Re: Some questions regarding ListView fundamental behaviour - C# Discussion Boards

You're creating UI controls on a background thread that is MTA apartment state. That's a no-no, and will cause issues.

Before starting your thread, call

th.SetApartmentState(ApartmentState.STA);

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Judah Himango

Hi -- Thank you for your response. I added what you suggested, yet the splash screen still sticks around until you click in the main window. Any other ideas?

Thank you kindly,

Glenn

I have a project which works with it's own special files - *.gdraw.
I want to make the program when a *.gdraw file is double clicked to be loaded in the program. How is this done?
...
I read some articles and learned that i need the command line arguments. static void Main(string[] args)
{
Application.EnableVisualStyles();
Application.SetCompatibleTextRenderingDefault(false);
Application.Run(new MainForm(args));
}
This is the code in the Program.cs. But it doesn't seem to work.

modified on Sunday, March 9, 2008 2:26 PM

Here you go: Registering the Extension[^]

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Hi all,

Whenever my ListView (let's call it ListView1) selected IDX changes, I wish to grant focus to another ListView (let's call it ListView2), but this is a bit problematic:

If I write ListView2.Focus() inside the ListView1.SelectedIndexChanged event handler, ListView1 is focused. In order to explain this behaviour, I'll mention few facts:

1. Mouse click is composed of 2 events: MouseUp and MouseDown. in each of these cases the control receives focus, if he didn't have it already.

2. whenever changing the selected line at a ListView, the event SelectedIndexChanged is called twice: once for removing the selection from the previously selected line, and once for selecting the new line.

So, the flow is as followed:

1. starting point: line 1 is selected in ListView1.
2. I'm clicking line 2 of ListView1.
3. Line 1 of ListView1 is unselected, which causes firing the event SelectedIndexChanged of ListView1. Now ListView2 receives focus.
4. Line 2 of ListView1 is unselected, which causes firing the event SelectedIndexChanged of ListView1. ListView2 already has focus.
5. Now ListView1 receives focus, since the MouseUp event (fired due to the MouseClick event).

Does anyone have a solution for focusing a control when changing a ListView selected IDX? it also bothers (due to other reasons) that the event SelectedIndexChanged is fired twice for each line selection. Verifying this behaviour can be done by using:

private void listView1_SelectedIndexChanged(object sender, EventArgs e)<br />
{<br />
     System.Threading.Thread.Sleep(500);<br />
     System.Media.SystemSounds.Beep.Play();<br />
}

When you'll change the selected line, 2 beeps will be heard.

Thanks and sorry for the long question!

Eyal.

I've always found the ListView to be a very quirky control to work with. The biggest question to answer is why are you using it?
If possible, you should work around it by getting rid of the listview and go with the ListBox instead. Also you want to avoid what you do with events.

You can call SuspendLayout() (I THINK) you will have to verify in the method description. Basically it suspends the events when changing things around in the control.

You can also minimize issues by avoiding too many events. SelectedIndexChange is a good one to get yourself into a hung state just by having one control change another control and having both of them trigger off the change event.

In my test I had the selected index change load the second listview with items. I failed to give it focus as well....but I found that I only had the event fire once!

You probably get only one SelectedIndexChanged event fired since no item was selected prior to your selection. If an item is selected and then you select different item, the event is fired twice: once for unselecting the first item and once for selecting the second item.

I'll try using the SuspendLayout() function as you suggested and see if it can help.

As for using ListBox - what makes it better? Doesn't it have less functionality than ListView? I'm using ListView since every item in my application is composed of multiple columns.

Thanks a lot for your help!

Eyal.

modified on Tuesday, March 11, 2008 4:28 AM

WRONG.

I get only one event fired because only one event firing happens when an event gets selected. There is no such thing as an event getting fired twice because the control is 'unslecting the first item' unless you have written some code that issues the event. Regardless of how many times I did the selection, I got only one event. The only time you get multiple events fired is because you've written some bad code that is causing the multiple events to fire. Are you calling an event like Select()? Are you programattically doing something to try and change a selection? Are you bound to other events such as losing focus, our MouseLeave, or anything like that? Are you manually setting focus to something when you shouldn't?

No matter how frequently I select an item there is always only one event that is fired. That is the event model in Windows -- not something I've done. The field getting 'unselected'? That is not a seperate event unless you bind yourself to the lost focus event (or some such stupid thing as that)

In a Windows Form application the ListBox is far more flexible. You can put any object into the list. You control what is displayed by handling the ToString event. The ListView can only have ListViewItem objects in it. So from that aspect of it the ListView is pitiful.

This is the totallity of my code and I get only one event each time I select a new item no matter how many times I do it in a row. And it would be extremely amateurish of me to say I'm getting only one event if I had not done multiple selects in a row. So keep your insults to yourself.

public partial class Form1 : Form
{
    public Form1()
    {
        InitializeComponent();
    }

    private void listView1_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (listView1.SelectedIndices.Count.Equals(0)) return;

        if (listView1.SelectedItems[0].Text.Equals("Fish"))
            LoadFish();
        else
            LoadMammals();
    }

    private void LoadMammals()
    {
        listView2.Items.Clear();
        listView2.Items.Add(new ListViewItem("Horse"));
        listView2.Items.Add(new ListViewItem("Human"));
        listView2.Focus();
    }

    private void LoadFish()
    {
        listView2.Items.Clear();
        listView2.Items.Add(new ListViewItem("Mantaray"));
        listView2.Items.Add(new ListViewItem("Lion Fish"));
        listView2.Focus();
    }

}

OK,

So I've created a new project which has only one ListView with two items, and one event hadler - for SelectedIndexChanged event. Here is the code:

namespace TestListViewSelectedIndexChanged<br />
{<br />
    public partial class Form1 : Form<br />
    {<br />
        public Form1()<br />
        {<br />
            InitializeComponent();<br />
        }<br />
<br />
        private void listView1_SelectedIndexChanged(object sender, EventArgs e)<br />
        {<br />
            System.Threading.Thread.Sleep(500);<br />
            System.Media.SystemSounds.Beep.Play();<br />
        }<br />
    }<br />
}

The Sleep is ment to hear both beeps.
Now, whenever I select item, 2 beeps are heard. What's the explanation for this behaviour if the event only fired once?

