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DesignerTransaction Class

Provides a way to group a series of design-time actions to improve performance and enable most types of changes to be undone.

Namespace: System.ComponentModel.Design
Assembly: System (in system.dll)

public abstract class DesignerTransaction : IDisposable
public abstract class DesignerTransaction implements IDisposable
public abstract class DesignerTransaction implements IDisposable
Not applicable.

Transactions can track actions that can be undone later. Changes made during a transaction can be reversed by canceling a transaction, which automatically attempts to reverse each change by setting each changed property to its pre-change value. Transactions can also improve performance during a series of operations by deferring updates to the display until the completion of the transaction.

When a transaction is in progress, some components defer their processing until the transaction has completed by listening to the TransactionOpening and TransactionClosed events. The Properties window, for example, does not update its display after a transaction has opened until the transaction has closed.

To use transactions for reversible or multiple operations, have your designer create a DesignerTransaction for each operation or series of operations which should be reversible. Be careful not to perform actions outside the transactions that might prevent a sequence of undo events from completing successfully.

You can obtain a new DesignerTransaction by calling the CreateTransaction method of an IDesignerHost. Be sure to obtain each DesignerTransaction from the active IDesignerHost in order to correctly integrate with the designer transaction processing mechanism, rather than creating a new DesignerTransaction directly.

To perform an action within a transaction, you must first create a transaction. Then you must call the OnComponentChanging method before each change or set of changes occurs, and the OnComponentChanged method after each change or set of changes occur. Finally, complete and close the transaction by calling the Commit method.

NoteNote:

When making changes to property values, use the SetValue method of a PropertyDescriptor, which calls the component change methods of the IComponentChangeService and creates a DesignerTransaction representing the change automatically.

To perform a transaction, complete the following steps:

  1. Call CreateTransaction to obtain a DesignerTransaction that can be used to control the transaction.

  2. Within a try block, for each action that you want to track with a DesignerTransaction, call the OnComponentChanging method, make the change or changes, then call the OnComponentChanged method to signal that the change or changes have been made.

  3. To complete the transaction, call Commit from within a finally block.

In C#, you can use the using statement rather than a try/finally block, such as in the following example.

 using (host.CreateTransaction() {
 // Insert your code here.
 }

To cancel and attempt to roll back a transaction before it has been committed, call the Cancel method. When the Cancel method is invoked, the actions tracked by the DesignerTransaction are reversed to attempt to roll back the changes. To undo actions that occurred as part of earlier transactions, you must use the undo command provided by the development environment.

NoteNote:

The HostProtectionAttribute attribute applied to this class has the following Resources property value: SharedState. The HostProtectionAttribute does not affect desktop applications (which are typically started by double-clicking an icon, typing a command, or entering a URL in a browser). For more information, see the HostProtectionAttribute class or SQL Server Programming and Host Protection Attributes.

The following code example program demonstrates how to create a DesignerTransaction from a designer. To run this sample, compile the source code into a class library. You must add a reference to the System.Design assembly. In a new project, add a reference to the compiled DLL and add the component in the library to the Toolbox.

There is extensive support for this feature in Visual Studio.

Walkthrough: Automatically Populating the Toolbox with Custom Components
Walkthrough: Automatically Populating the Toolbox with Custom Components
Walkthrough: Automatically Populating the Toolbox with Custom Components
Walkthrough: Automatically Populating the Toolbox with Custom Components
Walkthrough: Automatically Populating the Toolbox with Custom Components

The designer can optionally display notifications about designer transaction events. If you add an instance of the DTComponent to a form while in design mode, a message box appears asking whether you would like to receive designer transaction event notifications. You may toggle these notifications using the shortcut menu that appears when you right-click an instance of the DTComponent. Transactions are created when you change values using the Properties window. You can also have the designer perform a transaction by clicking Perform Example Transaction on the shortcut menu for the component.

using System;
using System.ComponentModel;
using System.ComponentModel.Design;
using System.Windows.Forms;
using System.Windows.Forms.Design;

/*
    This sample demonstrates how to perform a series of actions in a designer 
    transaction, how to change values of properties of a component from a 
    designer, and how to complete transactions without being interrupted 
    by other activities.

    To run this sample, add this code to a class library project and compile. 
    Create a new Windows Forms project or load a form in the designer. Add a 
    reference to the class library that was compiled in the first step.
    Right-click the Toolbox in design mode and click Customize Toolbox.  
    Browse to the class library that was compiled in the first step and 
    select OK until the DTComponent item appears in the Toolbox.  Add an 
    instance of this component to the form.  
	
    When the component is created and added to the component tray for your
    design project, the Initialize method of the designer is called. 
    This method displays a message box informing you that designer transaction
    event handlers will be registered unless you click Cancel. When you set 
    properties in the properties window, each change will be encapsulated in 
    a designer transaction, allowing the change to be undone later.  
	
