Access progress manually

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The PredictiveBackHandler composable in Jetpack Compose lets you intercept the back gesture and access its progress. You can react to the user's back gesture in real-time, creating custom animations or behaviors based on how far the user swipes.

To use the PredictiveBackHandler, ensure you are using androidx.activity:activity:1.6.0 or higher.

PredictiveBackHandler provides a Flow<BackEventCompat> that emits events representing the progress of the back gesture. Each event contains information such as:

• progress: A float value between 0 and 1 indicating the progress of the back gesture (0 = gesture started, 1 = gesture completed).
• touchX and touchY: The X and Y coordinates of the touch event.

The following snippet shows basic usage of PredictiveBackHandler:

PredictiveBackHandler(true) { progress: Flow<BackEventCompat> ->
    // code for gesture back started
    try {
        progress.collect { backEvent ->
            // code for progress
            boxScale = 1F - (1F * backEvent.progress)
        }
        // code for completion
        boxScale = 0F
    } catch (e: CancellationException) {
        // code for cancellation
        boxScale = 1F
    }
}
PredictiveBackSnippets.kt

Example: Integrate with a navigation drawer

This example demonstrates how to implement a custom in-app animation using PredictiveBackHandler to create a smooth interaction with a navigation drawer in response to back gestures in JetLagged:

In this example, PredictiveBackHandler is used to:

• Track the progress of the back gesture.
• Update the translationX of the drawer based on the gesture progress.
• Use a velocityTracker to smoothly open or close the drawer based on the gesture velocity when the gesture is completed or canceled.