C# User Control - How to tell containing object the control needs data

I am creating a C# WinForm开发者_开发技巧s user control. There will be times when the user control will need data from the form it's contained in. How do I go about having the user control tell the form containing it that it needs some data?

Thanks!

You can subscribe the form to an event raised on the UserControl.

Your archiecture dictates where and when you need to subscribe to the data event. We can't answer that without knowing a little more about how your whether you are adding the control at runtime or design time. Each case will require a little derivation. From the perspective of adding your control at runtime, you could do something similar to the following:

// Your sample control
public class MyUserControl : Control
{
    public event EventHandler<EventArgs> INeedData;
    public Data Data {get; set;}

    private class DoSomething()
    {
        if(INeedData!=null) INeedData(this,null);
    }
}

...

// Your Form, in the case that the control isn't already added.
var _myUserControl = new MyUserControl();
private void Form1_Load(object sender, EventArgs e)
{
    _myUserControl.INeedData += new EventHandler<EventArgs>(MyUserControl_INeedData);
    this.Controls.Add(myUserControl);
}

void MyUserControl_INeedData(object sender, EventArgs e)
{
    _myUserControl.Data = SomeData;
}

Create a custom event in the user control and have the form hook into it. If you need custom event arguments, you can create those too.

In user control:

//Define your Custom Event argument
public class MyEventArgs : EventArgs
{
    //Define some fields of your custom event argument
    private int m_SomeValue = 0;

    //Define some properties of your custom event argument
    public int SomeValue
    {
        get { return m_SomeValue; }
        set { m_SomeValue = value; }
    }
}

//Define the event handler data type
public delegate void MyEventHandler(object sender, MyEventArgs e);

//Define the object which holds the outside event handlers
public event MyEventHandler SomeEvent;

//Define the function which will generate the event
public virtual void OnSomeEvent(MyEventArgs e)
{
    if (SomeEvent != null)
        SomeEvent(this, e);
}

.
. //Then later in the control
.
{
    //We need new data

    //Create the event arguments
    MyEventArgs newEvent = new MyEventArgs();

    //Set the values
    newEvent.SomeValue = 17;

    //Call the event generating function
    OnSomeEvent(newEvent);
}

In your form just use something like:

myControl.SomeEvent += new MyEventHandler(handlerName);

Since your event is public, you should see it in the Properties window of your control as well.

You can fancy up the event using Metadata attributes, but I leave it up to you to discover these.

Create an event on the user control where the event args are editable. Let the form attach a handler to that event, which updates those fields. Use those fields in the OnEvent method.

[untested] eg.

public delegate void NeedsUserDataEventHandler(object sender, NeedsUserDataEventArgs args);

public class NeedsUserDataEventArgs : EventArgs
{
    public UserData UserData { get; set; }
}

// In Control
public event NeedsUserDataEventHandler NeedsUserData;

public void OnNeedsUserData(NeedsUserDataEventArgs args)
{
    NeedsUserDataEventHandler handler = NeedsUserData;
    if (handler != null) handler(this, args);
    // store your data somewhere here
}

// In Form
public override void OnLoad(object sender, EventArgs args)
{
    control.NeedsUserData += ControlNeedsUserData;
}

public override void OnClosed(object sender, EventArgs args)
{
    control.NeedsUserData -= ControlNeedsUserData;
}

public void ControlNeedsUserData (object sender, NeedsUserDataEventArgs args)
{
    args.UserData = // set whatever here
}

Seems a bit vague to me, but:

Make it an event in the containing WinForm, so that every time some data is ready all the subscribers can be notified in a one-to-many model; or make it an event in the subscribed control, in a one-to-one model, in which it calls the container's method that retrieves such data?

It's dependent on when that data needs to be pushed to the UserControl. Are there events taking place on the Form that will drive the need to move data within the UserControl? If so...simply grab your instance at that point and push the data down to the UserControl via a public property.

If this is a case where events are not being used or the Form in some fashion or another "receives the data" then exposing an event on the Form such as...

public event DataHandler ReceivedData;

...and allow the UserControl or any other container to register for the event and receive the data via your custom event args. Pushing the event into the UserControl and forcing the Form to latch onto the UserControl seems backwards since the Form is the initiator of the data.