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<!DOCTYPE html> <html> <head> <meta charset="utf-8"> <meta name="viewport" content="width=device-width, initial-scale=1"> <title>GoJS® UndoManager Class</title> <script src="../../assets/js/jquery.min.js"></script> <script src="../../assets/js/bootstrap.min.js"></script> <script src="../../assets/js/highlight.js"></script> <script src="../../assets/js/api.js"></script> <script src="../../assets/js/fuse.min.js"></script> <link href="../../assets/css/bootstrap.min.css" rel="stylesheet" >  <link href="../../assets/css/main.css" rel="stylesheet" type="text/css"/> <link href="../../assets/css/api.css" rel="stylesheet" type="text/css"/>  <link rel="stylesheet" href="../../assets/css/highlight.css" type="text/css" media="all" /> </head> <body>  <nav id="non-fixed-nav" class="navbar navbar-inverse navbar-top"> <div class="container-fluid"> <div class="navbar-header"> <div class="navheader-container"> <div class="navheader-collapse" data-toggle="collapse" data-target="#navbar"> <a id="toplogo" 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class="table-cell" id="apisearch" data-base="../"> <div class="title">Search API</div> <div class="field"> <label for="search-field" class="search-icon"></label> <input id="search-field" type="text" /> </div> <ul class="results"> <li class="state loading">Preparing search index...</li> <li class="state failure">The search index is not available</li> </ul> </div> <div class="table-cell" id="apisumm"> <input type="checkbox" id="showsumms" /> <label class="apisumms" for="showsumms">Show Summaries</label> </div> </div> </div>  <div id="header" class="fineprint"> <b>GoJS</b>® Diagramming Components<br/>version 1.8.36 for JavaScript/HTML<br/>by <a href="https://www.nwoods.com/">Northwoods Software®</a> </div>  <h2 class="classTitle"> Class UndoManager </h2>  <p class="classsummary"> UndoManager observes and records model and diagram changes in transactions and supports undo/redo operations. You will need to set the <a href="../symbols/UndoManager.html#isEnabled" class="linkProperty">isEnabled</a> property to true in order for users to perform an undo or a redo. <p> Typically an operation will call <a href="../symbols/UndoManager.html#startTransaction" class="linkMethod">startTransaction</a>, make some changes to the <a href="../symbols/Model.html" class="linkConstructor">Model</a> or <a href="../symbols/Diagram.html" class="linkConstructor">Diagram</a>, and then call <a href="../symbols/UndoManager.html#commitTransaction" class="linkMethod">commitTransaction</a>. Any <a href="../symbols/ChangedEvent.html" class="linkConstructor">ChangedEvent</a>s that occur will be recorded in a <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a> object. If for some reason you do not wish to complete the transaction successfully, you can call <a href="../symbols/UndoManager.html#rollbackTransaction" class="linkMethod">rollbackTransaction</a> instead of <a href="../symbols/UndoManager.html#commitTransaction" class="linkMethod">commitTransaction</a>. <p> The <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> property is a list of <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a>s. <a href="../symbols/UndoManager.html#commitTransaction" class="linkMethod">commitTransaction</a> will add the <a href="../symbols/UndoManager.html#currentTransaction" class="linkProperty">currentTransaction</a> to the <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> list. <a href="../symbols/UndoManager.html#rollbackTransaction" class="linkMethod">rollbackTransaction</a> will undo the changes remembered in the <a href="../symbols/UndoManager.html#currentTransaction" class="linkProperty">currentTransaction</a> and then discard it, without changing the <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a>. You can limit how many transactions are remembered in the history by setting <a href="../symbols/UndoManager.html#maxHistoryLength" class="linkProperty">maxHistoryLength</a>. <p> Transactions may be nested. Be sure to call either <a href="../symbols/UndoManager.html#commitTransaction" class="linkMethod">commitTransaction</a> or <a href="../symbols/UndoManager.html#rollbackTransaction" class="linkMethod">rollbackTransaction</a> for each call to <a href="../symbols/UndoManager.html#startTransaction" class="linkMethod">startTransaction</a>. Avoid repeated start-commit-start-commit calls as a result of a user's actions. Instead, start, make all changes, and then commit. <p> If you want to restore the diagram to the state before the latest complete transaction, call <a href="../symbols/UndoManager.html#undo" class="linkMethod">undo</a>. Call <a href="../symbols/UndoManager.html#redo" class="linkMethod">redo</a> to change the diagram to a later state. If after some number of undo's you start a transaction, all of the history after the current state is discarded, and a new transaction may be recorded. You cannot undo or redo during a transaction. <p> Initially each <a href="../symbols/Model.html" class="linkConstructor">Model</a> has its own UndoManager. UndoManagers may be shared by multiple Models by replacing the standard <a href="../symbols/Model.html#undoManager" class="linkProperty">Model.undoManager</a> created by the model constructor. <p> There are several informational properties: <ul> <li><a href="../symbols/UndoManager.html#isInTransaction" class="linkProperty">isInTransaction</a> is true when a top-level transaction has been started that has not yet been committed or rolled-back.