viewPager page change for android MVVM

Question

    <Button
        android:id="@+id/onboard_next_button"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textColor="@color/white"
        android:text="@string/next"
        android:onClick="@{vm::onButtonNext}"
        android:background="@color/customColor"
        android:layout_alignParentBottom="true"/>

I am implementing a viewpager page change logic on a button. Which is super easy if it was standard MVC. All I have to do is to write something like

 @Override
 public void onButtonNext(View view) {
    // viewPager does not exist in my onButtonNext function because this is the viewModel
   viewPager.setCurrentItem(viewPager.getCurrentItem() + 1, true);
 }

because viewPager instance exists in my fragment or activity.

However, because I am implementing this in MVVM, I have no access to viewPager. How do I implement a viewPager.setCurrentItem in my viewModel if I do not have access to viewPager instance?

Answer 1

However, because I am implementing this in MVVM, I have no access to viewPager. How do I implement a viewPager.setCurrentItem in my viewModel if I do not have access to viewPager instance?

you need a public static void method annotated with @BindingAdapter.

Eg

  @BindingAdapter("currentItem")
  public static void setCurrentItem(ViewPager viewPager, int item) {
  }

and in the layout with will use something like app:currentItem . Of course your VM has to provide the int property or a getter for the item. Android takes care of the rest. You can read more about BindingAdapter here