组合多个控件的控件子类

Question

I'm trying to extend TextBox to add a Label to the left of it and treat it as one Control so I don't have to keep track of both of their sizes, locations, etc.

I've created a TextBoxWithLabel class that extends Control and has TextBox and Label fields, but I'm not really sure what to do for onPaint() - do I have to tell it to manually draw both items? If so, how? I'm guessing the default inherited behaviour doesn't go so far as 'check if I contain any child Controls and if I do, draw them'...

Is this even the best way to do it? I previously had my class extend TextBox and just added the Label field, but of course that didn't get added to the Panel containing the TextBoxWithLabel and so wasn't drawn.

Any suggestions or pokes in the right direction appreciated.

Thanks,

Alex

Answer 1

The typical approach here is a UserControl in which you put both the label and the text box. It is painful though, you have to add a lot of the properties and events of the text box to the user control so it at least resembles a text box. Ugly boilerplate code.

Another way to do it is to make a custom text box that sneaks in a label control on the parent. That completely behaves like a TextBox without having to do any work. Add a new class to your project and paste the code shown below. Compile. Drop the new control from the top of the toolbox onto your form. Set the Description property to the text you want to see appear in the label.

using System;
using System.Drawing;
using System.Windows.Forms;

class MyTextBox : TextBox {
    private Label label;
    public MyTextBox() {
        label = new Label();
        label.AutoSize = true;
        label.Font = this.Font;
        label.Location = this.Location;
        label.Resize += new EventHandler(label_Resize);
    }
    protected override void OnParentChanged(EventArgs e) {
        // Keeps label on the same parent as the text box
        base.OnParentChanged(e);
        label.Parent = this.Parent;   // NOTE: no dispose necessary
    }

    private void moveLabel() {
        // Keep label right-aligned to the left of the text box
        label.Location = new Point(this.Left - label.Width - 10, this.Top);
    }
    private void label_Resize(object sender, EventArgs e) {
        moveLabel();
    }
    protected override void OnLocationChanged(EventArgs e) {
        base.OnLocationChanged(e);
        moveLabel();
    }

    public string Description {
        get { return label.Text; }
        set { label.Text = value; }
    }

    public override Font Font {
        get { return base.Font; }
        set { base.Font = label.Font = value; }
    }

}

Answer 2

Did you consider using a UserControl? The benefit of a usercontrol is that you can easily put your label and textbox with correct relative positioning.

Answer 3

• Custom Control - An extension to an existing control
• User Control - A composition of multiple existing controls

Choose your candidate.