Show All TextBox Text After Resize

• Download source code - C# - 15.4 KB
• Download source code - VB.NET - 20.7 KB

Introduction

If you have a TextBox that is too narrow to display all its text, it will show the end of the text on startup:

If you resize it to a width that could display the whole string, the TextBox will not reposition the text to show all text:

This code will reset the text position to show all text, while maintaining any text selection and carat position.

Background

The .NET TextBox control is merely a wrapper for the old Win32 edit box control. This limits its functionality, and makes it difficult to customize. Even simple tasks like resizing the height of the TextBox require you to use complex workarounds to accomplish.

When you resize a TextBox where some of the text is off the left edge of the control, it never repositions the text to show as much as the control will handle. To overcome this limitation, we need to modify the TextBox text selection.

Using the code

To reset the visible text in the TextBox, we need to change the carat (cursor) position to the beginning of the string, then back to the end. However, doing this will lose any selection that the user might have made prior to the resize. This routine will determine what is selected in the control, reset the carat location, then restore the user's selection.

Visual Basic:

Private Sub SetAllTextVisible(ByRef tbTextBox As TextBox)
    Dim iSelectStart As Integer
    Dim iSelectLength As Integer

    ' Get the current selection so we can re-select it.
    iSelectStart = tbTextBox.SelectionStart
    iSelectLength = tbTextBox.SelectionLength

    ' De-select everything and set the cursor to
    ' the start of the line
    tbTextBox.Select(0, 0)
    tbTextBox.SelectionStart = 0

    ' Restore the user's original selection
    tbTextBox.Select(iSelectStart, iSelectLength)
End Sub

C#:

public void SetAllTextVisible(TextBox tbTextBox)
{
    int startselect;
    int selectlength;

    // Get the current selection so we can re-select it
    startselect = tbTextBox.SelectionStart;
    selectlength = tbTextBox.SelectionLength;
    // De-select everything and set the cursor to the
    // start of the line.
    tbTextBox.Select(0, 0);
    tbTextBox.SelectionStart = 0;

    // Restore the user's original selection
    tbTextBox.Select(startselect, selectlength);
}

User Control

Alternatively, you could create a new UserControl class and change the inheritance on the class declaration from UserControl to TextBox. Override the OnSizeChanged event to call the SetAllTextVisible routine.

Important: If you change a class inheritence from UserControl to TextBox, you will need to open the UserControll.Designer code and remove the Autoscale property:

private void InitializeComponent()
{
    components = new System.ComponentModel.Container();
    //Comment the line below when changing inheritence from UserControl
    //to Textbox.
    //this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
}

public partial class ShowAllTextBox : TextBox
{
    public ShowAllTextBox()
    {
        InitializeComponent();
    }

    protected override void OnSizeChanged(EventArgs e)
    {
        SetAllTextVisible();
        base.OnSizeChanged(e);
    }

    public void SetAllTextVisible()
    {
        int startselect;
        int selectlength;

        // Get the current selection so we can re-select it
        startselect = this.SelectionStart;
        selectlength = this.SelectionLength;
        // De-select everything and set the cursor to the
        // start of the line.
        this.Select(0, 0);
        this.SelectionStart = 0;

        // Restore the user's original selection
        this.Select(startselect, selectlength);
    }
}

Enjoy!