How to set a property by calling a method

Question

Hello,

I'd like to know how to set a custom property of a custom user control by calling a method that would serve as "data provider" for that property.

What I mean is I'd like to write something like this:

<CatsUserControl Cats={FindAllCats} />,

where CatsUserControl is a User Control I created (which has a Property named Cats), and FindAllCats() is a method written in C# that returns a list of Cat objects.

Is this possible?

I appreciate any ideas. Thanks!

EDIT:

The whole thing began because I wanted to be able to assign a list to a property in XAML, the same way you do <Button Content="Value"/> (except, in my case, Value is a more complex type than a string, it's a List<KeyValuePair<String, Boolean>>).

Because I didn't find any way to do that, I thought it might be possible to call a method that returns this list and assign the returned value to the property instead.

Hope that makes things clearer.

Answer 1

It seems like what you are trying to do is really just databinding?

In other words, you would approach it like this:

<CatsUserControl ItemsSource="{Binding AllCats}" />

Binding to a collection

If you want to bind specifically to a property called Cats you need to create an object that implements INotifyPropertyChanged, I think. (semi-pseudo code follows):

//binding to this public property in the CatsUserControl    
public List<Cat> Cats;


public class BindingToCats : INotifyPropertyChanged
{
    private List<Cat> allCats;

    public List<Cat> AllCats
    {
        get { return allCats; }
        set
        {
            allCats = value;
            OnPropertyChanged("AllCats");
        }
    }

    public event PropertyChangedEventHandler PropertyChanged;

    protected virtual void OnPropertyChanged(string propertyName)
    {
        if (PropertyChanged != null)
        {
            PropertyChanged(this, new PropertyChangedEventArgs(propertyName));
        }
    }
}

and then bind to it with your custom usercontrol:

<CatsUserControl Cats="{Binding AllCats, Source={StaticResource BindingToCats}}" />

Answer 2

You ought to be able to do what you're asking by subscribing to events instead of binding directly from the XAML.

Also, you could use a converter, which is described here.

Answer 3

What you are probably looking for is a TypeConverter.

Here is an example of how you can set a List< KeyValuePair< String, Boolean>> using a string in attribute syntax in xaml. The Xaml will end up looking something like:

<c:CustomButton Values="Hello World,true; Foo,false; Bar,true" />

The exact syntax of how you want to represent the list of key/value pairs is up to you.

Here is the code necessary to do this:

public class CustomButton : Button
{
    [TypeConverter(typeof(ListOfStringAndBoolPairsTypeConverter))]
    public List<KeyValuePair<String, Boolean>> Values { get; set; }
}

public class ListOfStringAndBoolPairsTypeConverter : TypeConverter
{
    public override object ConvertFrom(ITypeDescriptorContext context, System.Globalization.CultureInfo culture, object value)
    {
        //TODO: Should add better error handling here.
        var stringValue = (string)value;
        var pairs = stringValue.Split(';').Select(ps => ParsePair(ps));

        var result = new List<KeyValuePair<String, Boolean>>();
        result.AddRange(pairs);
        return result;
    }

    private KeyValuePair<String, Boolean> ParsePair(string pairStringValue)
    {
        var splitString = pairStringValue.Split(',');
        var key = splitString[0];
        var value = Boolean.Parse(splitString[1].Trim());
        return new KeyValuePair<string, bool>(key, value);
    }
}