B4J Question Creating own events (from library)?

[KMatle]

I did not find a satisfying source here which explains how to raise an event (like in many libs here e.g. Job.Done). I just want to raise an event in one of my libs to use in the calling (Main) app.

 

[Erel]

See the raising events section here: https://www.b4x.com/android/forum/threads/java-creating-libraries-for-basic4android.6810/#content

ControlsFX library source code is available here: https://www.b4x.com/android/forum/t...with-enhanced-designer-support.62488/#content

 

[KMatle]

Hm. Don't get it.

Could someone provide a simple example for raising a simple non-ui event from a library (target is that a sub is called)?

 

[Roycefer]

There are few different ways to do this. If you want to raise an event sub in the Main thread from a non-Main thread, your best bet is to call ba.raiseEventFromDifferentThread(). In this way, the target sub will be executed in the Main thread and can access UI elements and it doesn't matter from which thread it is being called. If you use this method correctly, developers who use your library will be able to use the Sender keyword in their event subs.

You can also use CallSubDelayed which is a member function of anywheresoftware.b4a.keywords.Common. This will follow the normal rules of CallSubDelayed usage. There is no access to the Sender keyword using this method.

If you want to directly call an event sub in a blocking fashion (perhaps you need the return value of the event sub before you continue to the next line) then you will want your event sub to execute in the same thread as that from which it is being called. In this case, I use straight-forward Java reflection to call the target sub.

Whichever path you take, make sure to use the @Events annotation. It will make life a lot easier for the users of your library.

 

[jmon]

He probably means in a normal b4j library and not a java one.

You can have a look at one of my b4j class https://www.b4x.com/android/forum/threads/jshellqueue.58315/

First you need to store the module that your library will call to raise the event. You also need to store the name of the event.

After that you just use CallSub or CallSubDelayed to call your event.

CallSub(Module, EventName & "_QueueFinished")

.

Also you can add

#event:QueueFinished

at the top of your library to tell the IDE of the names of your events and provide the autocomplete feature.

EDIT:I think the example of jShellQueue doesn't have the source code. Check out this library instead https://www.b4x.com/android/forum/threads/jwebimageview.62883/ which will be a good example.

 

[KMatle]

After that you just use CallSub or CallSubDelayed to call your event.

Nice one.

As I see you initialize with

iv1.Initialize(apWiv, Me, "iv")

handing over the parent object/module. A lot of examples do it like this.

How do I get the caller Module from the lib like other lib's do it without (like HttpUtils doesn't need to initialize it with "me")?

 

[Erel]

The callback module must be passed when raising events from B4X code.

The callback is passed to HttpJob.Initialize.

You can see the source code here: https://www.b4x.com/android/forum/threads/okhttputils2.62105/

 

[KMatle]

The callback is passed to HttpJob.Initialize

Grmpf... Sorry. There are some days you better don't start your pc...

 

[jmon]

You also need to add

#raisesSynchronousEvents:yourFunctionName

At the top of your library for all the functions calling events with CallSub.