Android Question String cannot be cast to ...

[FERNANDO SILVEIRA]

Hello Guys,

I starded facing the following problem. Can anyone identify what am I doing wrong?

Error occurred on line: 53 (Main)
String cannot be cast to ...​

Line presenting the error:

  wWordEmpty.SubString2(0, wWordOK.Length - 1)     ' <=== ERROR LINE 53

Sub Activity_Create(FirstTime As Boolean)
    'Do not forget to load the layout file created with the visual designer. For example:
    Activity.LoadLayout("Main")
    Log("*** Lendo tabela inteira para lista ***")
    lstWords1 = File.ReadList(File.DirAssets, "tabpalavras.txt")
    lstWords2.Initialize
    lstWords2.AddAll(lstWords1)
    lstWords2=ShuffleList(lstWords2)
    Log("LIST2  after shuffle: " &lstWords2)
   
    Dim wLeft As Int
    Dim cd As ColorDrawable
    Dim wLetras As Int
    Dim bg As Bitmap

    wWordOK = lstWords2.Get(Rnd(0,lstWords2.Size - 1))
    wWordOK = wWordOK.trim
    wWordEmpty = "          "
    wWordEmpty.SubString2(0, wWordOK.Length - 1)     ' <=== ERROR LINE 53
    wWordShuffled = wWordOK
   
    Do While wWordShuffled = wWordOK
        wWordShuffled = ShuffleWord(wWordOK)
    Loop
   
    bg = LoadBitmapResize(File.DirAssets, wWordOK & ".jpg", ImageView1.Width, ImageView1.Height, True)
    ImageView1.SetBackgroundImage(bg).Gravity = Gravity.CENTER
   
    wLetras = wWordShuffled.Length
    wLeft = (100%y - (wLetras * 45dip)) / (wLetras + 2)
    cd.Initialize2(Colors.Black, 5dip, 3dip, Colors.Green)
    DrawWord(wWordEmpty, wLeft, 250dip, True)
   
    wLeft = (100%y - (wLetras * 45dip)) / (wLetras + 2)
    cd.Initialize2(Colors.Red, 5dip, 3dip, Colors.Yellow)
    DrawWord(wWordShuffled, wLeft, 400dip, False)
   
End Sub

Regards,
Fernando

 

[OliverA]

Are you sure you did not mean to say

wWordEmpty = wWordEmpty.SubString2(0, wWordOK.Length - 1)

SubString does not modify the existing string (Strings are immutable, more here: https://www.javatpoint.com/immutable-string), but returns a string that has a modified version of the original string.
On the other hand, that's interesting that a String.SubString2 method throws a class exception if it returns to nothing (the return is not captured by a variable). A B4A project from scratch does not have the same behavior. Looks like this only happens in Debug mode (for your attached project).
BTW, this line

       lblLetter(i).Text = word.SubString2(i, i+1)

in your DrawWord sub will be your next challenge.

 

[FERNANDO SILVEIRA]

Thank you, Oliver

As I can see I still have a long way to go understanding substring concept within B4A.

To fix the issue I replaced the bugged line below:

    wWordEmpty.SubString2(0, wWordOK.Length - 1)     ' <=== ERROR LINE 53

for this one and now it is working:

     wWordEmpty = RepeatString(" ", wWordOK.Length - 1)


Sub RepeatString(str As String, times As Int) As String
    Dim result As String = ""
    For i = 0 To times
        result = result & str
    Next
    Return result
End Sub

 

[OliverA]

Even though for your code the performance gain may be near null, you may want to look into/learn about StringBuilder (https://www.b4x.com/android/help/core.html#stringbuilder). With it your code would become:

Sub RepeatString(str As String, times As Int) As String
    Dim sb as StringBuilder
    sb.Initialize
    For i = 0 To times
        sb.Append(" ")
    Next
    Return sb.ToString
End Sub

 

[Mahares]

you may want to look into/learn about StringBuilder

I think your code should be this way:

Sub RepeatString(str As String, times As Int) As String
    Dim sb As StringBuilder
    sb.Initialize
    For i = 0 To times -1
        sb.Append(str)
    Next
    Return sb.ToString
End Sub
Log(RepeatString("OliverA", 6) )  'displays:  OliverAOliverAOliverAOliverAOliverAOliverA

 

[OliverA]

I think your code should be this way:

Yes it should. I was fixated on spaces...

 

[Mahares]

Yes it should. I was fixated on spaces...

It is not a big deal. I think you are a powerhouse. You are someone that joined the forum less than 2 years ago and knows so much. Mind boggling.