</li> <li><a href="../symbols/UndoManager.html#currentTransaction" class="linkProperty">currentTransaction</a> holds the flattened list of all <a href="../symbols/ChangedEvent.html" class="linkConstructor">ChangedEvent</a>s that have happened within the current transaction.</li> <li><a href="../symbols/UndoManager.html#transactionLevel" class="linkProperty">transactionLevel</a> indicates the current depth of nesting.</li> <li><a href="../symbols/UndoManager.html#nestedTransactionNames" class="linkProperty">nestedTransactionNames</a> holds the stack of transaction names supplied to <a href="../symbols/UndoManager.html#startTransaction" class="linkMethod">startTransaction</a> calls.</li> <li><a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> holds only complete top-level transactions.</li> <li><a href="../symbols/UndoManager.html#isUndoingRedoing" class="linkProperty">isUndoingRedoing</a> is true during a call to <a href="../symbols/UndoManager.html#undo" class="linkMethod">undo</a> or <a href="../symbols/UndoManager.html#redo" class="linkMethod">redo</a>.</li> <li><a href="../symbols/UndoManager.html#historyIndex" class="linkProperty">historyIndex</a> indicates which <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a> in the <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> is the next to be "undone"; this is decremented by each undo and incremented by a redo.</li> <li><a href="../symbols/UndoManager.html#transactionToUndo" class="linkProperty">transactionToUndo</a> and <a href="../symbols/UndoManager.html#transactionToRedo" class="linkProperty">transactionToRedo</a> indicate which <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a> may be undone or redone next, if any.</li> <li><a href="../symbols/UndoManager.html#models" class="linkProperty">models</a> returns an iterator over all of the <a href="../symbols/Model.html" class="linkConstructor">Model</a>s that this UndoManager is handling.</li> </ul> </p>  <h2 id="constructor" class="summaryCaption"> Constructor <span class="nodetails"> Summary</span><span class="details"> Details</span></h2> <div class="table-responsive"> <table class="summaryTable table table-bordered table-condensed" summary="A summary of the constructor documented in the class UndoManager."> <thead> <tr> <th scope="col" class="name">Name</th> <th scope="col" class="description">Description</th> </tr> </thead> <tbody> <tr> <td class="name" > <div class="name"> UndoManager() </div> </td> <td class="description"> <div class="description"> <p><p>The constructor produces an empty UndoManager with no transaction history. </div> </td> </tr> </tbody> </table> </div>  <h2 class="summaryCaption">Properties<span class="nodetails"> Summary</span><span class="details"> Details</span></h2> <div class="table-responsive"> <table class="summaryTable table table-bordered table-condensed" summary="A summary of the properties documented in the class UndoManager."> <thead> <tr> <th scope="col" class="name">Name, Value Type</th> <th scope="col" class="description">Description</th> </tr> </thead> <tbody> <tr id="currentTransaction" > <td class="name"> <div class="name"> currentTransaction </div> <div class="attributes"> <span class="light">{<a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a>}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property returns the current <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a> for recording additional model change events.<span class="nodetails" id="xpropcurrentTransaction"><a class="morelink" onclick="hst('propcurrentTransaction')">More...</a></span> <span class="details" id="propcurrentTransaction"> This is initialized and augmented by <a href="../symbols/UndoManager.html#handleChanged" class="linkMethod">handleChanged</a> before it is added to <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> by a top-level call to <a href="../symbols/UndoManager.html#commitTransaction" class="linkMethod">commitTransaction</a>. The value will be null between transactions.</span> </div> </td> </tr> <tr id="history" > <td class="name"> <div class="name"> history </div> <div class="attributes"> <span class="light">{List.<Transaction>}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property returns the whole history, a list of all of the <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a>s, each representing a transaction with some number of <a href="../symbols/ChangedEvent.html" class="linkConstructor">ChangedEvent</a>s.<span class="nodetails" id="xprophistory"><a class="morelink" onclick="hst('prophistory')">More...</a></span> <span class="details" id="prophistory"> </span><div class="details" id="dprophistory"><p> You should not modify this List.