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Subclassing CompoundButton to create a three states checkbox

I'm new to android dev and I like to make a 3 states checkbox for my app. How is that possible ?
It should allow the user to switch between checked/unchecked/misc states.
I'm a bit lost. Should I subclasses CompoundButton and modify the state-list drawable ? I'm actually stuck at subclassing.

I was once looking for the same thing and found this. I ended up changing my requirements so cannot speak to its effectiveness, but looks like they implement the entire thing as Button, see ThreeStateButton and ThreeStateCheckBox.

Android Custom Buttons: Alternative to Multiple Graphics?

I think all custom button tutorials I have been able to find for Android assume you are using three images for your button: a normal image, a pressed image, and a focused image.
Instead of essentially tripling the size of a given button's resources (and creating more work for the artist/UX guy), is it possible to only supply a normal button image, and for the other states, draw some sort of overlay over the existing button by extending the Button class?
Has anybody tried doing this with any success, or is it just accepted that all custom buttons need an image for each state and that is that?

You could by overriding the draw methods of the view in your custom button but it would be a simple process as you would have to also identify the different states yourself.

I think the correct answer to this question is essentially what #Luksprog said in the comments... It simply isn't worth it. Just make the extra art.

Make a toggle button to widget

How do I add a button to a widget, not for opening an activity or something?
Just for toggling for example Wi-Fi :) Could it be done by a ImageButton or something like that? I just can't figure out how to add an onClickListener.

I have updated my answer now that I understand you are trying to write an AppWidget.
AppWidgets support only a limited set of Views and ToggleButton is not one of them. The list of Views supported by AppWidgets can be found here:
http://developer.android.com/guide/topics/appwidgets/index.html#CreatingLayout
You will have to use an ImageButton and remember its toggled state yourself. You can set it's image source to a different image depending on whether it is toggled or not. See ImageButton for more info:
http://developer.android.com/reference/android/widget/ImageButton.html

How to highlight clicks in app widget?

I have an app widget which runs neatly. However, I am unable to highlight a click on a linked item. I've seen it in the standard app widgets like 'Music' and 'Power Control', for instance. Moreover, I've also been studying the Music app widget's source at album_appwidget.xml. The only thing I could think of is the LinearLayout defined at lines 23-35 which states
android:clickable="true"
Unfortunately, this does not work for me. So does anyone have a hint on how to highlight a click on an app widget? I've tried the LinearLayout, TextView and Button. None of them displayed a border as a highlight.
Thanks in advance,
Steff

you need to create images for those states like focussed state, pressed etc like in a button and define them in your background.
Try looking at the custom buttons where its explained how to accomplish the task thats similar to your needs.
http://www.gersic.com/blog.php?id=56.
if you want to look more and add more states you may ge better idea if you look at the android source code for buttons where they have images for each state of the button and every other widget.

Android button bar toggle

I am looking for a UI view that imitates the functionality of the
Google Maps directions screen UI control where it allows the user to
pick the type of directions allowed, either Car, Transit or Walking.
Like this --> http://snapplr.com/50rh
The widget is essentially three buttons laid out horizontally with
rounded corners only on the left of the first and right of the thirdbutton.
I can't see a standard way to do this, although it seems like it would
be a common widget. Is there some other standard way of presenting a
multi-choice grouping in a horizontal layout as a "single" layout
object.

I am not aware of a button bar widget in the Android SDK. You would create one with ImageButtons in a LinearLayout, with custom backgrounds for all (to give the gloss-black look, to handle the varied sets of corners, and to handle the selected vs. not imagery). You would then need to add the toggling smarts, such that pushing one makes it selected and makes the others in the layout not selected.
If you wish to stick to simpler existing widgets, Spinner, RadioButton, or ToggleButton would be the most likely candidates.

I don't think there is a built-in way to do it. I can think of two ways to accomplish it. The first would be to create a custom style for the TabWidget. The second would be to create your own custom widget. Making a TabWidget style might be more flexible because you could easily come back and add or remove tabs and it would update accordingly. Making your own custom widget would give you much more control over how the widget looks and acts. So really you need to see what would be the best fit for what you're trying to do.

Best button bar I've found: http://androidworkz.com/2011/02/04/custom-menu-bar-tabs-how-to-hook-the-menu-button-to-showhide-a-custom-tab-bar/
It's thought to be used as a replacement for the menu, but I believe it's also great for a custom button bar. I'm actually gonna integrate it in my app straight away :-)
Kudos for androidworkz, the original author.

I think the power control widget does what you want. Looking at the source for the widget, it uses a combination of LinearLayouts & ImageViews to achieve the layout.
Layout file: https://android.googlesource.com/platform/packages/apps/Settings/+/froyo-release/res/layout/widget.xml
Source code: https://android.googlesource.com/platform/packages/apps/Settings/+/froyo-release/src/com/android/settings/widget/SettingsAppWidgetProvider.java