launchSingleTop属性跳转页面问题

[hele-jeremy]

launchSingleTop属性跳转页面在不同的手机上有不同的 表现,某些手机会闪一下,某些机型会直接显示上一级的 页面

原因为hide隐藏的其实就是DFragment，而add添加的fragment其实也是Dfragment因此在同一个FragmentTransation中隐藏和添加同一个Fragment会有问题的,if (mBackStack.size() > 0 && mFragmentManager.getFragments().size() > 0) {
Log.d("Nav"," --Hide --Add");
ft.hide(mFragmentManager.getFragments().get(mBackStack.size() - 1));
ft.add(mContainerId, frag);
}
我修改了FragmentNavigator的navigate方法相当是launchsingletop的情况下,不将新创建的fragmet入栈:
public NavDestination navigate(@nonnull Destination destination, @nullable Bundle args,
@nullable NavOptions navOptions, @nullable Navigator.Extras navigatorExtras) {
if (mFragmentManager.isStateSaved()) {
Log.i(TAG, "Ignoring navigate() call: FragmentManager has already"
+ " saved its state");
return null;
}
String className = destination.getClassName();
if (className.charAt(0) == '.') {
className = mContext.getPackageName() + className;
}
final Fragment frag = instantiateFragment(mContext, mFragmentManager, className, args);
frag.setArguments(args);
final FragmentTransaction ft = mFragmentManager.beginTransaction();

    int enterAnim = navOptions != null ? navOptions.getEnterAnim() : -1;
    int exitAnim = navOptions != null ? navOptions.getExitAnim() : -1;
    int popEnterAnim = navOptions != null ? navOptions.getPopEnterAnim() : -1;
    int popExitAnim = navOptions != null ? navOptions.getPopExitAnim() : -1;
    if (enterAnim != -1 || exitAnim != -1 || popEnterAnim != -1 || popExitAnim != -1) {
        enterAnim = enterAnim != -1 ? enterAnim : 0;
        exitAnim = exitAnim != -1 ? exitAnim : 0;
        popEnterAnim = popEnterAnim != -1 ? popEnterAnim : 0;
        popExitAnim = popExitAnim != -1 ? popExitAnim : 0;
        ft.setCustomAnimations(enterAnim, exitAnim, popEnterAnim, popExitAnim);
    }


    final @IdRes int destId = destination.getId();
    final boolean initialNavigation = mBackStack.isEmpty();
    // TODO Build first class singleTop behavior for fragments
    final boolean isSingleTopReplacement = navOptions != null && !initialNavigation
            && navOptions.shouldLaunchSingleTop()
            && mBackStack.peekLast() == destId;

    Log.d("testnav", " --isSingleTopReplacement --- " + isSingleTopReplacement);

    //TODO Tip 1: Solve the unexpected display of popUpToInclusive under the add hide solution
    //TODO Tip 2: Increase fault tolerance to deal with incorrectly-timed jumps in the case of nested sub-fragments
    Log.d("testnav", " --mBackStack.size:" + mBackStack.size()
            + " getFragments().size():" + mFragmentManager.getFragments().size());
    if (mBackStack.size() > 0 && mFragmentManager.getFragments().size() > 0) {
        Log.d("testnav", " --Add --- " + frag);
        Fragment hideFrag = mFragmentManager.getFragments().get(mBackStack.size() - 1);
        Log.d("testnav", " --Hide --- " + hideFrag);

        if (isSingleTopReplacement) {
            hideFrag.setArguments(args);
            ft.setMaxLifecycle(hideFrag, Lifecycle.State.RESUMED);
        } else {
            ft.hide(hideFrag);
            ft.add(mContainerId, frag);
            ft.setPrimaryNavigationFragment(frag);
        }

    } else {
        Log.d("testnav", " --Replace --- " + frag);
        ft.replace(mContainerId, frag);
        ft.setPrimaryNavigationFragment(frag);
    }

// ft.setPrimaryNavigationFragment(frag);

    boolean isAdded;
    if (initialNavigation) {
        isAdded = true;
    } else if (isSingleTopReplacement) {
        // Single Top means we only want one instance on the back stack

// if (mBackStack.size() > 1) {
// // If the Fragment to be replaced is on the FragmentManager's
// // back stack, a simple replace() isn't enough so we
// // remove it from the back stack and put our replacement
// // on the back stack in its place
// mFragmentManager.popBackStack(
// generateBackStackName(mBackStack.size(), mBackStack.peekLast()),
// FragmentManager.POP_BACK_STACK_INCLUSIVE);
// ft.addToBackStack(generateBackStackName(mBackStack.size(), destId));
// }
isAdded = false;
} else {
ft.addToBackStack(generateBackStackName(mBackStack.size() + 1, destId));
isAdded = true;
}
if (navigatorExtras instanceof Extras && !isSingleTopReplacement) {
Extras extras = (Extras) navigatorExtras;
for (Map.Entry<View, String> sharedElement : extras.getSharedElements().entrySet()) {
ft.addSharedElement(sharedElement.getKey(), sharedElement.getValue());
}
}
ft.setReorderingAllowed(true);
ft.commit();
// The commit succeeded, update our view of the world
if (isAdded) {
mBackStack.add(destId);
return destination;
} else {
return null;
}
}

[hele-jeremy]

原生的navigation跳转页面时replace替换Fragment的因此launchSingleTop只能工作在自己跳转自己页面的情况,因此在原生的情况下,机制是launchSingleTop每次都会新建一个新的页面fragment实例,并将上一个自己页面的fragment实例给popupbackstatck 出栈并且将新创建的fragment页面实例给入栈,而改为了hide的机制后, launchSingleTop不应该将老的上一个页面给出栈,而是应该 继续保持老的fragment页面实例在栈中

[KunMinX]

@hele-jeremy
感谢你的分享，经测试，上述代码可实现预期效果，且在目前已知场景下皆未产生副作用，
为此可以邀请你 pull request 上述设计吗？这可以让你的这次分享出现在贡献名单中。开源不是一个人的战斗，我们希望每位贡献者都能出现在贡献者名单。

[hele-jeremy]

已提交pr