Change AppBarLayout height programmatically in Android

Question

I'm trying to implement Flexible Space with image pattern, using this tutorial.

Everything works fine.

Notice the height definition of the AppBarLayout which is 192dp.

I'd like to make the height 1/3 of the screen instead, to match this google example for the pattern here.

Here's the code in the activity's onCreate (the layout xml is exactly the same as in the tutorial):

AppBarLayout appbar = (AppBarLayout)findViewById(R.id.appbar);
float density = getResources().getDisplayMetrics().density;
float heightDp = getResources().getDisplayMetrics().heightPixels / density;
appbar.setLayoutParams(new CoordinatorLayout.LayoutParams(LayoutParams.MATCH_PARENT, Math.round(heightDp / 3)));

But for some reason, the result is not what I'm expecting. I can't see the app bar at all with this code. (without the code, the height shows as expected but it's from XML and can't be set dynamically).

Answer 1

Do this instead:

    AppBarLayout appbar = (AppBarLayout) findViewById(R.id.appbar);
    float heightDp = getResources().getDisplayMetrics().heightPixels / 3;
    CoordinatorLayout.LayoutParams lp = (CoordinatorLayout.LayoutParams)appbar.getLayoutParams();
    lp.height = (int)heightDp;

In your original code I think that you calculation for 1/3 of the screen was wrong, but you still should have seen something. It could be that the LayoutParams.MATCH_PARENT in the setLP() wasn't imported correctly. Always declare the view type first, i.e. CoordinatorLayout.LayoutParams just to make sure. Otherwise it can be easy to use a Framelayout.LayoutParams, for instance.

Answer 2

Some methods for changing the AppBarLayout height programatically with dividing, percent or by weight of the screen height:

private AppBarLayout appbar;

/**
 * @return AppBarLayout
 */
@Nullable
protected AppBarLayout getAppBar() {
    if (appbar == null) appbar = (AppBarLayout) findViewById(R.id.appbar);
    return appbar;
}

/**
 * @param divide Set AppBar height to screen height divided by 2->5
 */
protected void setAppBarLayoutHeightOfScreenDivide(@IntRange(from = 2, to = 5) int divide) {
    setAppBarLayoutHeightOfScreenPercent(100 / divide);
}

/**
 * @param percent Set AppBar height to 20->50% of screen height
 */
protected void setAppBarLayoutHeightOfScreenPercent(@IntRange(from = 20, to = 50) int percent) {
    setAppBarLayoutHeightOfScreenWeight(percent / 100F);
}

/**
 * @param weight Set AppBar height to 0.2->0.5 weight of screen height
 */
protected void setAppBarLayoutHeightOfScreenWeight(@FloatRange(from = 0.2F, to = 0.5F) float weight) {
    if (getAppBar() != null) {
        ViewGroup.LayoutParams params = getAppBar().getLayoutParams();
        params.height = Math.round(getResources().getDisplayMetrics().heightPixels * weight);
        getAppBar().setLayoutParams(params);
    }
}

If you want to follow the material design guidelines the height should be equal to the default height plus content increment(s) https://www.google.com/design/spec/layout/structure.html#structure-app-bar