How to perform validation before new tab is selected or swiping to a new fragment with Swipe Tabs in Android?

Question

I Have 4 tabs. But before allowing the user to move on to the other tab using Swiping or tab pressing, I want to perform all validations relating to the fragment attached with the current tab. How can I achieve that?

Now that Action Bar Tab Listener is deprecated, what are methods can be used to do this?

Answer 1

One way of doing it is in your TabsPagerAdapter, in your getItemPosition method.

@Override
public int getItemPosition(Object object) {
    if (object instanceof ValidatedFragment) {
        ((ValidatedFragment) object).validate();
    }
    return super.getItemPosition(object);
}

Then you can define an interface for ValidateFragment

public interface ValidateFragment {
    public void validate();
}

And finally, your fragment can extend ValidateFragment and implement the validation:

YouFragment implements ValidateFragment {
....
@override
public void validate(){
    //Do your validation here
}
...

}

Another way you can do it, is by using the method setUserVisibleHint, that gets called everytime your fragment is visible:

 @Override
public void setUserVisibleHint(boolean isVisibleToUser) {
    super.setUserVisibleHint(isVisibleToUser);
    if (isVisibleToUser) {
        //Do your validation here
    }
}

Edit:
if you don't want the user to be able to swipe if the fragment is not validated, I think you should implement your own ViewPager class, and override onInterceptTouchEvent and onTouchEvent if the frags are not validated.

@Override
public boolean onInterceptTouchEvent(MotionEvent arg0) {
    //Validate here and return false if the user shouldn't be able to swipe
    return false;
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    //Validate here and return false if the user shouldn't be able to swipe
    return false;
}

Also, you can try to use the setOnTouchListener method of your ViewPager in your Activity, and add a similar logic to what your currently have on your Action Bar Tab Listener

mPager.setOnTouchListener(new OnTouchListener()
{           
    @Override
    public boolean onTouch(View v, MotionEvent event)
    {
        return true;
    }
});

This SO question will be usefull for implementing both options.