如何将视图设置为不使用Java中的scrollview滚动

Question

is it possible to programmically force a View inside a ScrollView NOT to scroll?

Like the alphabetic titles in the contacts list. The 'A' bar doesn't scroll when the user scrolls through the list of all contacts whose first names start with 'A'. When the user scrolls till the end of 'A', 'B' bar simply scrolls up from the bottom of ScrollView, finally reaplacing 'A' at the top and staying there.

My description is kind of abstract, hope you understand.

Also thanks in advance.

Answer 1

The contacts list uses the ListView and not the ScrollView. One way I think it can be done is to have a fixed header at the top. You can change its content depending on what is being displayed on the screen.

Attach a OnScrollListener to ListView. You will get the view with the first visible position in onScroll. Then change the content of the header according to the content in the view.

You don't need to add a header in your ListView for the first section in your list as it will be already handled in your ScrollListener. Keep the style for the header rows and the view at the top the same and you will have the illusion for the fixed header.

Answer 2

As mentioned earlier you need a ListView. For an effect similar to that in the People app in Android 4+ I have used this excellent library (free and open source).

Answer 3

I think you need a combination of the "static text" approach with "section headers" within the ScrollView: the list should contain disabled/non-clickable items with the letters "A", "B", etc. When a section header scrolls above the top of the view, change the contents of the static TextView above the ScrollView to the contents of the header. Ie, when the "B" header item scrolls out of view, the TextView now contains "B".

Of course, the tough part will be detecting when a "section header" scrolls off the top, or comes into view when scrolling in the opposite direction.

For bonus points, use a "push up" Animation in the TextView when it's contents change to make it look like the list item is rolling into the TextView. (There is an example of this Animation in the API Demos app in the SDK in "...\\view\\Animation2.java").

UPDATE: after further review... here is some classes, etc. related towards making this work (it was a fun exercise for me!):

android.widget.AbsListView.OnScrollListener interface to see how to detect scrolling events. You'll need to keep track of the previous "top of view" position to determine which direction you are scrolling (to pick the slide-up or -down animation).

The Animation I listed above is not really what you want -- better off to look at the android.widget.TextSwitcher class and the push*.xml files in the SDK/android-X/data/res/anim directory.

You'll certainly need your own adapter subclass to inject section views into the list: getView(...) can set the row view's properties (bkgnd, text style, etc.) differently if the row is a section header or not. Re-use this code in your TextSwitcher view factory to populate the static TextView/Switcher above the list.

Have fun...!