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Form.TopLevel Property

Gets or sets a value indicating whether to display the form as a top-level window.

Namespace:  System.Windows.Forms
Assembly:  System.Windows.Forms (in System.Windows.Forms.dll)
[BrowsableAttribute(false)]
public bool TopLevel { get; set; }

Property Value

Type: System.Boolean
true to display the form as a top-level window; otherwise, false. The default is true.
ExceptionCondition
Exception

A Multiple-document interface (MDI) parent form must be a top-level window.

A top-level form is a window that has no parent form, or whose parent form is the desktop window. Top-level windows are typically used as the main form in an application.

The following code example use the Modal property to determine if a form is displayed as a modal form. If it is not the FormBorderStyle and TopLevel properties are changed to make the form non-top-level form with a tool window border.

		private void ShowMyNonModalForm()
		{
			Form myForm = new Form();
			myForm.Text = "My Form";
			myForm.SetBounds(10,10,200,200);

			myForm.Show();
			// Determine if the form is modal. 
			if(myForm.Modal == false)
			{
				// Change borderstyle and make it not a top level window.
				myForm.FormBorderStyle = FormBorderStyle.FixedToolWindow;
				myForm.TopLevel = false;
			}
		}

.NET Framework

Supported in: 4.5.1, 4.5, 4, 3.5, 3.0, 2.0, 1.1, 1.0

.NET Framework Client Profile

Supported in: 4, 3.5 SP1

Windows Phone 8.1, Windows Phone 8, Windows 8.1, Windows Server 2012 R2, Windows 8, Windows Server 2012, Windows 7, Windows Vista SP2, Windows Server 2008 (Server Core Role not supported), Windows Server 2008 R2 (Server Core Role supported with SP1 or later; Itanium not supported)

The .NET Framework does not support all versions of every platform. For a list of the supported versions, see .NET Framework System Requirements.

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