CODEWITHSUNDEEP
androidandroid-viewpager
Klaxon
Klaxon

Reputation: 53

How to go directly to a specific fragment using ViewPager2

I am trying to create an app using Viewpager2 that allows scrolling between fragments similar to below image but WITHOUT the tablayout at the top.

enter image description here

So if you scroll left and right you would swtich between the fragments. Thats fine and dandy.

However my final app would have more than 5 tabs so i dont want the tab layout listed on top. Instead I would have a menu option that would let user choose which fragment to view.

I cannot figure out how to get the viewpager to go to a specific fragment directly (eg. from 2nd fragment to the 5th fragment), and when navigating between fragments I do not want a fragment to start from scratch if if was created already.

I am using FragmentStateAdapter with my ViewPager2. Should i be using another adapter for this? Any ideas woule be greatful.

Upvotes: 2

Views: 3540

Answers (2)

jetspiking
jetspiking

Reputation: 304

The easiest way to implement this feature is to define your ViewPager as static in your activity (so you can access it from anywhere in your application, including fragments). You can make it public, or you can make it private and create a getter for it.

private static ViewPager mViewPager; // This is the global variable 
public static ViewPager getViewPager() { return mViewpager; } // This is the getter

Now lets say we have an activity MainActivity which contains the ViewPager. Each fragment inside this ViewPager contains a button which should control the page (doesn't have to be in the ViewPager, could be anywhere as long as it has a reference to your Activity and that Activity is still running, so don't start another one).

ViewPager contains the method 

setCurrentItem(int item, boolean smoothScroll)

(smoothScroll is optional and is just for animation purposes)

Now you can do:

MainActivity.getViewPager().setCurrentItem(itemNr);

Or if you want a fancy scroll animation:

MainActivity.getViewPager().setCurrentItem(itemNr, true);

Now your second question / issue was that you mentioned you don't want fragments to get recreated. In that case I think it is better to use FragmentPagerAdapter, which maintains your fragments. You can call the following method to set a limit to these pages:

mViewPager.setOffscreenPageLimit(LauncherViewPageAdapter.NUMBER_OF_PAGES); //NUMBER_OF_PAGES was just a static constant in my LauncherViewPageAdapter class which extended ViewPageAdapter.

Note: Default this limit is 3, but you really don't have to worry about performance. I implemented 4 pages / fragments (widgets, tiles, app list, application settings) without any memory issues (even on older devices). Just don't put them full with bitmaps / heavy memory usage stuff.

I'm currently working on a launcher application which also uses ViewPager, so feel free to reply with a question about the ViewPager, since I solved the basic issues I had.

Upvotes: 5

ljk
ljk

Reputation: 1616

You can make use of setCurrentItem method of your ViewPager2. Just pass the index your wish to navigate to starting from 0. As for not wanting the fragments to start from scratch simply use setOffscreenPageLimit method of viewpager2 and set it to like 4 in case you have 5 pages so that all 5 pages stay in memory. It actually defeats the purpose of FragmentStateAdapter and ViewPager2 though.

Upvotes: 3

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