B4J Question Weird List Add problem

alwaysbusy

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Longtime User
This is probably me, but I just don't see it and it is driving me nuts:

Running this code:
B4X: 
    Dim files As List = File.ListFiles(File.Combine(File.DirApp, "VR/moviesR/"))
    For i = 0 To files.Size - 1
        files.Set(i, files.Get(i) & "$R")
    Next
    ' here a load files from another folder
    Dim filesT As List = File.ListFiles(File.Combine(File.DirApp, "VR/moviesT/"))
    For i = 0 To filesT.Size - 1
        ' and want to add them to the first one
        files.Add(filesT.Get(i) & "$T")   '<--- immidiately fails here with the error
    Next

B4X: 
Error occurred on line: 64 (Main)
java.lang.UnsupportedOperationException
    at java.base/java.util.AbstractList.add(AbstractList.java:153)
    at java.base/java.util.AbstractList.add(AbstractList.java:111)
    at anywheresoftware.b4a.objects.collections.List.Add(List.java:71)
    at b4j.example.main._appstart(main.java:166)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at anywheresoftware.b4a.shell.Shell.runMethod(Shell.java:632)
    at anywheresoftware.b4a.shell.Shell.raiseEventImpl(Shell.java:234)
    at anywheresoftware.b4a.shell.Shell.raiseEvent(Shell.java:167)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.base/java.lang.reflect.Method.invoke(Method.java:566)
    at anywheresoftware.b4a.BA.raiseEvent2(BA.java:91)
    at anywheresoftware.b4a.shell.ShellBA.raiseEvent2(ShellBA.java:98)
    at anywheresoftware.b4a.BA.raiseEvent(BA.java:78)
    at b4j.example.main.start(main.java:38)
    at javafx.graphics/com.sun.javafx.application.LauncherImpl.lambda$launchApplication1$9(LauncherImpl.java:846)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runAndWait$12(PlatformImpl.java:455)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$10(PlatformImpl.java:428)
    at java.base/java.security.AccessController.doPrivileged(Native Method)
    at javafx.graphics/com.sun.javafx.application.PlatformImpl.lambda$runLater$11(PlatformImpl.java:427)
    at javafx.graphics/com.sun.glass.ui.InvokeLaterDispatcher$Future.run(InvokeLaterDispatcher.java:96)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
    at javafx.graphics/com.sun.glass.ui.win.WinApplication.lambda$runLoop$3(WinApplication.java:174)
    at java.base/java.lang.Thread.run(Thread.java:834)

Is the List we get back from File.ListFiles somehow not a normal B4J list?

My workaround currently is using a third list, but I'm just wondering what could be wrong.
B4X: 
Dim files As List
    files.Initialize
    
    Dim filesR As List = File.ListFiles(File.Combine(File.DirApp, "VR/moviesR/"))
    For i = 0 To filesR.Size - 1
        files.Add(filesR.Get(i) & "$R")
    Next
    Dim filesT As List = File.ListFiles(File.Combine(File.DirApp, "VR/moviesT/"))
    For i = 0 To filesT.Size - 1
        files.Add(filesT.Get(i) & "$T")
    Next

Alwaysbusy
 
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josejad

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Licensed User
Longtime User
Hi:

Without knowing why the error is produced (and that's probably what you want to know, instead another solution), have you tried with:

AddAll (List As List)
Adds all elements in the specified collection to the end of the list.
Note that you can add an array directly.
Example:
List.AddAll(Array As String("value1", "value2"))
 
Upvote 0

DonManfred

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Licensed User
Longtime User
alwaysbusy said:
Dim files As List = File.ListFiles(File.Combine(File.DirApp, "VR/moviesR/")) For i = 0 To files.Size - 1 files.Set(i, files.Get(i) & "$R") Next
Click to expand...
File. ListFiles (Dir As String) As List
Returns a read only list with all the files and directories which are stored in the specified path.
An uninitialized list will be returned if the folder is not accessible.
Click to expand...
 
Upvote 0

alwaysbusy

Expert
Licensed User
Longtime User
Yes, I knew that thx, but it needed to add a suffix to each filename. AddAll did not work if I tried to do it to the list returned by listfiles. But now I know it is because it is read only. A .Set did work so it is not fully readonly and what I did not understand.

B4X: 
Dim filesR As List = File.ListFiles(File.Combine(File.DirApp, "VR/moviesR/"))
For i = 0 To filesR.Size - 1
    ' does work
    filesR.Set(i, filesR.Get(i) & "$R")
Next

Alwaysbusy
 
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