Android Tutorial Android home screen widgets tutorial - part I

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Basic4android v1.6 adds support for home screen widgets. This tutorial will explain how to implement your own home screen widgets (also named App Widgets).

It is important to understand that the widgets are created and managed in another process, different than the process that your application is running in. The home screen application is hosting your widgets.
This means that it is not possible to directly access the widgets views. Instead we are using a special object named RemoteViews which gives us indirect access to the widget views.

Widgets do not support all views types. The following views are supported:
- Button (default drawable)
- Label (ColorDrawable or GradientDrawable)
- Panel (ColorDrawable or GradientDrawable)
- ImageView
- ProgressBar (both modes)

All views support the Click event and no other event.

The widget layout and configuration must be defined with XML files. During compilation Basic4android reads the layout file created with the designer and generates the required XML files.

Each widget is tied to a Service module. Through this module the widget is created and updated.

Creating a widget - step by step guide

- Add a Service module. Note that the service module handling the widget is a standard service.
- Design the widget layout with the designer. First add a Panel and then add the other views to this Panel.
The widget layout will be made from this panel.
- Add code similar to the following code the service module:
B4X:
Sub Process_Globals
    Dim rv As RemoteViews
End Sub

Sub Service_Create
    rv = ConfigureHomeWidget("LayoutFile", "rv", 0, "Widget Name")
End Sub

Sub Service_Start (StartingIntent As Intent)
     RV.HandleWidgetEvents(StartingIntent)
    Sleep(0)
    Service.StopAutomaticForeground
End Sub

Sub rv_RequestUpdate
    rv.UpdateWidget
End Sub

Sub rv_Disabled
    StopService("")
End Sub

Sub Service_Destroy

End Sub
- Compile and run your application. Go to the home screen, long press on the screen and you will see your widget listed on the widgets list.

ConfigureHomeWidget is a special keyword. At runtime it creates the RemoteViews object from the layout and set the events. At compile time the compiler generates the required files based on the arguments of this keyword.
The four parameters are: layout file, event name, update interval and the widget name.
Event name sets the subs that will handle the RequestUpdate and Disabled events.
The widget can be configured to update itself automatically. The interval, measured in minutes, defines how often will the widget request to update itself. Set to 0 to disable automatic updates. Updating the widget too often will have a bad impact on the battery. The minimum value is 30 minutes.
Widget name - the name that will appear in the widgets list.

As these arguments are read by the compiler, only strings or numbers are accepted.

Events:
B4X:
Sub Service_Start (StartingIntent As Intent)
    If rv.HandleWidgetEvents(StartingIntent) Then Return
End Sub
The above code checks the Intent message that caused this service to start and is responsible for raising the events related to the widget. It returns true if an event was raised.
The widget raises two events. RequestUpdate is raised when the widget needs to update itself. It will fire after adding the widget to the screen, after the device has booted, based on the scheduled updating interval (if set) or after the application was updated.
The Disabled event is raised when the last instance of our widget is removed from the screen.

As mentioned above all views support the Click event. All that needs to be done in order to handle the click event of a button named Button1 is to add a sub named Button1_Click (the sub name should actually match the EventName property which is by default the same as the name).
For example if you want to show the main Activity when the user presses on Button1 you can use this code:
B4X:
Sub Button1_Click
StartActivity(Main)
End Sub
Modifying the widget:
It is not possible to directly access the widget views. Instead we need to use one of the RemoteView.Set methods.
If we want to change the text of a label named Label1 then we need to write the following code:
B4X:
rv.SetText("Label1", "This is the new text.")
'do more changes if needed
rv.UpdateWidget
After writing all the changes we call rv.UpdateWidget to send the updates to the widget.

A simple example is attached.
The example adds a simple widget. The widget doesn't do anything useful.
SS-2011.07.11-12.55.04.png


Second part of this tutorial: http://www.basic4ppc.com/forum/basi...oid-home-screen-widgets-tutorial-part-ii.html

Note that it is recommended to test widgets in Release mode (the widget will fail in debug mode when the process is started by the OS).
 

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Last edited:

Massimiliano

Member
Licensed User
Hi,
I'm having some problems with my widget app (sticky service) and the other app activities.

When i show a msgbox inside other activities (not the widget) sometime apps crashes without any message
If i remove the widget (so the service it's stopped) from home screen all seems to be ok.
I've read something about services and modal msgbox, but any help on how to show messages (eg. menu about box, exit application confirm....) would be appreciated

many thanks,
Massimiliano

b4a v5.02
 

imgsimonebiliato

Well-Known Member
Licensed User
Hello.. Is it possibile to catch every single view of the widget?
Like this code
B4X:
For Each v As View In Activity.GetAllViewsRecursive
...
Next
 

imgsimonebiliato

Well-Known Member
Licensed User
Hello,
how can I create automatically a widget, after the application installation?
 

Rusty

Well-Known Member
Licensed User
I've seen where you can now install application shortcuts on the home screen :) and would like to have my widget (once installed) automatically be put on the home screen.
Is there a way/method to do this?
Thanks,
Rusty
 

imgsimonebiliato

Well-Known Member
Licensed User
I've seen where you can now install application shortcuts on the home screen :) and would like to have my widget (once installed) automatically be put on the home screen.
Is there a way/method to do this?
Thanks,
Rusty

You can't.. See my post #188 and #189
 

Galaz

New Member
Licensed User
Hi all,
it is possibile to get value of text from widget ?
To sum up: I update widget and I would like to get value.
Do not ask me why I need this if first I update so I should know the value.
If is possibile please write me how. Thank you.
 

Galaz

New Member
Licensed User
I'm sorry but I don't understand. Which text?

Hello,
Thank you for trying to understand me.
I have some labels in widet that I update. In another activity I would like to get value of those labels. It is possible ? Thank you.
 

Martin Larsen

Active Member
Licensed User
Widgets do not support all views types. The following views are supported:
- Button (default drawable)
- Label (ColorDrawable or GradientDrawable)
- Panel (ColorDrawable or GradientDrawable)
- ImageView
- ProgressBar (both modes)

Does this still apply to newer versions of B4A?

What about very obvious views such as TextView and ListView?
 

Martin Larsen

Active Member
Licensed User
Oh bad :-(

Why such limitations? This means that B4A is not really suited for app widgets as you can only make the most simple kinds of widgets. I think it is a pity because you can make so much with B4A, but now I will have to go back to plain Java based Android for my next app.

Erel, any plans for the future?
 
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