CWAC MergeAdapter: Stitching Together Rows

MergeAdapter accepts a mix of Adapters and Views and presents them as one contiguous whole to whatever ListView it is poured into. This is good for cases where you have multiple data sources, or if you have a handful of ordinary Views to mix in with lists of data, or the like.

Simply create a MergeAdapter and call addAdapter(), addView(), or addViews() (latter accepting a List<View>), then attach your adapter to the ListView.

There is also MergeSpinnerAdapter for use with Spinner widgets.

This is packaged as an Android library project, though a simple JAR is also available.

Usage

You can use MergeAdapter directly or subclass it. The latter is needed to support controlling which rows are/are not enabled.

Constructors

There is only one, no-argument constructor at this time. Just call new MergeAdapter() or new MergeSpinnerAdapter() and you are on your way!

Adding Content

You have three methods for defining what goes into the MergeAdapter. You can call addAdapter() to have all of that adapter's rows appear in the combined roster. You can call addView() to add a single View as a row. You can also call addViews() to add a List of View objects to use as rows.

NOTE: MergeSpinnerAdapter only supports addAdapter().

Each of these will appear in combined roster in the order they were added.

The addView() and addViews() methods have a variant that accepts a boolean 2nd parameter. Set this boolean to true if you want the rows represented by these views to be enabled (i.e., selectable). The default is that they are disabled, for use as if they were header rows. For adapters added via addAdapter(), the determination of whether or not rows are enabled is determined by the underlying adapter.

Other Methods to Override

You are welcome to override other methods as well, since this is just an Adapter.

Supporting isEnabled()

If you wish, your adapters wrapped by MergeAdapter can override isEnabled(), and MergeAdapter should enable and disable the rows as directed.

Timing

You must pour the contents into the MergeAdapter before calling setListAdapter() to associate the MergeAdapter with a ListView. This limitation is required because Android only calls getViewTypeCount() once, and adding more views or adapters adds more view types.

Note, though, that you can modify the underlying adapters. So, for example, if you add a CursorAdapter to the MergeAdapter, and you requery() the Cursor, the changes should be reflected via the MergeAdapter to whatever AdapterView the MergeAdapter is connected to.

Supporting android:id/empty

A ListActivity supports a widget in its layout, with an android:id of @android:id/empty, which will be displayed if the list is empty. More specifically, it will be displayed if the MergeAdapter returns true for isEmpty(). The default implementation of isEmpty() in BaseAdapter checks getCount() and compares it to 0.

In many cases, this default will be fine. However, if you are adding regular Views to the adapter (e.g., section headings), then getCount() will include these additional rows, and so isEmpty() will never return true. In this case, you may need to override isEmpty() to implement your own business logic to determine when the list is, indeed, "empty".

Contents of MergeSpinnerAdapter

You should add properly-configured SpinnerAdapter implementations (e.g., ArrayAdapter, CursorAdapter) to a MergeSpinnerAdapter to have it work properly.

Active/Inactive Contents

By default, everything that you add to the MergeAdapter is "active" and contributes to the resulting compound contents. However, you can call setActive() to toggle whether some piece is active or inactive. Inactive pieces do not contribute to the contents, removing them entirely from the ListView (or wherever you are using this).

There are two flavors of setActive(). Both take a boolean second parameter, with true meaning the piece is active and false for inactive. The first parameter is either a ListAdapter that you added already or a View that you added already (individually or as part of a List).

Dependencies

This project requires the CWAC SackOfViewsAdapter. A copy of a compatible JAR can be found in the libs/ directory of the project, though you are welcome to try newer ones, or ones that you have patched yourself.

This project should work on API Level 4 and higher, except for any portions that may be noted otherwise in this document. Please report bugs if you find features that do not work on API Level 4 and are not noted as requiring a higher version.

Version

This is version v0.4.0 of this module, meaning it is downright respectable.

For those of you updating from a previous version, please note that you need a new edition of the SackOfViewsAdapter JAR as well.

Demo

In the demo/ sub-project you will find a sample activity that demonstrates the use of MergeAdapter.

Note that when you build the JAR via ant jar, the sample activity is not included, nor any resources -- only the compiled classes for the actual library are put into the JAR.

License

The code in this project is licensed under the Apache Software License 2.0, per the terms of the included LICENSE file.

Questions

If you have questions regarding the use of this code, please post a question on StackOverflow tagged with commonsware and android. Be sure to indicate what CWAC module you are having issues with, and be sure to include source code and stack traces if you are encountering crashes.

If you have encountered what is clearly a bug, please post an issue. Be certain to include complete steps for reproducing the issue.

Do not ask for help via Twitter.

Release Notes

• v0.4.0: added setActive()
• v0.3.1: added workaround for http://code.google.com/p/android/issues/detail?id=16155
• v0.3.0: added MergeSpinnerAdapter support
• v0.2.1: added getAdapter() method to return the ListAdapter associated with a given position
• v0.2.0: converted to Android library project, added enabled versions of addView() and addViews(), correctly cascades data set changes from underlying adapters

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