hi i have an application
A is launcher activity from that i create B activity. From B i want to go back to A without deleting the instance of B(so no finish) then i want to create a new instance of B lets call it B2. And from A i want to be able to show B or B2 without recreating them.
again i stress that B,B2 are the same class just diffrent instances.
from B when i want to go to A i thought of using
Intent myIntent = new Intent(getBaseContext(), MainAct.class);
myIntent.setFlags(Intent.FLAG_ACTIVITY_SINGLE_TOP);
startActivity(myIntent);
but i think that its a mistake because it will clear other instances.
what intent must i use in the cases?
in c# windows application we would do B.hide();A.show(). then from A we could do
A.hide(); B.SHOW() or B1.show();
how can i do that in android please?
If B is an Activity, you can't have two different instances of it.
You can have 2 different Activities that extend the same class, but you've indicated you don't want that.
You need to find a way to change the appearance and behavior of B rather than creating a new instance.
Please consider reading about the Activity Lifecycle.
use FLAG_ACTIVITY_REORDER_TO_FRONT
from the doc
If set in an Intent passed to Context.startActivity(), this flag will
cause the launched activity to be brought to the front of its task's
history stack if it is already running.
Related
I am having two activities, Activity A and activity B.
Activity A starts activity B.
So, the activity stack after some interactions will look like A -> B -> A -> B.
The problem:
I need to go the first activity A in the stack from activity B (last B in the stack). I am using FLAG_CLEAR_TOP as well as Intent.FLAG_ACTIVITY_NEW_TASK for achieving the same.
Right now, the activity A (stack pos 3) will be shown from activity B, but when I press back button, the activity B will be shown again (since activity B (stack pos 2) is already there in the stack).
How do I overcome this issue?
PS: I tried using launchMode singleInstance and singleTask for activities A and B, but that solution doesn't work for my app.
Thanks in advance.
Add finish (); after switching activites like
Intent intent = new Intent (activity_a.this, activity_b.class);
startActivity(intent);
finish ();
Avoid creating multiple instances of activities if possible. Android isn't designed to allow you to identify (and return to) a specific instance of an Activity in the stack, if you have multiple instances of the same Activity in the stack.
Depending on your application, there are different ways to solve the problem.
One way that may work for you is to use <activity-alias>, which allows you to reuse an existing Activity implementation by another name.
Another way would be to create another Activity class, that just inherits from the original, so that you have 2 classes with exactly the same code, but with different names.
The best way is to rearchitect your application so that you only ever have one instance of each Activity alive at any given time. You can do this by rearranging the task stack using Intent.FLAG_ACTIVITY_REORDER_TO_FRONT.
Suppose I have activity instances A1, B1, A2, B2, C1 of activities A, B, C in stack. How can I traverse to Activity instance B1 from C1?
Let us generalize there will be 'n' number of activities between B1 and C1.
I don't want to create a new instance of B from C1.
This is actually a very bad architecture for Android. If you create multiple instances on an Activity, there is no way to specifically address them, for example: "Go back to the first instance of ActivityB". Android isn't designed like this.
You should avoid creating multiple instances of an Activity. It is beter to use the same instance and just create the "illusion" of multiple instances by swapping out the underlying data and maybe adding a state transition on the display so that it looks like you are starting another Activity.
Another possible solution would be to use a lot of startActivityForResult() and return information to the calling Axctivity about what to do next.
For more details see (even though these questions are specifically about using FLAG_ACTIVITY_REORDER_TO_FRONT, the problem is still basically the same):
Managing Android Activity stack: bring specific activity instance to front
Multiple activity instances and FLAG_ACTIVITY_REORDER_TO_FRONT
Bring an activity to front using FLAG_ACTIVITY_REORDER_TO_FRONT
Use Flags with Intent.
official Docs: https://developer.android.com/guide/components/tasks-and-back-stack.html
pass the flag along with Intent
FLAG_ACTIVITY_CLEAR_TOP
also you can paas multiple FLags in a single Intent according to your need.
Hope this helps.
I'm new to Android development and here's my problem:
I have 2 activities: A and B.
From A, I call B via startActivity(new Intent(A.this, B.class))
From B, I do some things and return to A the same way: startActivity(new Intent(B.this, A.class))
However, when on new-A I press "Back" button, first I see B class and then the old (unchanged version) of A class.
I've tried placing finish(); inside onPause() method. However, then my Activity crashes on orientation change.
How can I properly control activity backstack? Thanks in advance.
When you call startActivity without any additional flags, you will create a new instance of the Activity specified. This means that your back stack ends up looking like this:
A -> B -> A(2)
You have two options:
First option, you can add flags on the Intent that instructs it to reorder A to the front if it is already present in the back stack. Note that this will not close B; you have to call finish() in B afterward.
