Show and hide the ActionBar
This topic describes how to show and hide the ActionBar, which are implemented in the following examples.
- ActionBarControlGridViewActivity
- ActionBarControlListViewActivity
- ActionBarControlRecyclerViewActivity
- ActionBarControlScrollViewActivity
- ActionBarControlWebViewActivity
Using the basic callbacks
Suppose you've already checked the "Quick start" section,
you wouldn't know the meaning of the codes yet.
So at first, let's see how those codes work.
ObservableScrollViewCallbacks
In the quick start guide, you wrote the implementation of ObservableScrollViewCallbacks (following methods).
@Override
public void onScrollChanged(int scrollY, boolean firstScroll, boolean dragging) {
}
@Override
public void onDownMotionEvent() {
}
@Override
public void onUpOrCancelMotionEvent(ScrollState scrollState) {
}
These are the methods of ObservableScrollViewCallbacks interface and all the Observable*Views can handle this callbacks.
onScrollChanged callback
This is called when the scroll change events occurred.
This won't be called just after the view is laid out, so if you'd like to initialize the position of your views with this method, you should call this manually or invoke scroll as appropriate.
You would expect it to be called after onCreate,
but ListView (or other views) does not call back
scroll change event, so Observable*Views cannot
call this.
Therefore you should write like this:
onScrollChanged(mListView.getCurrentScrollY(), false, false);
I know it's a bad pattern to call the "callback" methods from us, they should be called by the library when they should be. However, we cannot improve this because this behavior depends on the view classes in the Android SDK.
onDownMotionEvent callback
This is called when the down motion events occur.
This can be useful if you'd like to know when the touch (or dragging) has begun.
onUpOrCancelMotionEvent callback
This is called when the dragging ended or canceled. This is useful when you move some views when the scroll ends: showing/hiding a view, sliding a view to the anchor point, etc.
How it works: ActionBar animation
As I explained in the quick start section, the main animation code is in the onUpOrCancelMotionEvent.
What we want to do is:
- to hide the ActionBar when we swipe up the view, because we want to see the contents.
- to show the ActionBar when we swipe down the view, because we want to tap a button on the ActionBar (it could be sharing the contents or going back to the former screen, for example).
Either way, we should get the direction of scrolling when the dragging ends.
onUpOrCancelMotionEvent callback has a ScrollState parameter. This parameter indicates the direction of the scroll, so we can write like this:
public void onUpOrCancelMotionEvent(ScrollState scrollState) {
if (scrollState == ScrollState.UP) {
// TODO show or hide the ActionBar
} else if (scrollState == ScrollState.DOWN) {
// TODO show or hide the ActionBar
}
}
When you move your finger from the bottom of the screen to the top (swiping up), the state will be ScrollState.UP. So we can write ActionBar#hide() in this condition.
And this event occurs every time you scroll the view, so if the ActionBar is already hidden, you don't have to hide it anymore.
Now you know how to handle the other direction.
Show the ActionBar when ScrollState.DOWN is passed to the callback.
ActionBar ab = getSupportActionBar();
if (scrollState == ScrollState.UP) {
if (ab.isShowing()) {
ab.hide();
}
} else if (scrollState == ScrollState.DOWN) {
if (!ab.isShowing()) {
ab.show();
}
}
Conclusion
If you'd like to animate the ActionBar, you should write animation codes in the onUpOrCancelMotionEvent callback.
Also, we used ObservableListView in the quick start, but in this pattern all types of Observable*Views have the same behavior, so you can write exactly the same.