Android Question Undo and Redo for EditText

[Hedi]

Hello guys,

Is there is any way to Undo and Redo in EditText?

I search the forum and not find anything for android.


Thanks.

 

[Erel]

[B4X] [class] UndoManager

 

[Hedi]

When I run the app I get this error:

manager_addstate (java line: 42)
java.lang.NullPointerException: Attempt to invoke virtual method "byte[] anywheresoftware.b4a.randomaccessfile.B4XSerializator.ConvertObjectToBytes(java.lang.Object)" on a null object reference
    at hedigrand.lucidzone.manager._addstate(manager.java:42)
    at hedigrand.lucidzone.main._timersettings_tick(main.java:16588)
    at java.lang.reflect.Method.invoke(Native Method)
    at anywheresoftware.b4a.BA.raiseEvent2(BA.java:221)
    at anywheresoftware.b4a.objects.Timer$TickTack.run(Timer.java:105)
    at android.os.Handler.handleCallback(Handler.java:938)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loopOnce(Looper.java:210)
    at android.os.Looper.loop(Looper.java:299)
    at android.app.ActivityThread.main(ActivityThread.java:8250)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:556)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1045)

 

[Hedi]

When I run the app I get this error:

manager_addstate (java line: 42)
java.lang.NullPointerException: Attempt to invoke virtual method "byte[] anywheresoftware.b4a.randomaccessfile.B4XSerializator.ConvertObjectToBytes(java.lang.Object)" on a null object reference
    at hedigrand.lucidzone.manager._addstate(manager.java:42)
    at hedigrand.lucidzone.main._timersettings_tick(main.java:16588)
    at java.lang.reflect.Method.invoke(Native Method)
    at anywheresoftware.b4a.BA.raiseEvent2(BA.java:221)
    at anywheresoftware.b4a.objects.Timer$TickTack.run(Timer.java:105)
    at android.os.Handler.handleCallback(Handler.java:938)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loopOnce(Looper.java:210)
    at android.os.Looper.loop(Looper.java:299)
    at android.app.ActivityThread.main(ActivityThread.java:8250)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:556)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1045)

Fixed! I forgot to call:

manager1.Initialize(EditText1.Text)


Thank you Erel, I am proud of you.

 

[Erel]

Thank you Erel, I am proud of you.

I'm proud of you, that you found the mistake.

 

[Hedi]

Here is an example of how Undo and Redo action works in EditText, step by step:

First add this class:

Sub Class_Globals
    Private stack As List
    Private ser As B4XSerializator
    Private index As Int
    Private const MAX_STACK_SIZE As Int = 100
End Sub

Public Sub Initialize (InitialState As Object)
    stack.Initialize
    index = -1
    AddState(InitialState)
End Sub

Public Sub AddState (state As Object)
    Dim b() As Byte = ser.ConvertObjectToBytes(state)
    If DifferentThanPrevState(b) Then
        If index < stack.Size - 1 Then
            'this happens when a new state is added after one or more undo actions.
            For i = stack.Size - 1 To index + 1 Step - 1
                stack.RemoveAt(i)
            Next
        End If
        stack.Add(b)
        If stack.Size >= MAX_STACK_SIZE Then
            stack.RemoveAt(1) 'keep the initial state
        End If
        index = stack.Size - 1
    End If
    'Log($"Stack size: ${stack.Size}"$)
End Sub

Public Sub Undo As Object
    If index > 0 Then index = index - 1
    Return ser.ConvertBytesToObject(stack.Get(index))
End Sub

'Will return Null if there is no redo state available.
Public Sub Redo As Object
    If index < stack.Size - 1 Then
        index = index + 1
        Return ser.ConvertBytesToObject(stack.Get(index))
    End If
    Return Null
End Sub

Private Sub DifferentThanPrevState(b() As Byte) As Boolean
    If index = -1 Then Return True
    Dim prev() As Byte = stack.Get(index)
    Return Not(CompareArrays(prev, b))
End Sub

Private Sub CompareArrays(a1() As Byte, a2() As Byte) As Boolean
    If a1.Length <> a2.Length Then Return False
    For i = 0 To a1.Length - 1
        If a1(i) <>  a2(i) Then Return False
    Next
    Return True
End Sub

Dim manager1 As manager

manager1.Initialize(EditText1.Text)

Type UndoData (text As String, selStart As Int)

Sub GetState As UndoData
    Dim ud As UndoData
    ud.Initialize
   
    ud.Text = EditText1.Text
    ud.selStart = EditText1.SelectionStart
   
    Return ud
End Sub

Sub Timer1_Tick
   
    manager1.AddState(GetState) 'nothing will happen if the state is the same as the previous one
   
End Sub

Sub SetState (ud As UndoData)
   
    EditText1.Text = ud.text
    EditText1.SelectionStart = ud.selStart
   
End Sub

Private Sub UndoBtn_Click
       
    Dim ud As UndoData = manager1.Undo
    SetState(ud)
       
End Sub

Private Sub RedoBtn_Click
       
    Dim ud As UndoData = manager1.Redo
    SetState(ud)
       
End Sub