Re: sharing an event handler, not getting what I expect - C# Discussion Boards

sharing an event handler, not getting what I expect

1-Oct-07 5:14

If you are only looking to extend the Windows Explorer then you can check out Shell namespace extensions: here[^] and this commerical product[^].

Take care,
Tom

-----------------------------------------------
Check out my blog at http://tjoe.wordpress.com

JoeRip1-Oct-07 3:47

Re: sharing an event handler, not getting what I expect

1-Oct-07 3:47

In my code I create three combo boxes, and store them in an ArrayList. So:

myArrayList.Insert(0, new System.Windows.Forms.ComboBox());<br />
myArrayList.Insert(1, new System.Windows.Forms.ComboBox());<br />
myArrayList.Insert(2, new System.Windows.Forms.ComboBox());

I then add each of these comboboxes to my form; at the same time, I bind each of them to a shared data source and a shared event handler:

<br />
myForm.Controls.Add((ComboBox)myArrayList[0]);<br />
((ComboBox)myArrayList[0]).DataSource = aComparisonList_Strings;<br />
((ComboBox)myArrayList[0]).SelectedIndexChanged += new EventHandler(cmbComparison_SelectedIndexChanged);<br />
<br />
myForm.Controls.Add((ComboBox)myArrayList[1]);<br />
((ComboBox)myArrayList[1]).DataSource = aComparisonList_Strings;<br />
((ComboBox)myArrayList[1]).SelectedIndexChanged += new EventHandler(cmbComparison_SelectedIndexChanged);<br />
<br />
myForm.Controls.Add((ComboBox)myArrayList[2]);<br />
((ComboBox)myArrayList[2]).DataSource = aComparisonList_Strings;<br />
((ComboBox)myArrayList[2]).SelectedIndexChanged += new EventHandler(cmbComparison_SelectedIndexChanged);<br />

When the user chooses an item in the first combo box control, the SelectedIndex changes for ALL THREE CONTROLS. That's not what I want; I just want the three controls to share a datasource and an event handler. What am I doing wrong?

TJoe1-Oct-07 3:57

Re: sharing an event handler, not getting what I expect

1-Oct-07 3:57

I don't think you will be able to share the data source like that. I believe datasources have a single "current record", which all the combo boxes are going to show. So if you change one, then the others will reflect that change also. This is typically the desired behavior.

What is the type of your data source? You may be able to Clone it to get around this problem.

Take care,
Tom

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Check out my blog at http://tjoe.wordpress.com

JoeRip1-Oct-07 4:02

Re: sharing an event handler, not getting what I expect

1-Oct-07 4:02

Ah! Thank god I included the DataSource in the sample code, I didn't expect that to be the source of the problem. I would have never checked that.

The DataSource is an ArrayList with string to show in the drop down. It's not dynamic, so I can keep it anywhere, and it's short, so I can actually just generate it on the fly and assign it. That's inefficient, I know, and if I have 100 comboboxes, I'll have 100 arrays of the same 10 strings around, but I can live with that.

Let me go test your theory. Great catch, there.

JoeRip1-Oct-07 4:15

Re: sharing an event handler, not getting what I expect

1-Oct-07 4:15

Yep, that was it. I should have figured this out, since none of the other controls which were sharing handlers were showing similar behavior (buttons, checkboxes, etc), EXCEPT the other controls that had DataSources.

A couple of the comboboxes do have lengthy lists attached to them. You're saying I should CLONE my original array, and bind to that? Is that any more efficient that just looping through the original array, using combo.items.add to add it to each combo as I create it?

TJoe1-Oct-07 4:30

Re: sharing an event handler, not getting what I expect

1-Oct-07 4:30

I'm not sure it matters. Any way you look at it, you will have to have three (assuming there are three ComboBoxes) lists. There are either three DataSources or three ComboBox.Items.

If the lists are long you may want to create a wrapper around the ArrayList. The wrapper would take a reference to an ArrayList. It would also implement the IList (and possibly the IList<T>) interface. Then you could just forward the IList method calls to the wrapped ArrayList. This way you have a small (in terms of memory) object that "points" to the large ArrayList. Then you would create three instances of your wrapper (all pointing to the same ArrayList). I believe this will get around the DataSource issue. This is really only useful if your ArrayList is large, since it would reduce memory usage.

Take care,
Tom

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Check out my blog at http://tjoe.wordpress.com

Luc Pattyn1-Oct-07 4:35

Re: sharing an event handler, not getting what I expect

1-Oct-07 4:35

Hi,

AFAIK you can share an array, ArrayList, List, ... between multiple ComboBoxes;
these collections don't have a "current selection" that they would impose on the ComboBoxes.
So I see no need to Clone() anything.

Smile | :)

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JoeRip1-Oct-07 4:41

Re: sharing an event handler, not getting what I expect

1-Oct-07 4:41

I'm not sure what you mean by "sharing" the Collection here. Aside from binding the Collection to the Combo as a DataSource (which I was doing earlier, and that was causing the problem), or copying the individual items from the Collection to the combo one at a time, what other method are you talking about to attach to the Collection to the combo?

Luc Pattyn1-Oct-07 5:49

Re: sharing an event handler, not getting what I expect

1-Oct-07 5:49

Hi,

if you assign the same array/ArrayList/List as the DataSource of several ComboBoxes,
how would they exchange current selection info Confused | :confused:

They don't!

