@Deprecated

This lua implementation is deprecated now and contains bug, we made a new implementation in Java and are waiting for it to be open source!

OnBackInvokedLua

OnBackInvokedCallback wrapper for Androlua+, compatible with Android 6.0 - 14 (partial tested: 12 - 14), onBackPressed or onKeyUp(Down)(old implementation) migration support.

Predictive back gesture

Android 13 (API level 33) introduces a predictive back gesture for Android devices such as phones, large screens, and foldables. It is part of a multi-year release; when fully implemented, this feature will let users preview the destination or other result of a back gesture before fully completing it, allowing them to decide whether to continue or stay in the current view.

documentations

• Predictive back design
• Add support for the predictive back gesture
• Add support for built-in and custom predictive back animations

Module APIs documentation

• backdispatcher.lua - equivalent to OnBackInvokedDispatcher.
• windowcallback.lua - OnKeyDown/OnBackPressed

Note: Other files are not documented, see comments for more information.

System APIs documentation

• OnBackInvokedCallback - back event interception (animated OnBackAnimationCallback)
• OnBackInvokedDispatcher - key event host

Note: Android 13 doesn't make the predictive back gesture visible to users, but it does provide an early version of the UI as a developer option for testing. Google plans to make this UI available to users in a future Android release. In the meantime, we strongly recommend updating your app to ensure you get the latest updates.

---

Add support for the predictive back gesture

this module provides a migration path to properly intercept back navigation, which involves replacing back interceptions from KeyEvent.KEYCODE_BACK and any classes with onBackPressed methods such as Activity and Dialog with the new system Back APIs. If your app implements custom back behavior, you can migrate your project with this module.

Note: KeyEvent.KEYCODE_BACK is not deprecated as there are some supported use cases of KeyEvent.KEYCODE_BACK; however, intercepting back events from KeyEvent.KEYCODE_BACK is no longer supported.

Opt in predictive back gesture

To opt in predictive back gesture, set the android:enableOnBackInvokedCallback flag to true in the <application> tag in AndroidManifest.xml. In Android 14 Beta 2 and higher, you can set it per-Activity instead of for the entire app.

<application
    ...
    android:enableOnBackInvokedCallback="true"
    ... >
...
</application>

If you don't provide a value, it defaults to false and does the following:

• Disables the predictive back gesture system animation.
• Ignores OnBackInvokedCallback, old implement calls continue to work.

After opting in, your app displays animations for back-to-home, cross-activity, and cross-task.

Add proxy classes for luajava.override

Note: This is not a standard Android Studio/IntelliJ IDEA/... project, please move files manually.

If the object returned by luajava.override, luajava.new has a wrong type, add classes in java/ or dex in libs/ to your project.

• BackInvokedCallback.java
• BackAnimationCallback.java

If you have changed class path, don't forget to modify in backdispatcher.lua!!!

Note: If your luajava fixed luajava.override, luajava.new object cast problem, you can ignore this step.

Migrate to module API

1. Use backdispatcher.lua(this module) in Activity or Dialog with old implementation used.

2. Register your custom back logic with this module. This prevents the current Activity from being finished, and your callback gets a chance to react to the Back action once the user completes the system back navigation.

3. Unregister the callback when ready to stop intercepting the back gesture. Otherwise, users may see undesirable behavior when using a system back navigation—for example, "getting stuck" between views and forcing them to force quit your app.

Here’s an example of how to migrate logic out of old implementation:

local backDispatcher = require"backdispatcher"

--you can register in onCreate, onStart or any back stack changes

--NOTICE
--this method will throw if tag or priority already exists
backDispatcher.register(
  activity,
  "finish_interception",--callback tag,
  function(dispatcher, context, tag)
    --[[
      onBackPressed logic goes here - For instance:
      Prevents closing the app to go home screen when in the
      middle of entering data to a form
      or from accidentally leaving a fragment with a WebView in it
    
      Unregistering the callback to stop intercepting the back gesture:
      When the user transitions to the topmost screen (activity, fragment)
      in the BackStack, unregister the callback by calling
    ]]
    dispatcher.unregister(context, tag)
    --or
    --dispatcher.setEnabled(context, tag, false)
  end,
  backDispatcher.PRIORITY_DEFAULT--callback priority
)

Done.

