WPF User Controls in WinForms App

Yes, we really did this!

If you have to maintain a legacy WinForms app, but want to start using WPF components in a legacy application ... this is how you can do just that! 

a bit of background

So, how did we start using WPF components in a legacy application ...Luckily, Microsoft provide an ElementHost class in the System.Windows.Forms.Integration (you will need to add a reference to WindowsFormsIntegration).  The ElementHost class is a WinForms control (System.Windows.Forms.Control) that has a Child property of type UIElement (System.Windows).  This does what we need it to, but if we have a large application which we may be looking to use many WPF controls in, how can we guarantee the ElementHost contains the correct child type?One solution would be to check the child’s type.

ElementHost elementHost = new ElementHost();…if(!(elementHost.Child is ucHelloWorld1)){throw new InvalidOperationException("ElementHost contains the wrong child type!");}

However, this is a run-time check, ideally we want to have a compile-time check to catch these issues early.  Plus this would be something we would have to remember to check each time and that is never a good a thing!  There is a solution.  We make a generic windows form.Now when we have our variable:

frmGenericWPF form ;

We can be assured that it can only contain our user control ucHelloWorld1.

How to make a Generic Windows Form

1. Step one is to get the code-behind file and the designer file open.  If we edit the class definition of the code-behind file, the designer file will be treated as a different class and will not show up in the solution explorer.  This can be done by opening the code-behind, right-clicking the call to InitializeComponents() in the constructor and clicking Go to Definition.

2. Once you have both the files open, add the type parameter to both files.  You will need to have a type constraint to allow the type to be set on your ElementHost class. Something like:

frmGenericWPF where TChild : UIElement

Example Source Code

Code Behind:

using System;using System.Collections.Generic;using System.ComponentModel;using System.Data;using System.Drawing;using System.Linq;using System.Text;using System.Threading.Tasks;using System.Windows.Forms;namespace ElementHostDemo{public partial class frmGenericWPF : Form{public frmGenericWPF(TChild child){InitializeComponent();elementHost1.Child = child;}}}

Designer File:

using System.Windows;namespace ElementHostDemo{partial class frmGenericWPF where TChild : UIElement{/// 
/// Required designer variable./// 

private System.ComponentModel.IContainer components = null;/// 
/// Clean up any resources being used./// 

/// 
true if managed resources should be disposed; otherwise, false.protected override void Dispose(bool disposing){if (disposing && (components != null)){components.Dispose();}base.Dispose(disposing);}#region Windows Form Designer generated code/// 
/// Required method for Designer support - do not modify/// the contents of this method with the code editor./// 

private void InitializeComponent(){this.elementHost1 = new System.Windows.Forms.Integration.ElementHost();this.SuspendLayout();// elementHost1this.elementHost1.Dock = System.Windows.Forms.DockStyle.Fill;this.elementHost1.Location = new System.Drawing.Point(0, 0);this.elementHost1.Name = "elementHost1";this.elementHost1.Size = new System.Drawing.Size(936, 426);this.elementHost1.TabIndex = 0;this.elementHost1.Text = "elementHost1";this.elementHost1.Child = null;// frmGenericWPFthis.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;this.ClientSize = new System.Drawing.Size(936, 426);this.Controls.Add(this.elementHost1);this.FormBorderStyle = System.Windows.Forms.FormBorderStyle.None;this.Name = "frmGenericWPF";this.StartPosition = System.Windows.Forms.FormStartPosition.CenterParent;this.Text = "frmGenericWPF";this.WindowState = System.Windows.Forms.FormWindowState.Maximized;this.ResumeLayout(false);}#endregionprivate System.Windows.Forms.Integration.ElementHost elementHost1;}}

Want to know more?

If you would like to read more on using WPF components in a legacy application, or just take some time to do extra reading around WPF take a look at these articles:MSDN Walkthrough - First WPF ApplicationMSDN - Hosting WPF Composite Control in Windows FormsOr, contact me at QuayTech on info@quaytechsystems.co.uk !