Smile | :)

Luc Pattyn [Forum Guidelines] [My Articles]

TJoe1-Oct-07 5:56

Re: sharing an event handler, not getting what I expect

1-Oct-07 5:56

I think the BindingContext[^] on the form maintains it for each DataSource. Since each ComboBox has the same data source (e.g. ReferenceEquals would return true), then they all share the same "current record" (which is maintained by the BindingContext. Apparently, you can "group" data bound controls using Panels (or GroupBox, etc) but you have to set the BindingContext property on the Panel to override the Form's BindingContext.

Take care,
Tom

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Check out my blog at http://tjoe.wordpress.com

JoeRip1-Oct-07 5:57

Re: sharing an event handler, not getting what I expect [modified]

1-Oct-07 5:57

Well, Luc, try it out Smile | :)

.

The whole point of binding DataSources is to share the Binding Context, so that all of the controls point at the same "record" in the DataSource. That way you can have several controls on the form (like, say, Back/Forward/Edit/Delete, etc) that all deal with the same "row" or data in the source.

I had completely forgotten about this when I used "combo.DataSource = myArray". I was just looking for a cheap way to make all of the items in my array show up in the combo box.

TJoe is right, if I want each combo to have its own context to the data in my array, I need to either Clone each array and bind to it, or just copy the items from the array to the combo.Items collection manually.

Since there is no real advantage to making the array a DataSource here (I'm not really using the BindingContext for what its intended), I'm just doing the latter now.

Luc Pattyn1-Oct-07 6:03

Re: sharing an event handler, not getting what I expect

1-Oct-07 6:03

JoeRip wrote:
try it out

OK, I'll add it on the todo list (not at the top though).

[added] checked. You're right, ComboBoxes sharing a DataSource, even a simple array,
become fully synchronized. I didn't know that. Thanks.[/added]

Smile | :)

-- modified at 12:24 Monday 1st October, 2007

Luc Pattyn [Forum Guidelines] [My Articles]

TJoe1-Oct-07 4:50

1-Oct-07 4:50

The collection object themselves do not maintain the current record. I believe the ComboBox and other controls maintain it. Specifically, the BindingContext[^]. It looks like if you add the ComboBoxes to a Panel, then that would create a new BindingContext.

Take care,
Tom

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Check out my blog at http://tjoe.wordpress.com

Problem with macros

yadlaprasad1-Oct-07 3:29

yadlaprasad

1-Oct-07 3:29

Hi all,

I am working with Visual studio Macros.
I created one macro.and i assigned one keyboard shortcut to run that macro in VS 2005 Applications.its wrkng fine.

But my problem is when i taken new application when i wrk wth this shortcut macro is not firing.

So,to make macros global to all applications what to do?

krishna Prasad

fttyhtrhyfytrytrysetyetytesystryrty

Re: Problem with macros

TJoe1-Oct-07 3:48

help with code to implement a calculator....

1-Oct-07 3:48

I believe you need to restart VS after assigning the shortcut. Basically, VS saves changes when it exits. So if you open VS, assign the shortcut, then open another instance of VS then the second instance will not have the assigned shortcut. This is typical of most settings in VS.

Take care,
Tom

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Check out my blog at http://tjoe.wordpress.com

MinhajuddinK1-Oct-07 3:25

MinhajuddinK

1-Oct-07 3:25

Hi all,

I am new to C#....

I thought that implementing a simple calculator would help me understand the language... I have come up with a code....

It would be great if the gurus here give me feedback on this...

<br />
using System;<br />
using System.Collections.Generic;<br />
using System.Text;<br />
<br />
namespace Calculator<br />
{<br />
    class compute<br />
    {<br />
        private string[] inputNumbers;<br />
        public string computeResult(string inputExpression)<br />
        {<br />
            string result = "There was an error while processing!";<br />
            inputExpression = inputExpression.Replace("+", "+A");<br />
            inputExpression = inputExpression.Replace("-", "-S");<br />
            inputExpression = inputExpression.Replace("*", "-M");<br />
            inputExpression = inputExpression.Replace("/", "/D");<br />
<br />
            if (inputExpression.Substring(0, 1) != "-" && inputExpression.Substring(0, 1) != "+")<br />
                inputExpression = "A" + inputExpression;<br />
            else<br />
                inputExpression = inputExpression.Substring(1);<br />
            inputNumbers = inputExpression.Split('+', '-', '*', '/');<br />
<br />
            decimal output=0;<br />
            int i;<br />
            int count = inputNumbers.Length;<br />
            for (i = 0; i < count; i++)<br />
            {<br />
                string calc = "";<br />
                inputNumbers[i] = inputNumbers[i].Trim();<br />
                decimal temp;<br />
                if (!decimal.TryParse(inputNumbers[i].Substring(1),out temp))<br />
                    break;<br />
                calc = inputNumbers[i].Substring(0,1);<br />
<br />
                switch(calc)<br />
                {<br />
                    case "A":<br />
                        output = output + temp;<br />
                        break;<br />
                    case "S":<br />
                        output = output - temp;<br />
                        break;<br />
                    case "M":<br />
                        output = output * temp;<br />
                        break;<br />
                    case "D":<br />
                        output = output / temp;<br />
                        break;<br />
                }<br />
<br />
                <br />
            }<br />
            <br />
            if(i==count)<br />
                result = output.ToString();<br />
            return result;<br />
        }<br />
    }<br />
}<br />
<br />

You don't have to be ~~AFRAID!~~

Re: help with code to implement a calculator....

led mike1-Oct-07 4:43

led mike

1-Oct-07 4:43

Minhaj.Net wrote:
I have come up with a code....

It would be great if the gurus here give me feedback on this...

Yes that does appear to be code

Did you read the first message in the forum titled, "How to get an answer to your question"?

Re: help with code to implement a calculator....

Luc Pattyn1-Oct-07 4:55