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FlutterFragment predictive back #52302

Merged
merged 12 commits into from
May 28, 2024
Merged

FlutterFragment predictive back #52302

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89629fb
Seems to work whether Flutter is the first acitivty or not
justinmc Aug 18, 2023
bf4e1ec
Work with original onBackPressed mechanics
justinmc Aug 18, 2023
c396216
Merge branch 'main' into flutter-fragment-predictive-back
justinmc Apr 22, 2024
1ae637d
Fix from math1man review https://github.com/flutter/engine/pull/44865…
justinmc Apr 22, 2024
7cd3383
popSystemNavigator should restore onBackPressedCallback to original s…
justinmc Apr 23, 2024
3733332
Test that popSystemNavigator preserves enabled state
justinmc Apr 24, 2024
0d95e27
An attempt at testing the callback being enabled/disabled, but not wo…
justinmc Apr 24, 2024
6d69cfc
Merge branch 'main' into flutter-fragment-predictive-back
justinmc May 16, 2024
c06300a
Fix flipped logic, and add comments explaining what's going on
justinmc May 17, 2024
48765ee
Merge branch 'main' into flutter-fragment-predictive-back
justinmc May 28, 2024
c785e98
Clarify comment
justinmc May 28, 2024
1ff7c32
Whoops, should have gotten this in the merge commit
justinmc May 28, 2024
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13 changes: 13 additions & 0 deletions shell/platform/android/io/flutter/embedding/android/FlutterFragment.java
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Original file line number Diff line number Diff line change
Expand Up @@ -1056,6 +1056,11 @@ public void onAttach(@NonNull Context context) {
delegate.onAttach(context);
if (getArguments().getBoolean(ARG_SHOULD_AUTOMATICALLY_HANDLE_ON_BACK_PRESSED, false)) {
requireActivity().getOnBackPressedDispatcher().addCallback(this, onBackPressedCallback);
// By default, Android handles backs, and predictive back is enabled. This
// can be changed by calling setFrameworkHandlesBack. For example, the
// framework will call this automatically in a typical app when it has
// routes to pop.
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I am still confused by this code. It looks like we are on a true branch of ARG_SHOULD_AUTOMATICALLY_HANDLE_ON_BACK_PRESSED.
Is this just saying that onBackPressedCallback.setEnabled should be the opposite of the argument passed to ARG_SHOULD_AUTOMATICALLY_HANDLE_ON_BACK_PRESSED?

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I'm going to push a commit to reword this comment to try to make it more clear.

ARG_SHOULD_AUTOMATICALLY_HANDLE_ON_BACK_PRESSED means that predictive back is enabled. onBackPressedCallback enabled means that Flutter is handling back gestures (typically because Flutter has Flutter routes to on its navigation stack). Disabled means that Android is handling back gestures, so it will either pop the Activity or go back to the phone's home screen.

So when the app starts, by default we let Android handle backs. If/when the Flutter app wants to change this, it calls setFrameworkHandlesBack and enables this callback.

onBackPressedCallback.setEnabled(false);
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You probably also need to update the implementation of popSystemNavigator() to restore the previous state of the callback-enablement, instead of unconditionally re-enabling it on line 1673.

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@math1man Thanks for jumping back in here, I've been trying to catch back up on your comments from the last PR. Pushing a fix for that now.

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No worries. Honestly, I think besides this comment everything looks good. Happy to look into anything specific you might be concerned about though.

}
context.registerComponentCallbacks(this);
}
Expand Down Expand Up @@ -1673,6 +1678,14 @@ public boolean popSystemNavigator() {
return false;
}

@Override
public void setFrameworkHandlesBack(boolean frameworkHandlesBack) {
if (getArguments().getBoolean(ARG_SHOULD_AUTOMATICALLY_HANDLE_ON_BACK_PRESSED, false)) {
return;
}
onBackPressedCallback.setEnabled(frameworkHandlesBack);
}

@VisibleForTesting
@NonNull
boolean shouldDelayFirstAndroidViewDraw() {
Expand Down
10 changes: 4 additions & 6 deletions shell/platform/android/io/flutter/embedding/android/FlutterFragmentActivity.java
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Original file line number Diff line number Diff line change
Expand Up @@ -518,6 +518,7 @@ protected FlutterFragment createFlutterFragment() {
? TransparencyMode.opaque
: TransparencyMode.transparent;
final boolean shouldDelayFirstAndroidViewDraw = renderMode == RenderMode.surface;
final boolean shouldAutomaticallyHandleOnBackPressed = true;

if (getCachedEngineId() != null) {
Log.v(
Expand All @@ -542,6 +543,7 @@ protected FlutterFragment createFlutterFragment() {
.shouldAttachEngineToActivity(shouldAttachEngineToActivity())
.destroyEngineWithFragment(shouldDestroyEngineWithHost())
.shouldDelayFirstAndroidViewDraw(shouldDelayFirstAndroidViewDraw)
.shouldAutomaticallyHandleOnBackPressed(shouldAutomaticallyHandleOnBackPressed)
.build();
} else {
Log.v(
Expand Down Expand Up @@ -577,6 +579,7 @@ protected FlutterFragment createFlutterFragment() {
.transparencyMode(transparencyMode)
.shouldAttachEngineToActivity(shouldAttachEngineToActivity())
.shouldDelayFirstAndroidViewDraw(shouldDelayFirstAndroidViewDraw)
.shouldAutomaticallyHandleOnBackPressed(shouldAutomaticallyHandleOnBackPressed)
.build();
}

Expand All @@ -592,6 +595,7 @@ protected FlutterFragment createFlutterFragment() {
.transparencyMode(transparencyMode)
.shouldAttachEngineToActivity(shouldAttachEngineToActivity())
.shouldDelayFirstAndroidViewDraw(shouldDelayFirstAndroidViewDraw)
.shouldAutomaticallyHandleOnBackPressed(shouldAutomaticallyHandleOnBackPressed)
.build();
}
}
Expand All @@ -616,12 +620,6 @@ protected void onNewIntent(@NonNull Intent intent) {
super.onNewIntent(intent);
}

@Override
@SuppressWarnings("MissingSuperCall")
public void onBackPressed() {
flutterFragment.onBackPressed();
}

@Override
public void onRequestPermissionsResult(
int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
Expand Down