Changing the text color of a disabled RadTextBox

Product Version	Product	Author	Last modified
Q2 2011 SP1	RadTreeView for WinForms	Nikolay Diyanov	Oct 4, 2011

PROBLEM

Our editor controls (RadDropDownList, RadTextBox, RadSpinEditor, RadMaskedEditBox and RadDateTimePicker) use the standard Microsoft TextBox for the textbox part. You can easily change the BackColor of a TextBox if it is disabled. However, the TextBox implementation does not provide any means for changing the color of the the text of a disabled TextBox instance.

SOLUTION

In order to work around this limiation, you can create a custom TextBox instance that does not use the default text painting, but uses its own text painting instead. Then, you can add this custom instance in the structure of a Rad editor and display it only if the Rad editor becomes disabled.

Let's take and analyze the case of RadTextBox: 1.First, we should create a custom TextBox instance. Our editors use an extended TextBox implementation called HostedTextBoxBase. Therefore, our class should derive from HostedTextBoxBase. In the body of our class, we should override the OnPaint method where we should draw our own text. In addition, we should call the SetStyle in the constructor of the customized HostedTextBoxBase, passing the ControlStyles.UserPaint as a parameter. Please note that the color of the text that we will draw is Red:

public class MyTextBox : HostedTextBoxBase
{
    public MyTextBox()
    {
        this.SetStyle(ControlStyles.UserPaint, true);
    }

    protected override void OnPaint(PaintEventArgs e)
    {
        SolidBrush drawBrush = new SolidBrush(Color.Red); 
        e.Graphics.DrawString(Text, Font, drawBrush, -1f, -1f);
    }
}

Public Class MyTextBox
    Inherits HostedTextBoxBase
    Public Sub New()
        Me.SetStyle(ControlStyles.UserPaint, True)
    End Sub

    Protected Overrides Sub OnPaint(ByVal e As PaintEventArgs)
        Dim drawBrush As New SolidBrush(Color.Red)
        e.Graphics.DrawString(Text, Font, drawBrush, -1f, -1f)
    End Sub
End Class

2.Now it is time to create a descendant of RadTextBox. In this descendant we should create a RadTextBoxItem - this is an element of our framework that will host the customized HostedTextBoxBase. We can add the created RadTextBoxItem object to the structure of the control in the overridden CreateChildItems method. We should also override the OnEnabledChanged method. In this method we hide the default RadTextBoxItem instance so that the new one can be displayed. Finally, in order to keep the appropriate styling of the control, we should override the ThemeClassName property:

public class MyRadTextBox : RadTextBox
{       
    MyTextBox mtb = new MyTextBox();
    RadTextBoxItem tbi;

    protected override void CreateChildItems(Telerik.WinControls.RadElement parent)
    {
        base.CreateChildItems(parent);

        tbi = new RadTextBoxItem(mtb);
        mtb.Font = this.Font;
        this.TextBoxElement.Children.Add(tbi);     
    }

    protected override void OnEnabledChanged(EventArgs e)
    {
        if (!this.Enabled)
        {
            tbi.Text = this.Text;
            this.TextBoxElement.TextBoxItem.Visibility = Telerik.WinControls.ElementVisibility.Hidden;
        }
        else
        {
            this.TextBoxElement.TextBoxItem.Visibility = Telerik.WinControls.ElementVisibility.Visible;
        }

        base.OnEnabledChanged(e);
    }

    public override string ThemeClassName
    {
        get
        {
            return typeof(RadTextBox).FullName;
        }
    }

}

Public Class MyRadTextBox
    Inherits RadTextBox

    Private mtb As MyTextBox
    Private tbi As RadTextBoxItem

    Protected Overrides Sub CreateChildItems(ByVal parent As Telerik.WinControls.RadElement)
        MyBase.CreateChildItems(parent)

        mtb = New MyTextBox()
        tbi = New RadTextBoxItem(mtb)
        mtb.Font = Me.Font
        Me.TextBoxElement.Children.Add(tbi)
    End Sub

    Protected Overrides Sub OnEnabledChanged(ByVal e As EventArgs)
        If Not Me.Enabled Then
            tbi.Text = Me.Text
            Me.TextBoxElement.TextBoxItem.Visibility = Telerik.WinControls.ElementVisibility.Hidden
        Else
            Me.TextBoxElement.TextBoxItem.Visibility = Telerik.WinControls.ElementVisibility.Visible
        End If

        MyBase.OnEnabledChanged(e)
    End Sub

    Public Overrides Property ThemeClassName() As String
        Get
            Return GetType(RadTextBox).FullName
        End Get
        Set(ByVal value As String)

        End Set
    End Property
End Class

The approach regarding the rest of the editors is similar. Please find a sample project below which demonstrates the approach for RadTextBox, RadSpinEditor, RadMaskedEditBox, RadDateTimePicker and RadDropDownList.

You can download a complete VB and C# project from the following link.