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什么是事务机制

首先，什么是事务机制。软件事务机制是指一种在软件系统中用于管理一系列操作的方法，这些操作要么全部成功完成，要么全部失败，不会出现部分完成的情况。事务机制确保了数据的一致性和完整性，特别是在并发操作和系统故障的情况下。以下是软件事务机制的一些关键特征：
原子性（Atomicity）：事务中的所有操作要么全部完成，要么全部不发生。如果事务中的任何一个操作失败，整个事务都会回滚到开始前的状态。
一致性（Consistency）：事务必须使数据库从一个一致性状态转移到另一个一致性状态。在事务开始和结束时，数据库的数据完整性约束必须保持不变。
隔离性（Isolation）：并发执行的事务彼此之间应该是隔离的，一个事务的执行不应该被其他事务干扰。这防止了事务之间的交互导致数据不一致。
持久性（Durability）：一旦事务提交，它对系统的影响应该是永久性的。即使发生系统故障，事务的结果也应该被保留。

Revit 的事务 Transaction

从官方文档中可以看到 Revit 和事务相关的类为 Transaction，这个类的关键接口有 Start、Commit 和 Rollback。

在 Revit 中是需要显式得调用 Start，然后在操作完成后进行 Commit，或者操作失败后调用 Rollback。
官方例子：

public void CreatingSketch(UIApplication uiApplication)
{Autodesk.Revit.DB.Document document = uiApplication.ActiveUIDocument.Document;Autodesk.Revit.ApplicationServices.Application application = uiApplication.Application;// Create a few geometry lines. These lines are transaction (not in the model),// therefore they do not need to be created inside a document transaction.XYZ Point1 = XYZ.Zero;XYZ Point2 = new XYZ(10, 0, 0);XYZ Point3 = new XYZ(10, 10, 0);XYZ Point4 = new XYZ(0, 10, 0);Line geomLine1 = Line.CreateBound(Point1, Point2);Line geomLine2 = Line.CreateBound(Point4, Point3);Line geomLine3 = Line.CreateBound(Point1, Point4);// This geometry plane is also transaction and does not need a transactionXYZ origin = XYZ.Zero;XYZ normal = new XYZ(0, 0, 1);Plane geomPlane = Plane.CreateByNormalAndOrigin(normal, origin);// In order to a sketch plane with model curves in it, we need// to start a transaction because such operations modify the model.// All and any transaction should be enclosed in a 'using'// block or guarded within a try-catch-finally blocks// to guarantee that a transaction does not out-live its scope.using (Transaction transaction = new Transaction(document)){if (transaction.Start("Create model curves") == TransactionStatus.Started){// Create a sketch plane in current documentSketchPlane sketch = SketchPlane.Create(document,geomPlane);// Create a ModelLine elements using the geometry lines and sketch planeModelLine line1 = document.Create.NewModelCurve(geomLine1, sketch) as ModelLine;ModelLine line2 = document.Create.NewModelCurve(geomLine2, sketch) as ModelLine;ModelLine line3 = document.Create.NewModelCurve(geomLine3, sketch) as ModelLine;// Ask the end user whether the changes are to be committed or notTaskDialog taskDialog = new TaskDialog("Revit");taskDialog.MainContent = "Click either [OK] to Commit, or [Cancel] to Roll back the transaction.";TaskDialogCommonButtons buttons = TaskDialogCommonButtons.Ok | TaskDialogCommonButtons.Cancel;taskDialog.CommonButtons = buttons;if (TaskDialogResult.Ok == taskDialog.Show()){// For many various reasons, a transaction may not be committed// if the changes made during the transaction do not result a valid model.// If committing a transaction fails or is canceled by the end user,// the resulting status would be RolledBack instead of Committed.if (TransactionStatus.Committed != transaction.Commit()){TaskDialog.Show("Failure", "Transaction could not be committed");}}else{transaction.RollBack();}}}
}

Revit 事务机制可能的实现

大型软件的实现肯定是非常复杂的，所以这里只是一个猜测。实际情况和下面的肯定存在巨大差异。
为了支持Undo和Redo功能，我们需要在Transaction类中添加一些额外的逻辑来记录操作的历史，并在需要时回滚或重做这些操作。以下是一个简化的C#实现，其中包含了基本的Undo和Redo功能：

using System;
using System.Collections.Generic;
public class Transaction
{private bool isStarted;private Stack<Action> undoStack;private Stack<Action> redoStack;public Transaction(){undoStack = new Stack<Action>();redoStack = new Stack<Action>();}public void Start(string transactionName){if (isStarted)throw new InvalidOperationException("Transaction has already started.");isStarted = true;Console.WriteLine($"Transaction '{transactionName}' started.");}public void Commit(){if (!isStarted)throw new InvalidOperationException("No transaction has been started.");isStarted = false;redoStack.Clear(); // Clear the redo stack because a new commit creates a new point of no returnConsole.WriteLine("Transaction committed.");}public void Rollback(){if (!isStarted)throw new InvalidOperationException("No transaction has been started.");while (undoStack.Count > 0){undoStack.Pop().Invoke(); // Execute all undo actions}isStarted = false;Console.WriteLine("Transaction rolled back.");}public void AddAction(Action action, Action undoAction){if (!isStarted)throw new InvalidOperationException("No transaction has been started. Start a transaction before adding actions.");undoStack.Push(undoAction); // Push the undo action onto the stackaction.Invoke(); // Execute the action}public void Undo(){if (undoStack.Count == 0)throw new InvalidOperationException("No actions to undo.");Action undoAction = undoStack.Pop();undoAction.Invoke(); // Execute the undo actionredoStack.Push(() => undoAction); // Push the inverse action onto the redo stack}public void Redo(){if (redoStack.Count == 0)throw new InvalidOperationException("No actions to redo.");Action redoAction = redoStack.Pop();redoAction.Invoke(); // Execute the redo actionundoStack.Push(() => redoAction); // Push the inverse action onto the undo stack}
}
// Example usage:
class Program
{static void Main(string[] args){Transaction transaction = new Transaction();transaction.Start("Sample Transaction");// Add actions with corresponding undo actionstransaction.AddAction(() => Console.WriteLine("Action 1 performed."),() => Console.WriteLine("Action 1 undone."));transaction.AddAction(() => Console.WriteLine("Action 2 performed."),() => Console.WriteLine("Action 2 undone."));// Commit the transactiontransaction.Commit();// Undo the last actiontransaction.Undo();// Redo the last actiontransaction.Redo();// Rollback the transaction (undo all actions)transaction.Rollback();}

}
在这个例子中，Transaction类有两个栈：undoStack用于存储撤销操作，redoStack用于存储重做操作。每个操作都有一个对应的撤销操作，它们一起被添加到事务中。
AddAction方法用于添加操作和对应的撤销操作到事务中。Undo和Redo方法用于执行撤销和重做操作，并相应地更新栈。
在Main方法中，我们创建了一个Transaction实例，并添加了两个操作。然后我们提交事务，执行撤销和重做操作，并最后回滚事务。
请注意，这个示例是为了演示目的而简化的。在实际应用中，操作可能涉及更复杂的状态管理，并且需要处理并发和异常情况。此外，撤销和重做操作可能需要更精细的控制，例如操作特定的对象属性或恢复到特定的状态。

**注：**思想来源于博主，部分内容来自AI