.
Set the Fill property of Target to this formula:
If("Red" in ScreenFills.Selected.Value, RGBA(255, 0, 0, 1), RGBA(54, 176, 75, 1))
Target appears in the color that you chose.
On Target, click or tap the Shape control to return to Source.
To return to the default workspace, press Esc.