</div> </div> </td> </tr> <tr id="historyIndex" > <td class="name"> <div class="name"> historyIndex </div> <div class="attributes"> <span class="light">{number}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property returns the index into <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> for the current undoable <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a>.<span class="nodetails" id="xprophistoryIndex"><a class="morelink" onclick="hst('prophistoryIndex')">More...</a></span> <span class="details" id="prophistoryIndex"> The value is -1 if there is no undoable <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a> to be undone.</span> </div> </td> </tr> <tr id="isEnabled" > <td class="name"> <div class="name"> isEnabled </div> <div class="attributes"> <span class="light">{boolean}</span> </div> </td> <td class="description"> <div class="description">  <p>Gets or sets whether this UndoManager records any changes.<span class="nodetails" id="xpropisEnabled"><a class="morelink" onclick="hst('propisEnabled')">More...</a></span> <span class="details" id="propisEnabled"> The default value is false -- you need to set this to true if you want the user to be able to undo or redo. </span><div class="details" id="dpropisEnabled"><p> You can temporarily turn off recording by setting <a href="../symbols/Diagram.html#skipsUndoManager" class="linkProperty">Diagram.skipsUndoManager</a> and <a href="../symbols/Model.html#skipsUndoManager" class="linkProperty">Model.skipsUndoManager</a> to true.</div> </div> </td> </tr> <tr id="isInTransaction" > <td class="name"> <div class="name"> isInTransaction </div> <div class="attributes"> <span class="light">{boolean}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property is true after the first call to <a href="../symbols/UndoManager.html#startTransaction" class="linkMethod">startTransaction</a> and before a corresponding call to <a href="../symbols/UndoManager.html#commitTransaction" class="linkMethod">commitTransaction</a> or <a href="../symbols/UndoManager.html#rollbackTransaction" class="linkMethod">rollbackTransaction</a>.<span class="nodetails" id="xpropisInTransaction"><a class="morelink" onclick="hst('propisInTransaction')">More...</a></span> <span class="details" id="propisInTransaction"> </span><div class="details" id="dpropisInTransaction"><p> During a transaction <a href="../symbols/UndoManager.html#canUndo" class="linkMethod">canUndo</a> and <a href="../symbols/UndoManager.html#canRedo" class="linkMethod">canRedo</a> will be false. <a href="../symbols/UndoManager.html#currentTransaction" class="linkProperty">currentTransaction</a> may be non-null if any <a href="../symbols/ChangedEvent.html" class="linkConstructor">ChangedEvent</a>s were recorded.</div> </div> </td> </tr> <tr id="isUndoingRedoing" > <td class="name"> <div class="name"> isUndoingRedoing </div> <div class="attributes"> <span class="light">{boolean}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property is true during a call to <a href="../symbols/UndoManager.html#undo" class="linkMethod">undo</a> or <a href="../symbols/UndoManager.html#redo" class="linkMethod">redo</a>. </div> </td> </tr> <tr id="maxHistoryLength" > <td class="name"> <div class="name"> maxHistoryLength </div> <div class="attributes"> <span class="light">{number}</span> </div> </td> <td class="description"> <div class="description">  <p>Gets or sets the maximum number of transactions that this undo manager will remember.<span class="nodetails" id="xpropmaxHistoryLength"><a class="morelink" onclick="hst('propmaxHistoryLength')">More...</a></span> <span class="details" id="propmaxHistoryLength"> When a transaction is committed and the number exceeds this value, the UndoManager will discard the oldest transaction(s). The initial value is 999. A negative value is treated as if there were no limit. </span><div class="details" id="dpropmaxHistoryLength"><p> This property is useful in helping limit the memory consumption of typical applications. But this does not limit the number of <a href="../symbols/ChangedEvent.html" class="linkConstructor">ChangedEvent</a>s that are recorded, because there may be an unlimited number of those within each <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a>. Decreasing this value will not necessarily remove any existing <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a>s if there currently exist more in <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> than the new value permits.</div> </div> </td> </tr> <tr id="models" > <td class="name"> <div class="name"> models </div> <div class="attributes"> <span class="light">{Iterator.<Model>}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property returns an iterator for all of the <a href="../symbols/Model.html" class="linkConstructor">Model</a>s that this UndoManager is handling.<span class="nodetails" id="xpropmodels"><a class="morelink" onclick="hst('propmodels')">More...</a></span> <span class="details" id="propmodels"></span> <div class="seealso">See also: <ul class="seealsolist"> <li><a href="../symbols/UndoManager.html#addModel" class="linkMethod">addModel</a></li> <li><a href="../symbols/UndoManager.html#removeModel" class="linkMethod">removeModel</a></li> </ul> </div> </div> </td> </tr> <tr id="nestedTransactionNames" > <td class="name"> <div class="name"> nestedTransactionNames </div> <div class="attributes"> <span class="light">{List.