"Race condition" when using switchTo() about alligator HOT 8 CLOSED

In what order do you call navigation method?
This order goForward, switchTo means for a navigator "go to a lock screen and then switch screens there". In that case NavigationException is expected because a lock screen can't switch screens. So an order should be opposite - switchTo, goForward. Or you can use ScreenResult if you want to switch screens after an user returns from a lock screen.

from alligator.

Yes I know but I cannot switch that order because of the implementation of the app.

The thing is:
1 - Open activity that will load a fragment with switchTo().
2 - While the activity is being opened, on the "onStart()" method, a goForward() command is executed to navigate to a LockActivity because you have to set a pincode to access the app.
3 - Before the "goForward()" is executed, the first activity is not stopped yet and the "switchTo()" command is added to the queue.
4 - Alligator executes the goForward() to the LockActivity and then when the navigation context is set, the pending switchTo() command is executed without a ScreenSwitcher added.

In my concrete implementation, as the navigation to the LockActivity is done on an external lifecycle callback, I cannot know if the LockActivity is pending to be opened from any activity. If I could access the navigation queue (at least read only), I could check if there is a goForward() pending before adding the switchTo() command.

from alligator.

Still don't understand where and when do you call switchTo().

from alligator.

I call it after onStart(), but the first activity creation lifecycle is still running when I am navigating to the LockActivity, so switchTo() is called after goForward().

from alligator.

In my opinion the best solution would be rethink how navigation to a lock screen is called. The order of navigation method calls is crucial here. It is hard to give a concrete advice because I don't know how your implementation looks like.

If I could access the navigation queue (at least read only), I could check if there is a goForward() pending before adding the switchTo() command.

I'm not sure that giving a direct access to the navigation queue is a good idea. It is supposed to be implementation detail but not a pulic api.

from alligator.

I thought about the issue some more and decided that these methods should be added to Navigator:

• boolean canExecuteCommandImmediately() - returns true if a navigator can execute a command immediately (NavigationContext is bound and a queue is empty).
• boolean hasPendingCommands() - returns true if a navigator has pending commands (a queue is not empty).

You can use it like that:

@Override
protected void onStart() {
	super.onStart();
	if (mScreenSwitcher.getCurrentFragment() == null && !mNavigator.hasPendingCommands()) {
		mNavigator.switchTo(new SomeScreen());
	}
}

Now this change is in the develop branch. Take it from jitpack.io. Give me to know if it is helpful for you. Then I will make a release.

from alligator.

That's a more robust solution! Yes is absolutely helpful, many thanks.
This library is the best solution for android navigation I've ever seen, sorry if I bother you too much with my issues but I really want to contribute to it :)

from alligator.

I am very glad. Thank you for helping to make Alligator better.
Version 2.1.0 is ready!

from alligator.