6

I have a custom DataGridView, let's say as such:

public MyGridView : DataGridView
{
    public MyGridView()
    {
         BackgroundColor = Color.Red;
    }
}

Now, when I use this control in a project using the designer, for some reason it feels a need to also set the property in the designer.cs file.

So in the designer file, I would have:

this.MyGridView1.BackgroundColor = System.Drawing.Color.FromArgb((byte)(int)255, (byte)(int)0, (byte)(int)0);

The problem me with this is that it prevents me from being able to change the color in the constructor of my MyGridView, without having to go through all the forms in which I used to control and change it per instance, rendering my custom control useless.

With some properties which offer a virtual getter, this is no problem, but most properties do not have it.

How can I prevent the designer from generating this code?

Rotem
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  • Decorate property with [DefaultValue](http://msdn.microsoft.com/en-us/library/system.componentmodel.defaultvalueattribute%28v=vs.110%29.aspx) attribute. – Nikola Markovinović Dec 30 '13 at 09:27
  • @NikolaMarkovinović These are not properties I've created, these are properties inherited from `DataGridView` (.e.g `BackgroundColor`). Where would I add the attribute? – Rotem Dec 30 '13 at 09:28
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    Serves me right for not reading the question throughly. I don't think that there is an *acceptable* solution. You might hide original property as they did in [this answer](http://stackoverflow.com/questions/163611/changing-the-defaultvalue-of-a-property-on-an-inherited-net-control) dealing with inherited ComboBox. Again, my apologies. – Nikola Markovinović Dec 30 '13 at 09:42
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    @NikolaMarkovinović No problem! At least you gave it some attention :) The question you linked is a possible workaround, but it only works for `const`able values. Is there a way to assign a default value attribute to non-`const`able value types? – Rotem Dec 30 '13 at 09:55

4 Answers4

13

I should emphasize that this isn't normally the way you do this, the [DefaultValue] attribute is normally the correct choice. But you are working with a property of type Color, it is not simple to write the attribute for that in a flexible way. The arguments you can pass to an attribute constructor can be only a select few data types, Color isn't one of them. You'd have to craft a string that ColorConverter can understand, that's both ugly and hard to maintain.

PropertyGrid has a secondary way of providing defaults for "difficult" properties, it will also look for specially named private members in the class. Given a property named "Xxxx", it looks for the following:

  • DefaultXxxx, a property with just a getter that returns the default value
  • ResetXxxx(), a method that can run when the user selects the Reset context menu item
  • ShouldSerializeXxxx(), a method that should return false if the value of the property should not be persisted.

Which makes this code work:

public class MyGridView : DataGridView {
    public MyGridView() {
        this.BackgroundColor = DefaultBackgroundColor;
    }
    public new Color BackgroundColor {
        get { return base.BackgroundColor; }
        set { base.BackgroundColor = value;  }
    }
    private bool ShouldSerializeBackgroundColor() {
        return !this.BackgroundColor.Equals(DefaultBackgroundColor);
    }
    private void ResetBackgroundColor() {
        this.BackgroundColor = DefaultBackgroundColor;
    }
    private static Color DefaultBackgroundColor {
        get { return Color.Red; }
    }
}

Note that the ResetBackgroundColor() method is not actually necessary since no special effects are required when the user resets the property, I just included it for completeness.

Hans Passant
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  • How would you go about doing this for something another level deep like the AlternatingRowsDefaultCellStyle.BackColor property? – thegaffney Aug 29 '16 at 16:01
  • This approach works for any property of type Color, BackgroundColor was just an example. Changing the DataGridView.AlternatingRowsDefaultCellStyle property just takes a lot more work since you don't just have to change the Color, you also have to provide the DataGridViewCellStyle instance. Click the Ask Question button to get help. – Hans Passant Aug 29 '16 at 16:23
  • The `ResetXxxx()` and `ShouldSerializeXxxx()` methods are documented [here](https://learn.microsoft.com/en-us/dotnet/desktop/winforms/controls/defining-default-values-with-the-shouldserialize-and-reset-methods). Did someone find official documentation for the `DefaultXxxx` property mechanism? – tm1 Sep 03 '20 at 10:31
3

There is a simpler way to assign DefaultValue to Color:

public class MyGridView : DataGridView
{
    public MyGridView()
    {
        BackgroundColor = Color.Red;
    }

    [DefaultValue(typeof(Color), "Red")]
    public new Color BackgroundColor
    {
        get { return base.BackgroundColor; }
        set { base.BackgroundColor = value; }
    }
}
yclkvnc
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2

Try using InitLayout instead and DesignMode. You can't use DesignMode in the ctor, but after the control is constructed you can access the Designmode property correctly to set the colour. Note: this will not be styled in the designer, just at run time.

public class MyGridView : DataGridView
{

    protected override void InitLayout()
    {
        base.InitLayout();

        if (!DesignMode)
            BackgroundColor = Color.Red;
    }
}
Jay
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  • Thanks, this is a reasonable compromise. I am using it instead in the `OnHandleCreated` method, for reasons specific to my project. – Rotem Dec 30 '13 at 10:20
0

If needs are simple and design appearance is no issue, try writing an extension or two, e.g.,

public static class Extensions
{
    public static void ApplyStyle( this DataGridView dataGridView )
    {
        dataGridView.RowHeadersVisible = false;
        ...
    }
}
Paul Embleton
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