Intent intent = new Intent(B.this, A.class);
intent.addFlags(Intent.FLAG_ACTIVITY_REORDER_TO_FRONT);
startAcvitiy(intent);
finish();
Second option is to use startActivityForResult instead of startActivity in A and have Activity B pass a result back to A. I think this is much cleaner and it gives you a very easy way to react to what happened when B was finished (e.g. you can update your UI). See this guide from the Android developers site.
Either StartActivityForResult or think about using fragments. If you need to jump between activities think about why you are doing this? If you are passing info between the two then there are a couple of options. Fragments give you the option and you can hold the data on the Activity that hosts the fragments or you can have a Singleton living in an Application class that you would extend.
Read about activity lifecycle - here. You have to implement saving of instance.
It sounds like that rather than calling startActivity in to go back to A, you can just call instead finish();. This will land you back on your previous Activity.
Alternatively you can accomplish the same if you use FLAG_ACTIVITY_CLEAR_TOP:
Intent intent = new Intent(B.this, A.class);
intent.addFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(intent);
Regarding the accepted answer's suggestion to use FLAG_ACTIVITY_REORDER_TO_FRONT - for your case it really doesn't matter. but in a slightly different case where you have A->B->C and you use REORDER to go back to A, you'd actually end up with a stack that looks like B->C->A. With CLEAR_TOP, you'd end up with just A. Point is, REORDER is meant to REORDER, CLEAR_TOP is supposed to pop the backstack. In your simple case they happen to accomplish the same, but in my opinion it's better practice to use the flags as they're intended.
I'm just learning Android programming. The way I understand it is that the services work like a stack, Is there a way for a activity to return to the first activity that started the app, instead of just the previous one.
Example, say I have 4 activities, a,b,c,d. Is there a way for activity d to have a button that would bring up activity a?? Instead of activity d going to c, and c going back to b???
You can start again activity a, but using a flag in your intent:
FLAG_ACTIVITY_REORDER_TO_FRONT
From android docs:
If set in an Intent passed to Context.startActivity(), this flag will cause the launched activity to be brought to the front of its task's history stack if it is already running.
Using this, you'll reuse the instance of activity a already running, instead of starting a new one. Note that doing this, the instances of activities b, c and d will remain in the back stack (now after activity a).
Otherwise, if you want to finish this activities (and remove them from the back stack) you can start activity a (from d) with this other flag:
FLAG_ACTIVITY_CLEAR_TOP
If set, and the activity being launched is already running in the current task, then instead of launching a new instance of that activity, all of the other activities on top of it will be closed and this Intent will be delivered to the (now on top) old activity as a new Intent.
EDIT: this is a good resource to read, if you haven't did it yet:
Tasks and Back Stack.
Yes, you can do that. You simply code an intent for activity a to the button.
Use the command
finish():
You will be reverted to the main page
or else write an intent pointing to a
You can send information to different Activities via Intents.
Intent myIntent = new Intent(this, AvitivityName.class);
startActivity(myIntent);
Don't forget to add your Activities in AndroidManifest.xml.
Here's some tutorial on Android Intents:
how to use Android intents.
how to switch to another activity with a button click.
I am new in android and I have total 6-7 activities in my application. I want to know how can I manage my activities properly means when I move to the A->B->C->D like that. Then how can I move that the stack of these activities not created.
On moving from one activity to the other I am using the below code:
Intent intent=new Intent(current.this,next.class);
startActivityForResult(intent, 0);
And now if I want to move back on the earlier activity I used the code as:
Intent start = new Intent(current.this,next.class);
startActivity(start);
finishActivity(0);
Is there a special reason that you don't want to use the activity stack and let the activities handle themselves?
The Android system has done a very good job with the activity lifecycle. It allows you to start an Activity from different places without confusing the user because the back button will bring the user back to a different activity.
If you don't have a very good reason to not use the Android guideline try to stick to the way the system is doing it. Every other thing will only give you problems.
You are starting activities for a result but how I understand you you will never return to them.
You can start an Activity and after that just finish the current Activity. That way the activity will not be put on the back stack. Now you need to listen for back button pushes and create the activities that you want to bring the user to.
If you want to move from Activity A to D like going to the start/home screen of you app you do the following:
Intent goBackToA = new Intent(context, StdActivity.class);
goBackToA.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
startActivity(goBackToA);
The flag FLAG_ACTIVITY_CLEAR_TOP will tell the system that if the backstack contains an instance of the Activity this activity will be shown and all activity that are between the current activity and the target activity are removed from the backstack. This allows you to go back to a home activity without creating huge loops that the user can move through with the back button.
To move back to the previous activity you don't have to create a new intent, you can simply call this.finish() on the one that should dissapear.
To move back to the previous activity you don't have to create a new intent, you can simply call this.finish() on the one that should dissapeear or you can press Back button to see the previous Activity .
whenever you want to navigate from one class to another use this code, may be this help you to navigate the Activity,
Intent nextpage = new Intent(CurrentActivity.this,NextActivity.class);
startActivity(nextpage);
this.finish();