Textbox that can be undo (UNDO, redo) in multiple steps

 

The default textbox can only be undo in one step, and there is no redo operation (secondary Undo is equivalent to a redo operation ). The following component implements the multi-step Undo (undo and redo) operations of textbox. The code is adapted to Kevin. syntaxtextbox (the original code is the Undo and redo functions implemented for RichTextBox ). UsingSystem;UsingSystem. Collections. Generic;UsingSystem. Windows. forms;NamespaceEkinglong. Drawing. Forms {/// <Summary> /// textbox that can be undone in multiple steps /// </Summary> Public partial classTextboxex: textbox {// Undo/Redo members privateList <undoredoinfo> mundolist =NewList <undoredoinfo> ();PrivateStack <undoredoinfo> mredostack =NewStack <undoredoinfo> ();Private boolMisundo =False;PrivateUndoredoinfo mlastinfo =NewUndoredoinfo ("", 0 );Private intMmaxundoredosteps = 50;/// <Summary> // The on text changed overrided. // </Summary> // <Param name = "E"> </param> protected override voidOntextchanged (eventargs e ){Base. Ontextchanged (E );If(! Misundo) {mredostack. Clear (); mundolist. insert (0, mlastinfo );This. Limitundo (); mlastinfo =NewUndoredoinfo (text, selectionstart );}// Invalidate ();}/// <Summary> /// sets and obtains the maximum number of steps allowed by the Undo operation. // </Summary> Public intMaxundoredosteps {Set{Mmaxundoredosteps = value ;}Get{ReturnMmaxundoredosteps ;}}/// <Summary> /// clear undo and redo operation information /// </Summary> Public voidClearundoandredo () {mundolist. Clear (); mredostack. Clear ();}/// <Summary> /// determine whether undo operations can be performed /// </Summary> Public new boolCanundo {Get{ReturnMundolist. Count> 0 ;}}/// <Summary> /// determine whether redo operations can be performed. /// </Summary> Public boolCanredo {Get{ReturnMredostack. Count> 0 ;}}/// <Summary> /// undo the operation /// </Summary> Public new voidUndo (){If(! Canundo)Return; Misundo =True; Mredostack. Push (NewUndoredoinfo (text, selectionstart); undoredoinfo info = (undoredoinfo) mundolist [0]; mundolist. removeat (0); text = info. text; selectionstart = info. cursorlocation; scrolltocaret (); mlastinfo = Info; misundo =False;}/// <Summary> /// repeated operation /// </Summary> Public voidRedo (){If(! Canredo)Return; Misundo =True; Mundolist. insert (0,NewUndoredoinfo (text, selectionstart); limitundo (); undoredoinfo info = (undoredoinfo) mredostack. pop (); text = info. text; selectionstart = info. cursorlocation; scrolltocaret (); misundo =False;}Private voidLimitundo (){While(Mundolist. Count> mmaxundoredosteps) {mundolist. removeat (mmaxundoredosteps );}}Private classUndoredoinfo {PublicUndoredoinfo (StringText,IntCursorloc) {text = text; cursorlocation = cursorloc ;}Public readonly intCursorlocation;Public readonly stringText ;}}}

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