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MouseEventArgs.Delta Property

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Definition

Namespace:
System.Windows.Forms
Assembly:
System.Windows.Forms.dll

Gets a signed count of the number of detents the mouse wheel has rotated, multiplied by the WHEEL_DELTA constant. A detent is one notch of the mouse wheel.

public:
 property int Delta { int get(); };
public int Delta { get; }
member this.Delta : int
Public ReadOnly Property Delta As Integer

Property Value

Int32

A signed count of the number of detents the mouse wheel has rotated, multiplied by the WHEEL_DELTA constant.

Examples

The following code example demonstrates the use of this member. In the example, an event handler reports on the occurrence of the Control.MouseClick event. This report helps you learn when the event occurs and can assist you in debugging. To report on multiple events or on events that occur frequently, consider replacing MessageBox.Show with Console.WriteLine or appending the message to a multiline TextBox.

To run the example code, paste it into a project that contains an instance of a type that inherits from Control, such as a Button or ComboBox. Then name the instance Control1 and ensure that the event handler is associated with the Control.MouseClick event.

private void Control1_MouseClick(Object sender, MouseEventArgs e) {

System.Text.StringBuilder messageBoxCS = new System.Text.StringBuilder();
messageBoxCS.AppendFormat("{0} = {1}", "Button", e.Button );
messageBoxCS.AppendLine();
messageBoxCS.AppendFormat("{0} = {1}", "Clicks", e.Clicks );
messageBoxCS.AppendLine();
messageBoxCS.AppendFormat("{0} = {1}", "X", e.X );
messageBoxCS.AppendLine();
messageBoxCS.AppendFormat("{0} = {1}", "Y", e.Y );
messageBoxCS.AppendLine();
messageBoxCS.AppendFormat("{0} = {1}", "Delta", e.Delta );
messageBoxCS.AppendLine();
messageBoxCS.AppendFormat("{0} = {1}", "Location", e.Location );
messageBoxCS.AppendLine();
MessageBox.Show(messageBoxCS.ToString(), "MouseClick Event" );
}

Private Sub Control1_MouseClick(sender as Object, e as MouseEventArgs) _ 
     Handles Control1.MouseClick

    Dim messageBoxVB as New System.Text.StringBuilder()
    messageBoxVB.AppendFormat("{0} = {1}", "Button", e.Button)
    messageBoxVB.AppendLine()
    messageBoxVB.AppendFormat("{0} = {1}", "Clicks", e.Clicks)
    messageBoxVB.AppendLine()
    messageBoxVB.AppendFormat("{0} = {1}", "X", e.X)
    messageBoxVB.AppendLine()
    messageBoxVB.AppendFormat("{0} = {1}", "Y", e.Y)
    messageBoxVB.AppendLine()
    messageBoxVB.AppendFormat("{0} = {1}", "Delta", e.Delta)
    messageBoxVB.AppendLine()
    messageBoxVB.AppendFormat("{0} = {1}", "Location", e.Location)
    messageBoxVB.AppendLine()
    MessageBox.Show(messageBoxVB.ToString(),"MouseClick Event")

End Sub

Remarks

The mouse wheel combines the features of a wheel and a mouse button. The wheel has discrete, evenly spaced notches. When you rotate the wheel, a wheel message is sent as each notch is encountered. One wheel notch, a detent, is defined by the windows constant WHEEL_DELTA, which is 120. A positive value indicates that the wheel was rotated forward (away from the user); a negative value indicates that the wheel was rotated backward (toward the user).

Currently, a value of 120 is the standard for one detent. If higher resolution mice are introduced, the definition of WHEEL_DELTA might become smaller. Most applications should check for a positive or negative value rather than an aggregate total.

Applies to

See also