<string>}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property returns a stack of ongoing transaction names.<span class="nodetails" id="xpropnestedTransactionNames"><a class="morelink" onclick="hst('propnestedTransactionNames')">More...</a></span> <span class="details" id="propnestedTransactionNames"> The outermost transaction name will be the first item in the list. The last one will be the name of the most recent (nested) call to <a href="../symbols/UndoManager.html#startTransaction" class="linkMethod">startTransaction</a>. </span><div class="details" id="dpropnestedTransactionNames"><p> You should not modify this List.</div> </div> </td> </tr> <tr id="transactionLevel" > <td class="name"> <div class="name"> transactionLevel </div> <div class="attributes"> <span class="light">{number}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property returns the current transaction level.<span class="nodetails" id="xproptransactionLevel"><a class="morelink" onclick="hst('proptransactionLevel')">More...</a></span> <span class="details" id="proptransactionLevel"> The value is zero when there is no ongoing transaction. The initial value is zero. <a href="../symbols/UndoManager.html#startTransaction" class="linkMethod">startTransaction</a> will increment this value; <a href="../symbols/UndoManager.html#commitTransaction" class="linkMethod">commitTransaction</a> or <a href="../symbols/UndoManager.html#rollbackTransaction" class="linkMethod">rollbackTransaction</a> will decrement it. When this value is greater than zero, <a href="../symbols/UndoManager.html#canUndo" class="linkMethod">canUndo</a> and <a href="../symbols/UndoManager.html#canRedo" class="linkMethod">canRedo</a> will be false, because additional logically related model change events may occur.</span> </div> </td> </tr> <tr id="transactionToRedo" > <td class="name"> <div class="name"> transactionToRedo </div> <div class="attributes"> <span class="light">{<a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a>}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property returns the <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a> in the <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> to be redone next.<span class="nodetails" id="xproptransactionToRedo"><a class="morelink" onclick="hst('proptransactionToRedo')">More...</a></span> <span class="details" id="proptransactionToRedo"> The value may be null if the UndoManager is not ready to perform a redo.</span> <div class="seealso">See also: <ul class="seealsolist"> <li><a href="../symbols/UndoManager.html#transactionToUndo" class="linkProperty">transactionToUndo</a></li> </ul> </div> </div> </td> </tr> <tr id="transactionToUndo" > <td class="name"> <div class="name"> transactionToUndo </div> <div class="attributes"> <span class="light">{<a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a>}</span> </div> </td> <td class="description"> <div class="description">  <p>This read-only property returns the <a href="../symbols/Transaction.html" class="linkConstructor">Transaction</a> in the <a href="../symbols/UndoManager.html#history" class="linkProperty">history</a> to be undone next.<span class="nodetails" id="xproptransactionToUndo"><a class="morelink" onclick="hst('proptransactionToUndo')">More...</a></span> <span class="details" id="proptransactionToUndo"> The value may be null if the UndoManager is not ready to perform an undo.</span> <div class="seealso">See also: <ul class="seealsolist"> <li><a href="../symbols/UndoManager.html#transactionToRedo" class="linkProperty">transactionToRedo</a></li> </ul> </div> </div> </td> </tr> </tbody> </table> </div>  <h2 class="summaryCaption">Method <span class="nodetails"> Summary</span><span class="details"> Details</span></h2> <div class="table-responsive"> <table class="summaryTable table table-bordered table-condensed" summary="A summary of the methods documented in the class UndoManager."> <thead> <tr> <th scope="col" class="name">Name, Return Type</th> <th scope="col" class="description">Description</th> </tr> </thead> <tbody> <tr id="addModel"> <td class="name"> <div class="name"> addModel(model) </div> <div class="attributes"> </div> </td> <td class="description"> <div class="description"> <p><p>Make sure this UndoManager knows about a <a href="../symbols/Model.html" class="linkConstructor">Model</a> for which it may receive <a href="../symbols/ChangedEvent.html" class="linkConstructor">ChangedEvent</a>s when the given <a href="../symbols/Model.html" class="linkConstructor">Model</a> is changed.<span class="nodetails" id="xmethaddModel"><a class="morelink" onclick="hst('methaddModel')">More...</a></span> <span class="details" id="methaddModel"> The model will also receive notifications about transactions and undo or redo operations. </span><div class="details" id="dmethaddModel"><p> You should not call this method during a transaction.</div> </p><div class="seealso">See also: <ul class="seealsolist"> <li><a href="../symbols/UndoManager.html#models" class="linkProperty">models</a></li> <li><a href="../symbols/UndoManager.html#removeModel" class="linkMethod">removeModel</a></li> </ul></div> <dl class="detailList"> <dt