[RESOLVED] Invoke RichTextBox From Another Thread

Hello, I modified some code I found after a search on google. The original code was written my jmc. It originally, on the original code, a void. I tried to modify it to work with a string[].

I am currently getting a Parameter count error message.

Code:

private delegate string[] GetRtbSongsLinesDelegate(object item); private string[] GetRtbSongsLines(object item) { if (this.rtbSongs.InvokeRequired) { // This is a worker thread so delegate the task. this.rtbSongs.Invoke(new GetRtbSongsLinesDelegate(this.GetRtbSongsLines),null); } else { // This is the UI thread so perform the task. return this.rtbSongs.Lines; } return null; }

I am calling this using:

Code:

GetRtbSongsLines(null)

For example:

Code:

if(GetRtbSongsLines(null).length > 0){ //There are more than 0 lines }

What's wrong?

Re: Invoke RichTextBox From Another Thread

At which line do you ge the error?

Re: Invoke RichTextBox From Another Thread

Code:

this.rtbSongs.Invoke(new GetRtbSongsLinesDelegate(this.GetRtbSongsLines),null);

Re: Invoke RichTextBox From Another Thread

I address this specifically in my Accessing Controls From Worker Threads thread in the CodeBank. Go and read post #3 of that thread, which specifically deals with returning data across thread boundaries.

Re: Invoke RichTextBox From Another Thread

Using your example for passing in a control as the parameter, could I essentially return the actual control instead of the text of the control and then use the returned control to access its different members/properties?

Using those principals here is a method that returns the actual control - will this work, or is there some reason why this isn't used instead of more specific methods?

Code:

private delegate string GetControlTextInvoker(Control ctl); private string GetControlText(Control ctl) { string text; if (ctl.InvokeRequired) { text = (string)ctl.Invoke(new GetControlTextInvoker(GetControlText),ctl); } else { text = ctl.Text; } return text; }

Re: Invoke RichTextBox From Another Thread

The whole point of this delegation is that you can NOT access members of a control directly unless you're on the thread that created it. There's no point returning a control because you can;t then access it's members.

The reason I created that CodeBank thread in the first place was to provide a simple set of steps that anyone could follow and get delegation to work. Far too many people don't want to follow the steps though. They just jump to the end and wonder why it won't work. Follow the steps as they apply to your specific scenario and it will work. Here's post #3 from the CodeBank reposted but with code appropriate to your situation. This is how easy it is if you do as instructed and follow the steps provided.
Quote:
Originally Posted by jmcilhinney
Getting a return value is no more difficult. One thing I haven't mentioned is that the Invoke method is a function. If the method invoked by the delegate returns a value then that is propagated by the Invoke method. Let's use an example of getting the Text property of a TextBox. Following the steps laid out already we first create a method to do the job:
CSharp Code:
private string[] GetRichTextBoxLines()
{
    return this.rtbSongs.Lines;
}
Next we declare a matching delegate:
CSharp Code:
private delegate string[] GetRichTextBoxLinesInvoker();
 
private string[] GetRichTextBoxLines()
{
    return this.rtbSongs.Lines;
}
After that we test the InvokeRequired property:
CSharp Code:
private delegate string[] GetRichTextBoxLinesInvoker();
 
private string[] GetRichTextBoxLines()
{
    if (this.rtbSongs.InvokeRequired)
    {
 
    }
    else
    {
        return this.rtbSongs.Lines;
    }
}
Finally we call the Invoke method and pass an instance of our delegate:
CSharp Code:
private delegate string[] GetRichTextBoxLinesInvoker();
 
private string[] GetRichTextBoxLines()
{
    if (this.rtbSongs.InvokeRequired)
    {
        return (string[])this.rtbSongs.Invoke(new GetRichTextBoxLinesInvoker(GetRichTextBoxLines));
    }
    else
    {
        return this.rtbSongs.Lines;
    }
}
Let's clean that up a little so we only have one Return statement, which is widely considered to be best practice:
CSharp Code:
private delegate string[] GetRichTextBoxLinesInvoker();
 
private string[] GetRichTextBoxLines()
{
    string[] lines;
 
    if (this.rtbSongs.InvokeRequired)
    {
        lines = (string[])this.rtbSongs.Invoke(new GetRichTextBoxLinesInvoker(GetRichTextBoxLines));
    }
    else
    {
        lines = this.rtbSongs.Lines;
    }
 
    return lines;
}
Notice that in this case we are actually returning the result of the Invoke method, which is the same value as was returned by the method that was invoked. This is how you get a value back onto your worker thread from the UI thread.

Notice also that the return value from the invoke method must be cast as the appropriate type. Invoke can be used to invoke any method at all, so it could return any value at all. That means that its actual return type is Object. You must therefore cast each returned object as its actual type.

Now to show that this method can be generalised to any control too, as well as combine the passing of parameters and returning a value, here's an extended example based on what we've already seen:
CSharp Code:
private delegate string[] GetTextBoxLinesInvoker(TextBoxBase ctl);
 
private string[] GetTextBoxLines(TextBoxBase ctl)
{
    string[] lines;
 
    if (ctl.InvokeRequired)
    {
        lines = (string[])ctl.Invoke(new GetTextBoxLinesInvoker(GetTextBoxLines),
                                     ctl);
    }
    else
    {
        lines = ctl.Lines;
    }
 
    return lines;
}

Re: Invoke RichTextBox From Another Thread

Thank you.

I am getting this error message:

Quote:

Object of type 'System.String' cannot be converted to type 'System.String[]'.

I don't see where I am converting a String to String array.. I am using strictly string arrays.

Here is the code:

Code:

private delegate void SetRtbSongsDelegate(string[] newLines); private void SetRtbSongs(string[] newLines) { if (this.rtbSongs.InvokeRequired) { // This is a worker thread so delegate the task. this.rtbSongs.Invoke(new SetRtbSongsDelegate(this.SetRtbSongs), newLines); } else { // This is the UI thread so perform the task. this.rtbSongs.Lines = newLines; } }

This is the line with the error:

Code:

this.rtbSongs.Invoke(new SetRtbSongsDelegate(this.SetRtbSongs), newLines);

I am calling this like so:

Code:

SetRtbSongs(new string[1] { "" });

Re: Invoke RichTextBox From Another Thread

The problem is the fact that Invoke is declared such that it takes a delegate and then a paramarray of arguments for the method being invoked. Your string array is being interpreted as multiple individual arguments rather than a single array argument. Try casting the array as type Object to force it to be interpreted as a single argument:

Code:

this.rtbSongs.Invoke(new SetRtbSongsDelegate(this.SetRtbSongs), (object)newLines);

Re: [RESOLVED] Invoke RichTextBox From Another Thread

It works!

Thanks & Resolved :check:

-Also your explanations of cross-threading and invoking are excellent!