Android Code Snippet Implementing a callback with inline Java

This is a template that you can use when implementing a callback with inline Java, whether it is an interface or abstract class, inside a B4A/B4J class, such as B4XMainPage.

#if Java
public static class MyNetworkCallback extends android.net.ConnectivityManager.NetworkCallback {
    private final BA ba;
    public MyNetworkCallback(B4AClass me) {
        this.ba = me.getBA();
    }
    @Override
        public void onAvailable(android.net.Network network) {
            super.onAvailable(network);
            ba.raiseEvent(this, "network_state", true, network);
        }
        @Override
        public void onUnavailable() {
            super.onUnavailable();
            ba.raiseEvent(this, "network_state", false, null);
        }
}
#End If

1. public static class ...

2. The constructor expects a B4AClass. This is the B4X class instance. It gets the "ba" object from this instance, which makes it simple to raise events.

3. Implement code. Use ba.raiseEvent or raiseEventFromUI. Remember that the event name must be lowercase and should include an underscore (to avoid obfuscation issues). If not sure then use ba.raiseEventFromUI.

4. Create a callback instance with JavaObject

Dim callback As JavaObject
callback.InitializeNewInstance(GetType(Me) & "$MyNetworkCallback", Array(Me)) '$ + class name. And pass Me to the constructor

5. Optional step - use Wait For to wait for the event:

 Wait For Network_State (Available As Boolean, Network As Object)

 

[jkhazraji]

Is the code specific to B4XPages? An example would be of real benefit.

 

[Daestrum]

probably worth noting if obfuscated the _ in the sub name is really important, otherwise Java can't find it.

 

[Erel]

Is the code specific to B4XPages? An example would be of real benefit.

The code should be added to a class module. It will work with non-B4XPages classes.

 

[vinpolins]

The code should be added to a class module. It will work with non-B4XPages classes.

Hi,

In this Post you said that Don't use Wait For, use instead another sub to handle an event there, then call a different sub with CallSubDelayed.
But here we use Wait For to wait for the event (step 5).

So should we use Wait For, or better use Sub Network_State separately?

 

[Erel]

This is really not the correct place for this question. Start a new thread instead.

And the context is very important, the issue with ArchiverPlus event is an edge case related to the event firing on a background thread. Always prefer Wait For if possible.