访问动态加载的用户控制方法

Question

I'm stuck in a problem and would appreciate any help or pointers I can get. I'm trying to develop an application that based on a user choice, loads a given user control to gather some info. All of the user controls are custom made but all of them have the same public methods - clear, get a string value, etc. During the execution of the application I need to be able to call those methods. This is what I've tried:

public partial class frmDesktop : Form
{
    private UserControl active = new UserControl;

    private UserControl GetActiveUsrCtrl(AppEnum.Catalog catalogId, frmMain parent)
    { 
        UserControl ctrl= null;

        switch (catalogId)
        {
            case AppEnum.Catalog.XYZ_Catalog:
                 XYZCtrl _XYZCtrl = new XYZCtrl(parent);
                 ctrl = _XYZCtrl;
                 break;

            case ...
        }
        return ctrl;
    }

    private void frmDesktop_Load(object sender, EventArgs e)
    {
        ...
        // load the user control into the panel
        activeCtrl = GetActiveUsrCtrl(catalogId, parent);
        pUserControlContainer.Controls.Add(activeCtrl);
        ...
    }

I'm trying to keep things simple and small so in “GetActiveUsrCtrl” I use an empty user control and assign my control to it.

This works and loads the desired user control into a panel, as expected.

The problem I'm having is calling the public methods of the control. Because of the way I loaded the user control, when I try to use reflection to invoke the method I get a NullReferenceException .

Bellow it's an example of the code I'm using:

Private void button1_Click(object sender, EventArgs e)
{
    Type tp = null;
    MethodInfo mtd = null;
    tp = hActiveUsrCtrl.GetType();
    mtd = tp.GetMethod("GetData");
    string Criteria = (mth.Invoke(hActiveUsrCtrl, null)).ToString();
}

Is what I'm trying here even possible?

Thanks.

Answer 1

Create an interface containing all your controls methods

public interface IMyControl
{
 public void clear();
 public string getastringvalue();
 etc......
}

Get all your controls to inherit from this interface:

public class MyControl : UserControl, IMyControl

Cast all your controls to the interface:

private void button1_Click(object sender, EventArgs e)
{
    IMyControl typedControl = hActiveUsrCtrl as IMyControl;
    typedControl.Clear();
    etc...
}

On a side not Reflection is inefficient and should be avoided where possible!

Answer 2

UserControls are implemented as classes, so you can have that class implement an interface, and just call the GetData method that way.

public interface IGetData {
  string GetData(parameters ...);
}

public class MyUserControl : UserControl, IGetData {
  ...
}

If all the User Controls can have the same signature for the GetData method, you don't even have to figure out which type it is, just cast it to IGetData.

IGetData getable = activeCtrl as IGetData;
if (getable != null) {
  var data = getable.GetData(...);
  // do stuff with data
} else {
  throw new ApplicationException("activeCtrl was null or didn't implement IGetData");
}

Update:

If I understand, it looks like you need an intermediate variable.

// newUc implements IGetData, not hActiveUsrCtrl
IGetData newUc = hActiveUsrCtrl.GetActiveUsrCtrl(pare‌​nt.appInfo.catalogId, parent);
pUserControlContainer.Controls.Add((Control)newUc);

var data = newUc.GetData(parameters ...);

Answer 3

If all control have the same public methods etc., why do you not use an interface?

You may implement a control factroy class ControlFactory.GetUserSelectionControl() . This method creates at runtime the best control matching the selection of the user. You can pass in an input of a kind to identify the best control. And all controls implement in your case the same interface. Then you can directly call the methods without reflection. But in the meantime you got already an example on how to implement the interfaces.

Answer 4

If all the user control have the same methods, declare an interface, inherit from it, and cast to the interface.

something along the lines of :

ascx.cs file :

public partial class AleaPoisson : UserControl, ISymboleAlea {
public void SomeFunction();
...
}

aspx.cs file :

( conteneur should be a PlaceHolder control and it should be loaded on Page_Init, rather than Page_Load if possible )

var ctl = conteneur.Page.LoadControl( path );
conteneur.Controls.Add( ctl );
((ISymboleAlea)ctl).SomeFunction();