Note: To synchronize behavior with the new platform API, we DO NOT intercept back events by the callback's return value, so DO NOT return boolean in callbacks. You SHOULD always call unregister or setEnabled to stop intercepting back events.

Warning: If you don’t update your app by the next major version of Android following 13, users will experience broken Back navigation when running your app.

---

Add support for built-in and custom predictive back animations

With Android 14, if you've already migrated your app to the new system back APIs, you can create custom in-app transitions and animations for your app's custom moments by using a set of Predictive Back Progress APIs(OnBackAnimationCallback) to develop custom in-app transitions and animations.

_{custom predictive back animation of Bottom Sheet, Side Sheet, Search components, MDC Android, gif converted from material.io.}

Note: Learn how to design custom in-app transitions and animations.

Here's an example of how you might implement this feature:

--local BackEvent = luajava.bindClass"android.window.BackEvent"
local backDispatcher = require"backdispatcher"

--TODO
--your view here
local view
local screenWidth = luajava.bindClass"android.content.res.Resources".getSystem().getDisplayMetrics().widthPixels
local maxXShift = screenWidth / 20

backDispatcher.register(
  activity,
  "custom_back_animation",
  {
    onBackProgressed=function(backEvent)
      local progress = backEvent.getProgress()
      local translation = progress * maxXShift
      local scale = 1 - 0.1 * backEvent.progress
      view.setTranslationX(backEvent.getSwipeEdge() == backEvent.EDGE_LEFT and translation or -translation)
        .setScaleX(scale).setScaleY(scale)
    end,
    onBackInvoked=function(dispatcher, context, tag)
      --Do something after the back gesture completes.
    end,
    onBackCancelled=function()
      --TODO
      --reset view's position and scale
    end,
    onBackStarted=function()
      --a back gesture started
    end
  },
  backDispatcher.PRIORITY_DEFAULT
)

Add custom activity transitions on Android 14 and higher

To ensure that custom Activity transitions support predictive back on Android 14 and higher, you can use overrideActivityTransition instead of overridePendingTransition. This means that the transition animation plays as the user swipes back.

To provide an example of how this might work, imagine a scenario in which Activity B is on top of Activity A in the back stack. You would handle custom Activity animations in the following way:

• Call either opening or closing transitions within Activity B's onCreate method.
• When the user navigates to Activity B, use OVERRIDE_TRANSITION_OPEN. When the user swipes to navigate back to Activity A, use OVERRIDE_TRANSITION_CLOSE.
• When specifying OVERRIDE_TRANSITION_CLOSE, the enterAnim is Activity A's enter animation and the exitAnim is Activity B's exit animation.

Note: If exitAnim isn't set or is set to 0, the default cross-activity predictive animation (shown in the preceding video clip) plays instead.

---

Test the predictive back gesture animation

Starting with the Android 13 final release, you should be able to enable a developer option to test the back-to-home animation.

To test this animation, complete the following steps:

1. On your device, go to Settings > System > Developer options.
2. Select Predictive back animations.
3. Launch your updated app, and use the back gesture to see it in action.

Note: OnBackInvokedCallback is always called regardless of the enable state of Predictive back animations. In other words, disabling the system animation doesn't affect your app's back handling logic if it uses OnBackInvokedCallback.

---

Copyright (C) 2018-2023 The AGYS Windmill Open Source Project

	Licensed under the Apache License, Version 2.0 (the "License");
	you may not use this file except in compliance with the License.
	You may obtain a copy of the License at

		http://www.apache.org/licenses/LICENSE-2.0

	Unless required by applicable law or agreed to in writing, software
	distributed under the License is distributed on an "AS IS" BASIS,
	WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
	See the License for the specific language governing permissions and
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