Forum

C# Events in vvvv

vvvv beta question
#1

Hiya!
I wanna do a node which outputs Drag and Drop information about a window selected by a handle. I searched for it and I found very simple solutions like this http://www.jonasjohn.de/snippets/csharp/drag-and-drop-example.htm which was planned to be used for listboxes.
currently i only want a simple bang when DragEnter, DragDrop and DragLeave happens on that window and maybe i would like to retrieve the string what is dragged. Anyway I’ve only came to a mess which produces nothing but an “Object reference not set to an instance of an object.” exception. I’m suspicious that i’ve used “this”

window.DragEnter += new DragEventHandler(this.window_DragEnter);

in a wrong way. however if i say

window.DragEnter += new DragEventHandler(VVVV.Nodes.WindowsDragAndDropNode.window_DragEnter);

instead of “this” the compiler says
“An object reference is required for non-static field, method or property ‘VVVV.Nodes.WindowsDragAndDropNode.window_DragEnter(object, System.Windows.Forms.DragEventArgs)’”
however in all examples the method called on the event doesn’t have those “object” and “DragEventArgs” arguments in the DragEventHandler() just in the declaration so I don’t really understand where those two come from in the examples as well.
Anybody could help with this?

this is what i’m talking about (19.5 kB)

#2

the first line is good. but the window you are trying to cast to a form is null. i think you can only cast c# form windows like this.

the compiler tries to tell you that you have to provide a object method reference and not a static method reference.

if the window cast would work, the code could work like this:

code(lang=csharp):

  • region usings
    using System;
    using System.ComponentModel.Composition;
    using System.Windows.Forms;
    using System.Collections;

using VVVV.PluginInterfaces.V1;
using VVVV.PluginInterfaces.V2;
using VVVV.Utils.VColor;
using VVVV.Utils.VMath;

using VVVV.Core.Logging;

  • endregion usings

namespace VVVV.Nodes
{
#region PluginInfo
[PluginInfo(Name = “DragAndDrop”, Category = “Windows”, Help = “Basic template with one value in/out”, Tags = “”)](PluginInfo(Name = “DragAndDrop”, Category = “Windows”, Help = “Basic template with one value in/out”, Tags = “”))
#endregion PluginInfo
public class WindowsDragAndDropNode : IPluginEvaluate
{
#region fields & pins
[Input(“Window Handle”, DefaultValue = 0)](Input(“Window Handle”, DefaultValue = 0))
IDiffSpread FHandle;

  [Output("DragEnter")](Output("DragEnter"))
  ISpread<bool> FDragEnter;
  
  Control FWindow; //store the window so that it doesn't get garbage collected
  bool FDragEnterState;
  object FDragThreadLock = new object();

  [Import()](Import())
  ILogger FLogger;
  #endregion fields & pins

  //called when data for any output pin is requested
  public void Evaluate(int SpreadMax)
  {
  	FDragEnter.SliceCount = 1;
  	
  	if(FHandle.IsChanged)
  	{
  		IntPtr handle = new IntPtr(FHandle[0](0));
  		FWindow = (handle==IntPtr.Zero) ? null : Control.FromHandle(handle); //store window
  		
  		if(FWindow != null)
  		{
  			//do this only once
  			FWindow.DragEnter += new DragEventHandler(this.window_DragEnter);
  			FLogger.Log(LogType.Debug, "window is good");
  		}
  		else
  		{
  			FLogger.Log(LogType.Debug, "window of handle " + handle.ToInt64() + " is null, cast isn't working");
  		}
  	}
  	
  	lock(FDragThreadLock) //make sure that no other thread is changing the state while writing it
  	{
  		//write the state
  		FDragEnter[0](0) = FDragEnterState;
  		
  		//reset the state
  		FDragEnterState = false;
  	}

  }
  
  //this can happen at any time, so you have to store the state until the vvvv main loop can read it
  public void window_DragEnter(object sender, System.Windows.Forms.DragEventArgs e)
  {
  	lock(FDragThreadLock) //make sure vvvv is not writing the state while it gets changed
  	{
  		FDragEnterState = true;
  	}
  	
  	e.Effect = DragDropEffects.All;
  }

}
}

#3

aah thanks! I see now! well that’s a bad news. do you know another way to get drag’n’drop data about that renderer?
i found this: http://msdn.microsoft.com/en-us/library/windows/desktop/bb774303(v=vs.85).aspx but retrieving the info about the dropped file with “DragQueryFile” requires some pointer story i’m not really sure about in managed environment.

#4

i am sure you will find some answers here: http://stackoverflow.com/questions/2061167/how-to-receive-the-windows-messages-without-a-windows-form

or here:
http://www.codeproject.com/Articles/3946/Trapping-windows-messages

#5

hmm that’s some kind of low-level network communication method it seems to have nothing to do with window messages

#6

it was using the same terms, probably the same api, but check the new links. maybe they help…?

#7

that message trapping seems useful. i’ve tried GetMessage with DLLImport from user32.dll but that freezed vvvv. I’ll give that a try!

edit: maaan this is a disaster. i’ll just create a separate form for dropping files:D

© vvvv group