Treat control as either ComboBox or TextBox

Question

What is the best way to solve the following problem?

foreach (Control control in this.Controls)
{
    if (control is ComboBox || control is TextBox)
    {
        ComboBox controlCombobox = control as ComboBox;
        TextBox controlTextbox = control as TextBox;

        AutoCompleteMode value = AutoCompleteMode.None;

        if (controlCombobox != null)
        {
            value = controlCombobox.AutoCompleteMode;
        }
        else if (controlTextbox != null)
        {
            value = controlTextbox.AutoCompleteMode;
        }

        // ...
    }
}

You see it's complicated enough to get the AutoCompleteMode-property. You can assume that it is guaranteed that I have either a ComboBox or a TextBox.

My first idea was to use generic with multiple types for T, but it seems that this is not possible in .NET:

public string GetAutoCompleteModeProperty<T>(T control) where T: ComboBox, TextBox // this does not work, of course

Sadly the both Controls don't have a common base class.

Note: This is meant to be a more general question used with a minimized example. In my case, I also want to access / manipulate other the AutoComplete*-proprties (which also both Controls have in common).

Thanks for ideas!

No, this was meant to be a more general question. This was only a minimized example. I'm also using the AutoComplete*-properties. (I'm adding this to the question now) — The Wavelength, Apr 30 '13 at 07:42
You don't need the outer if do you? If `controlCombobox` is null it is not a ComboBox etc. — MAV, Apr 30 '13 at 07:44
Yeah, you're right. I've only added this to make clear that it is guaranteed that I have either a ComboBox or a TextBox. — The Wavelength, Apr 30 '13 at 07:45
You might want to update your code example with getting the AutoComplete-* properties as well - lots of people are zeroing in on the Text property as the only thing you want, despite your edit :) — Tim, Apr 30 '13 at 07:56

Bogdan M. · Answer 1 · 2013-04-30T08:07:59.070

5

dynamic currentControl =  control;
string text = currentControl.WhatEver;

But, it throws an exception (Microsoft.CSharp.RuntimeBinder.RuntimeBinderException) if currentControl doesn't have WhatEver property

edited Apr 30 '13 at 08:07

answered Apr 30 '13 at 07:53

Bogdan M.

1,128
1
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This works well and seems to be my favorite solution. Thanks. – The Wavelength Apr 30 '13 at 08:07
5

I don't think you should use the `dynamic` keyword in such situations - [see this question](http://stackoverflow.com/q/2674906/463828) – Philipp M Apr 30 '13 at 08:18
Downvote because @PhilippM is right. Using dynamic here is error prone and there are much better ways to go about this. – CodingMadeEasy Jan 13 '15 at 21:10

score 1 · Answer 2 · answered Apr 30 '13 at 07:53

Depends on what you are trying to achieve. If you are just interested in the text property, then this is actually inherited from the Control class - therefore you don't need to cast the object. So you just need :

foreach (var control in this.Controls)
{
    value = control.Text;

    ...
}

If, however, you require more complicated logic, you should consider rethinking your control flow. I would suggest a View / Presenter model and handle each event individually - the approach of single responsibility can greatly reduce the complexity.

If you assign your view an interface with the expected properties - e.g. view.FirstName, view.HouseName or view.CountrySelection - that way the implementation (i.e. TextBox, ComboBox etc) is hidden. So :

public interface IMyView
{
    string FirstName { get; }
    string HouseName { get;}
    string CountrySelection { get; }
}

public class MyView : Form, IMyView
{
    public string FirstName { get { return this.FirstName.Text; } } // Textbox
    public string HouseName { get { return this.HouseName.Text; } } // Textbox
    public string CountrySelection { get { return this.CountryList.Text; } // Combobox
}

I hope that is of some assistance!

`Control.Text` exists only in the winforms library. This is acually a design flaw, since not all controls have a meaningful `Text` property. `System.Windows.Controls.Control` (the WPF version) doesn't have this common property. — MartinStettner, Apr 30 '13 at 07:59

LukeHennerley · Accepted Answer · 2013-04-30T08:00:02.420

1

Use Type.GetType(). You just have to input a string representation of your property in.

if (sender is ComboBox || sender is TextBox)
{
  var type = Type.GetType(sender.GetType().AssemblyQualifiedName, false, true);
  var textValue = type.GetProperty("Text").GetValue(sender, null);
}

This also allows you to set the value of your properties too.

type.GetProperty("Text").SetValue(sender, "This is a test", null);

You could move this to a helper method to save rewriting code.

public void SetProperty(Type t, object sender, string property, object value)
{
  t.GetProperty(property).SetValue(sender, value, null);
}
public object GetPropertyValue(Type t, object sender, string property)
{
  t.GetProperty(property).GetValue(sender, null);
}

There is also room for exception handling by using this method.

var property = t.GetProperty("AutoCompleteMode");
if (property == null)
{
  //Do whatever you need to do
}

edited Apr 30 '13 at 08:00

answered Apr 30 '13 at 07:54

LukeHennerley

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Seems to be a nice solution here which works too. In my case this is too much overhad since I'm trying to do rapid development. Because of this I personally prefer Badgan M.'s solution. Thanks a ton anyway! – The Wavelength Apr 30 '13 at 08:09
1

@TheWavelength you need to consider exception management, this code is easier to maintain because we know whether or not the propert exists. With dynamic, it gets the property at runtime and there is no way to check unless you wrap it in a try catch. The overhead of this really isn't that much :) – LukeHennerley Apr 30 '13 at 08:10
@TheWavelength if the understanding of this is what you are struggling on, I can explain further :) – LukeHennerley Apr 30 '13 at 08:13
Well, you're right. It is even "faster" (in meaning of typing the code) to use your solution because I can miss the try-catch-block. Thanks! No explanation needed, I think I've got it ;) – The Wavelength Apr 30 '13 at 08:17

Treat control as either ComboBox or TextBox

3 Answers3