Set starting height of CollapsingToolbarLayout

Question

I want to be able to scroll on the ImageView inside the CollapsingToolbarLayout. So how that would be possible, and How to set a starting height of that Image view?

Answer 1

Actually AppBarLayout has special method to apply such offset:

final int setAppBarTopBottomOffset(CoordinatorLayout coordinatorLayout, AppBarLayout appBarLayout, int newOffset, int minOffset, int maxOffset)

Unfortunately it has package-private access level, but we can invoke it through such intermediate chain:

private void setAppBarOffset(int offsetPx){
    CoordinatorLayout.LayoutParams params = (CoordinatorLayout.LayoutParams) mAppBarLayout.getLayoutParams();
    AppBarLayout.Behavior behavior = (AppBarLayout.Behavior) params.getBehavior();
    behavior.onNestedPreScroll(mCoordinatorLayour, mAppBarLayout, null, 0, offsetPx, new int[]{0, 0});
}

One thing to be mentioned - this method should be called after mAppBarLayout is already prepared and measured. So the right way is to call it via view's post method.

mCoordinatorLayour = (CoordinatorLayout) findViewById(R.id.root_coordinator);
mAppBarLayout = (AppBarLayout) findViewById(R.id.app_bar_layout);

mAppBarLayout.post(new Runnable() {
    @Override
    public void run() {
        int heightPx = findViewById(R.id.iv_header).getHeight();
        setAppBarOffset(heightPx/2);
    }
});