    When you right-click the component,	the shortcut menu for the component 
    is displayed. The designer constructs this menu according to whether 
    designer transaction notifications are enabled, and offers the option
    of enabling or disabling the notifications, depending on the current 
    mode. The shortcut menu also presents a Perform Example Transaction 
    item, which will set the values of the component's StringProperty and 
    CountProperty properties. You can undo the last designer transaction using 
    the Undo command provided by the Visual Studio development environment.
*/

namespace DesignerTransactionSample
{
    // Associate the DTDesigner with this component
    [DesignerAttribute(typeof(DTDesigner))]
    public class DTComponent : System.ComponentModel.Component
    {
    	private string m_String;
	private int m_Count;
			
	public string StringProperty
	{
	    get
            { return m_String; }
	    set
	    { m_String = value; }
	}
			
	public int CountProperty
	{
	    get
	    { return m_Count; }
	    set
	    { m_Count = value; }
	}

	private void InitializeComponent()
	{
	    m_String = "Initial Value";
	    m_Count = 0;
	}
    }
	
    internal class DTDesigner : ComponentDesigner
    {
	private bool notification_mode = false;
	private int count = 10;
		
	// The Verbs property is overridden from ComponentDesigner
	public override DesignerVerbCollection Verbs
	{
	    get
	    {				
	        DesignerVerbCollection dvc = new DesignerVerbCollection();				
		dvc.Add( new DesignerVerb("Perform Example Transaction", new EventHandler(this.DoTransaction)) );
		if(notification_mode)
		    dvc.Add(new DesignerVerb("End Designer Transaction Notifications", new EventHandler(this.UnlinkDTNotifications)));
		else
		    dvc.Add(new DesignerVerb("Show Designer Transaction Notifications", new EventHandler(this.LinkDTNotifications)));				return dvc;
	    }
	}
		
        public override void Initialize(System.ComponentModel.IComponent component)
        {
            base.Initialize(component);

            IDesignerHost host = (IDesignerHost)GetService(typeof(IDesignerHost));			
            if(host == null)
            {
                MessageBox.Show("The IDesignerHost service interface could not be obtained.");
                return;
            }

            if( MessageBox.Show("Press the Yes button to display notification message boxes for the designer transaction opened and closed notifications.","Link DesignerTransaction Notifications?", MessageBoxButtons.YesNo, MessageBoxIcon.Question, MessageBoxDefaultButton.Button1, MessageBoxOptions.RightAlign) == DialogResult.Yes )
            {							
	        host.TransactionOpened += new EventHandler(OnDesignerTransactionOpened);
    	        host.TransactionClosed += new DesignerTransactionCloseEventHandler(OnDesignerTransactionClosed);
                notification_mode = true;
            }
        }
		
        private void LinkDTNotifications(object sender, EventArgs e)
        {
            if(notification_mode == false)
            {
	        IDesignerHost host = (IDesignerHost)GetService(typeof(IDesignerHost));							
                if(host != null)
	        {
		    notification_mode = true;
                   host.TransactionOpened += new EventHandler(OnDesignerTransactionOpened);
                   host.TransactionClosed += new DesignerTransactionCloseEventHandler(OnDesignerTransactionClosed);
	        }
	    }
        }

        private void UnlinkDTNotifications(object sender, EventArgs e)
        {
	    if(notification_mode)
    	    {
    	        IDesignerHost host = (IDesignerHost)GetService(typeof(IDesignerHost));							
	        if(host != null)
                {				
		    notification_mode = false;
                    host.TransactionOpened -= new EventHandler(OnDesignerTransactionOpened);
                    host.TransactionClosed -= new DesignerTransactionCloseEventHandler(OnDesignerTransactionClosed);
                }
            }
        }

        private void OnDesignerTransactionOpened(object sender, EventArgs e)
        {			
	    System.Windows.Forms.MessageBox.Show("A Designer Transaction was started. (TransactionOpened)");
        }

        private void OnDesignerTransactionClosed(object sender, DesignerTransactionCloseEventArgs e)
        {			
	    System.Windows.Forms.MessageBox.Show("A Designer Transaction was completed. (TransactionClosed)");
        }   

        private void DoTransaction(object sender, EventArgs e) 
        {			
    	    IDesignerHost host = (IDesignerHost)GetService(typeof(IDesignerHost));			
            DesignerTransaction t = host.CreateTransaction("Change Text and Size");

            /* The code within the using statement is considered to be a single transaction.
	       When the user selects Undo, the system will undo everything executed in this code block. */
            using (t)
            {
	        if(notification_mode)
	            System.Windows.Forms.MessageBox.Show("Entering a Designer-Initiated Designer Transaction");
				
                // The .NET Framework automatically associates the TypeDescriptor with the correct component
	        PropertyDescriptor someText = TypeDescriptor.GetProperties(Component)["StringProperty"];
                someText.SetValue(Component, "This text was set by the designer for this component.");

                PropertyDescriptor anInteger = TypeDescriptor.GetProperties(Component)["CountProperty"];
	        anInteger.SetValue(Component, count);
	        count++;

                // Complete the designer transaction.
	        t.Commit();
				
	        if(notification_mode)
	            System.Windows.Forms.MessageBox.Show("Designer-Initiated Designer Transaction Completed");
            }
        }
		
	protected override void Dispose(bool disposing)
	{
	    UnlinkDTNotifications(this, new EventArgs());
	    base.Dispose(disposing);
	}
    }
}

System.Object
  System.ComponentModel.Design.DesignerTransaction

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.

Windows 98, Windows Server 2000 SP4, Windows Millennium Edition, Windows Server 2003, Windows XP Media Center Edition, Windows XP Professional x64 Edition, Windows XP SP2, Windows XP Starter Edition

The Microsoft .NET Framework 3.0 is supported on Windows Vista, Microsoft Windows XP SP2, and Windows Server 2003 SP1.

.NET Framework

Supported in: 3.0, 2.0, 1.1, 1.0

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