DISCLAIMER:
This tutorial is written without testing code. There may be bugs, but try to understand the process, not copy the code.
An intent is a way for different applications to communicate at run time. It can be used to pass messages between activities and make them do actions. Using it with startActivity targets the intent to an activity. Broadcast intents are broadcast to all activities, and any applications with an intent filter can listen for it and perform an action.
Explicit Intents: The target component (service or activity) is known. (For e.g. an intent to the browser)
Implicit Intents: The system will determine which activity is best to launch this intent. (For e.g. Share intents)
More information on intents:
Intents and Intent Filters | Android Developers
In this example we have two apps.
- The Provider, that contains the data we need
- The Requester, that will request the data via Intent
Step 1: Setup the Provider to be able to receive intents
This can be done in two ways:
1. Explicitly setting the component, and making it visible by setting exported=true
2. Defining your own intent filter
We will do the second way since it is more structured.
We set up an intent filter to trigger our activity in the Provider.
In the manifest editor add the following, for the Activity you want to trigger.
You can also use a service (use AddServiceText instead)
Step 2: Code the Provider to return the data
When using an Activity,
...so far so good...
however do you see the problem here?
no? come on think harder
How does the Providor know which app to send the data back to? The Intent by default has no information about the Calling package.
Again, there are two (simpler) ways to deal with this
1. Add information about the Requestor in the intent extras so we can call it back
2. Use StartActivityForResult. This allows you to get the calling package name, but infact you do not even need it. You can just return the result as an intent back to the Requestor Activity.
However, this is the point where you pause and think about what your apps need to do. Are they working silently in the background? Or do they show a dialog at some point?
For now, we go with the first option, and assume that the Requestor sends us an intent action in the extras.
So in SendSettings we do,
Make note of how the return intent is initialized with the Callback field from the original recevied intent.
3. Set up the Requester
As you may have noticed, the Requester needs to be set up in the same way except for some minor differences. First you set up the manifest, with a different intent filter:
4. Code the Requester to request the data/settings
This can be anywhere in your code, but if its settings you want to request, it will probably be in activity create or resume. The thing to note here is how we initialiaze the intent with the ACTION of the PROVIDER. And we send the CallBack i.e. the intent of the REQUESTER as the CALLBACK so the provider can send us back the data.
5. Code the Requester to accept the data
Again this code is very similar to the Provider except that it gets the data
Points to note:
While I dont consider intents to be very advanced, it can be quite overwhelming for newbies, so do your research.
There are many ways to do things and combinations of services/activities can make things complicated.
You can add permissions on your intent filters, this way Plugin apps need to have your permission in their manifest. This helps in *some* access control, mainly you can list all apps that can access your app/settings/data.
To see this in operation you can look at my apps that plugin to each other Cloudpipes and PhoneBackup.
If I get time I may write a sample otherwise not.
This tutorial is written without testing code. There may be bugs, but try to understand the process, not copy the code.
An intent is a way for different applications to communicate at run time. It can be used to pass messages between activities and make them do actions. Using it with startActivity targets the intent to an activity. Broadcast intents are broadcast to all activities, and any applications with an intent filter can listen for it and perform an action.
Explicit Intents: The target component (service or activity) is known. (For e.g. an intent to the browser)
Implicit Intents: The system will determine which activity is best to launch this intent. (For e.g. Share intents)
More information on intents:
Intents and Intent Filters | Android Developers
In this example we have two apps.
- The Provider, that contains the data we need
- The Requester, that will request the data via Intent
Step 1: Setup the Provider to be able to receive intents
This can be done in two ways:
1. Explicitly setting the component, and making it visible by setting exported=true
2. Defining your own intent filter
We will do the second way since it is more structured.
We set up an intent filter to trigger our activity in the Provider.
In the manifest editor add the following, for the Activity you want to trigger.
You can also use a service (use AddServiceText instead)
B4X:
AddActivityText(Main, <intent-filter>
<action android:name="com.maximussoft.myprovider.REQUEST" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>)Step 2: Code the Provider to return the data
When using an Activity,
B4X:
Sub Activity_Resume
Dim in as Intent
in = Activity.GetStartingIntent
If in <> null Then
If In.HasExtra("GetSettings") Then
SendSettings(in)
Activity.Finish
Return
End If
End If
End Sub...so far so good...
however do you see the problem here?
no? come on think harder
How does the Providor know which app to send the data back to? The Intent by default has no information about the Calling package.
Again, there are two (simpler) ways to deal with this
1. Add information about the Requestor in the intent extras so we can call it back
2. Use StartActivityForResult. This allows you to get the calling package name, but infact you do not even need it. You can just return the result as an intent back to the Requestor Activity.
However, this is the point where you pause and think about what your apps need to do. Are they working silently in the background? Or do they show a dialog at some point?
For now, we go with the first option, and assume that the Requestor sends us an intent action in the extras.
So in SendSettings we do,
B4X:
Sub SendSettings(in as Intent)
Dim returnIntent as Intent
returnIntent.Initialize(in.GetExtra("Callback"),"")
returnIntent.AddCategory("android.intent.category.DEFAULT")
returnIntent.PutExtra("Settings",someGlobalSettings)
returnIntent.PutExtra("Successful","True")
StartActivity(returnIntent) 'Or StartService(returnIntent)
End Sub3. Set up the Requester
As you may have noticed, the Requester needs to be set up in the same way except for some minor differences. First you set up the manifest, with a different intent filter:
B4X:
AddActivityText(Main, <intent-filter>
<action android:name="com.maximussoft.myrequestor.CALLBACK" />
<category android:name="android.intent.category.DEFAULT" />
</intent-filter>)4. Code the Requester to request the data/settings
This can be anywhere in your code, but if its settings you want to request, it will probably be in activity create or resume. The thing to note here is how we initialiaze the intent with the ACTION of the PROVIDER. And we send the CallBack i.e. the intent of the REQUESTER as the CALLBACK so the provider can send us back the data.
B4X:
Sub RequestSettings
Dim in as Intent
in.Initialize("com.maximussoft.myprovider.REQUEST","")
in.AddCategory("android.intent.category.DEFAULT")
in.PutExtra("Callback","com.maximussoft.myrequestor.CALLBACK")
in.PutExtra("GetSettings","True")
StartActivity(in) 'Or StartService(returnIntent)
End Sub5. Code the Requester to accept the data
Again this code is very similar to the Provider except that it gets the data
B4X:
Sub Activity_Resume
Dim in as Intent
in = Activity.GetStartingIntent
If in <> null Then
If In.HasExtra("Settings") Then
AcceptSettings 'Do something here with your settings
End If
End If
End SubPoints to note:
While I dont consider intents to be very advanced, it can be quite overwhelming for newbies, so do your research.
There are many ways to do things and combinations of services/activities can make things complicated.
You can add permissions on your intent filters, this way Plugin apps need to have your permission in their manifest. This helps in *some* access control, mainly you can list all apps that can access your app/settings/data.
To see this in operation you can look at my apps that plugin to each other Cloudpipes and PhoneBackup.
If I get time I may write a sample otherwise not.
) question: is there a way, in a Start Activity intent, to "abort" the intent after receiving data?
