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I've got some code to indicate when a field on my WinForm has changed.

If the Control is a TextBox, I alter the ForeColor and BackColor depending on if the Text of the Control is equal to the default (or initial) value.

private void LastName_Changed(object sender, EventArgs e) { if (sender.Equals(txtLastName)) { if (emp0.LastName != txtLastName.Text) { txtLastName.ForeColor = changedTxtFont; txtLastName.BackColor = changedTxtBack; btnOK.Enabled = true; } else { txtLastName.ForeColor = systemTxtFont; txtLastName.BackColor = systemTxtBack; } AuthenticationReset(); } }

If the Control is a DateTimePicker or ComboBox, I can't really do this (there is no visible ForeColor or BackColor), so I alter the Label that is associated with the Control.

private void TrainDate_Changed(object sender, EventArgs e) { if (sender.Equals(dtTrainDate)) { DateTime trainDate = Global.SqlDate(emp0.TrainDate); if (trainDate != dtTrainDate.Value) { lblTrainDate.ForeColor = changedLblFont; lblTrainDate.BackColor = changedLblBack; btnOK.Enabled = true; } else { lblTrainDate.ForeColor = systemLblFont; lblTrainDate.BackColor = systemLblBack; } AuthenticationReset(); } }

I'd like to create some sort of Extension Method that could change the ForeColor and BackColor of a Control dependent upon what that Control is and if the value had changed.

Here is an attempt, but the use of this in the code is not valid and the extension methods do not show up for any of the Controls I want to use them on.

public static class ColorChange { public static Color ForeColorChange(this Color owned, bool changed) { if (this is TextBox) { return changed ? Color.Red : SystemColors.WindowText; } else { return changed ? Color.Red : SystemColors.ControlText; } } public static Color BackColorChange(this Color owned, bool changed) { if (this is TextBox) { return changed ? Color.Yellow : SystemColors.Window; } else { return SystemColors.Control; } } }

Is there a way to approach what I'm trying to do or is this not what Extension Methods are for?

I'd like to end up with something like this:

private void TrainDate_Changed(object sender, EventArgs e) { if (sender.Equals(dtTrainDate)) { DateTime trainDate = Global.SqlDate(emp0.TrainDate); if (trainDate != dtTrainDate.Value) { lblTrainDate.ForeColorChange(true); lblTrainDate.BackColorChange(true); btnOK.Enabled = true; } else { lblTrainDate.ForeColorChange(false); lblTrainDate.BackColorChange(false); } AuthenticationReset(); } }

Solution:

Using the answer checked below, I wrote the following Extension Method:

public static class ColorChange { public static void AlteredText(this Control owned, bool changed) { if (owned is TextBox) { owned.ForeColor = changed ? Color.Red : SystemColors.WindowText; owned.BackColor = changed ? Color.Yellow : SystemColors.Window; } else { owned.ForeColor = changed ? Color.Red : SystemColors.ControlText; owned.BackColor = SystemColors.Control; } } }

Here is how I will be using it:

private void TrainDate_Changed(object sender, EventArgs e) { if (sender.Equals(dtTrainDate)) { DateTime trainDate = Global.SqlDate(emp0.TrainDate); if (trainDate != dtTrainDate.Value) { lblTrainDate.AlteredText(true); btnOK.Enabled = true; } else { lblTrainDate.AlteredText(false); } AuthenticationReset(); } }

I hope others get use out of this as well. ~Joe.

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  • 1
    Are those methods declared in a static class?: Commented Aug 24, 2012 at 16:24
  • Yes. I do have a static class that they are defined in. Good question! Commented Aug 24, 2012 at 16:25
  • So try calling them like (TextBox(Control)).ForeColor.ForeColorChange(true); Commented Aug 24, 2012 at 16:27

4 Answers 4

Reset to default
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You've defined extension methods for the Color class, not Control, which is why it won;t show for controls. In addition, your methods probably want to inspect the owned control that you'll need to pass in.

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1

This extends Control instead of Color (needs to be defined in a static class):

public static void ForeColorChange(this Control owned, bool changed) { if (owned is TextBox) { owned.ForeColor = changed ? Color.Red : SystemColors.WindowText; } else { owned.ForeColor = changed ? Color.Red : SystemColors.ControlText; } } public static void BackColorChange(this Control owned, bool changed) { if (owned is TextBox) { owned.BackColor = changed ? Color.Yellow : SystemColors.Window; } else { owned.BackColor = SystemColors.Control; } }

Usage:

TextBox box = ...; box.ForeColorChange(true);
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+1. You're' onto something, and I'm understanding it (says a lot). The 2nd method still shows a Color type, but I understand what you are saying.
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If you want to call your extension method on your textbox, you have to do this in the toplevel of your namespace:

public static class Extensions { public static void myExtensionMethod(this Textbox textbox) { //Do what you want to do } }

And then it is accessible over your textbox:

Textbox myTextbox = new Textbox(); myTextbox.myExtensionMethod();

If you want, you can also pass parameters to your extension method.

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This technique can not be general enough to use with the Label controls, too, though. ...if I'm not mistaken.
In general, it works with a Label, too. But Label does not inherit Control. So if you extend the Control class, the label does not know about it. If you need to have a single method that always works, you could create a custom DateTimePicker/ComboBox and attach a label there. Then these controls have a handle to the Label and the extension method can change it.
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Use your owned instead of this.. oh and as Rowland Shaw says, Control instead of Color.

So your code should finally be

public static Color ForeColorChange(this Control owned, bool changed) { if (owned is TextBox) { return changed ? Color.Red : SystemColors.WindowText; } else { return changed ? Color.Red : SystemColors.ControlText; } } public static Color BackColorChange(this Control owned, bool changed) { if (owned is TextBox) { return changed ? Color.Yellow : SystemColors.Window; } else { return SystemColors.Control; } }
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