How do you pass parameters from xaml?

问题:

I have created my own UserControl "ClockControl", which I initialize through the main window's XAML.

The only problem is that I have to pass a parameter to the constructor of the clock control, and I have no clue of I how I can do that.

This works if I have no parameters:

<myControl:ClockControl></myControl:ClockControl>

But how can I pass a parameter doing this?

Here is the constructor:

public ClockControl(String city)
    {
        InitializeComponent();
        this.initController();
        ......
        .....
    }

Thanks in advance.

回答1:

Your constructor:

public ClockControl(String city)
{
    InitializeComponent();
    this.initController();
    //...
}

First of all, if you want to use ClockControl from XAML, then you need a default constructor, means a constructor which doesn't take any parameter. So the above constructor is not going to work.

I would suggest you to define a property with name City, preferably dependency property, and then use it from XAML. Something like this:

public class ClockControl: UserControl
    {
        public static readonly DependencyProperty CityProperty = DependencyProperty.Register
            (
                 "City", 
                 typeof(string), 
                 typeof(ClockControl), 
                 new PropertyMetadata(string.Empty)
            );

        public string City
        {
            get { return (string)GetValue(CityProperty); }
            set { SetValue(CityProperty, value); }
        }

        public ClockControl()
        {
            InitializeComponent();
        }
        //..........
}

Then you can write this in XAML:

<myControl:ClockControl City="Hyderabad" />

Since City is a dependency property, that means you can even do Binding like this:

<myControl:ClockControl City="{Binding Location}" />

Hope, that solves your problem!

回答2:

This is done with the use of DependencyProperty's, however not via the constructor. Just by adding properties to the control itself and using them from the code-behind.

Have a read of the following in regards to DependencyProperty's:

• Dependency Properties Overview
• DependencyProperty Class MSDN
• Why Dependency Properties?

As a visual note, what this will allow you to do is the following, and then use it in the code-behind:

<myControl:ClockControl City="New York"></myControl:ClockControl>

回答3:

x:Arguments directive would be what you need.

回答4:

Could simplify this by simply binding the Tag property of the control. Quick and dirty, and perhaps not overly elegant, but saves times adding another property.