Pleae note that I do not suspect your knowledge, I'm sure it's bigger than mine. I just want to understand this phenomenon.

Thanks,

Eyal.

Hi All,

Here's in interesting one. If you have a Dictionary like:

String1, 0
String2, 0
String3, 10
String4, 20

How do you locate the key(String4) based on the fact that it has the highest int value (20)?

Thanks,

Jammer

Going where everyone here has gone before! Smile | :)

Some C# 3 goodness:

string stringWithHighestIntValue = dictionary.OrderBy(input => input.Value).Last().Key;

Genius!!

I so love generics!!! Thanks professor!

Jammer

Going where everyone here has gone before! Smile | :)

Keep in mind the good professor's solution will throw an exception if the dictionary is empty, see the Last() extension method[^] used there. You may want to tweak that code a tad to account for empty dictionaries.

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Judah Himango

Ok, I'm stuck on something else with this dictionary malarky now. Once I've done an evaluation and worked out the highest value in my dictionary and grabbed the string I need to reset all the values in the dictionary to zero.

I'm getting errors at the moment saying that the collection has been modified and that it can't enumerate over the collection. So far I've tried:

Dictionary<string, int="">.KeyCollection keycoll = FileScore.Keys;
foreach (string s in keycoll)
{
    FileScore[s] = 0;
}</string,>

Which fails on the second loop ...

and I've tried:

foreach (KeyValuePair<string, int=""> kvp in FileScore)
{
    FileScore[kvp.Key] = 0;
}</string,>

How am I going to get around this problem of reinitialising the dictionary to hold all zero values?

Jammer

Going where everyone here has gone before! Smile | :)

Yeah, you can't modify a collection while iterating over it; kind of a chicken-and-egg problem.

One easy solution is to iterate over a copy the collection and modify the original:

            foreach (var item in dictionary.ToArray()) // iterate over a copy of the collection
            {
                dictionary[item.Key] = 0;
            }

Tech, life, family, faith: Give me a visit.
I'm currently blogging about: Upon this disciple I'll build my new religion?
The apostle Paul, modernly speaking: Epistles of Paul

Judah Himango

That is a bit of a bind isn't it ... I'm just rewriting my code with no dictionary. I'm trying to shoehorn functionality out of the wrong approach basically ...

I've just defined a new collection and I'm going to use a List<t> instead. I'm sure I'll find some problems along the way Smile | :)

Jammer

Going where everyone here has gone before! Smile | :)

After some futzing around i'm going to do this I think. I'm performing this each time:

Dictionary<string, int> FileScoreCopy = new Dictionary<string, int>(FileScore);

Just out of interest. How do you 'delete' this FileScoreCopy once your done with it? I guess some form of proactive garbage collection.

Jammer

Going where everyone here has gone before! Smile | :)

You don't delete it. When it goes out of scope, it automatically becomes eligible for garbage collection. The .NET garbage collector will reclaim the memory reserved for this object when it runs in the background.

Tech, life, family, faith: Give me a visit.
I'm currently blogging about: "Religion of Peace" Strikes Jerusalem
The apostle Paul, modernly speaking: Epistles of Paul

Judah Himango

OK. I need to look into what a destructor is then as that's what I thought they were for.

Thanks,

Jammer

Going where everyone here has gone before! Smile | :)

Nope, a destructor is only required if you're dealing with unmanaged resources (e.g. closing Win32 files, closing database connections, etc.). For regular managed code where you're not dealing with unmanaged resources, you don't need to implement a destructor.

Tech, life, family, faith: Give me a visit.
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The apostle Paul, modernly speaking: Epistles of Paul

Judah Himango

Ahhhhhh, that makes total sense now.

I was reading about the generations in the GC the other day ... all very interesting! Much to learn!

Jammer

Going where everyone here has gone before! Smile | :)

Hi i had a discussion with my friend about OOP and now i want to ask some of you.
The question is:

Knows a file how it can be printed or knows a printer how it can print a file ?

or

Knows a car how it can be repaired or knows a car repair shop how it can repair a car?

or

Knows a clothes how it can be washed or knows a washmaschine how it can wash a clothes

or generally

when have a class a specific ability on its own and
when have only another class a specific ability and need another class to do it

according to a example above:

File.Print( ) or Printer.Print( File ) ?

Car.Repair( ) or CarRepairShop.Repair( Car ) ?

Clothes.Wash( ) or WashMaschine.Wash( Clothes ) ?

MarkPhB wrote:
File.Print( ) or Printer.Print( File ) ?

Car.Repair( ) or CarRepairShop.Repair( Car ) ?

Clothes.Wash( ) or WashMaschine.Wash( Clothes ) ?

My opinion:

- neither, usually a printer doesn't care about the document being sent to him, you'd have to convert any object (file, bitmap, text) to a format the printer can actually print (raw bitmap e.g.)
- CarRepairShop.Repair( Car )
- WashMaschine.Wash( Clothes )

Objects like files, cars, clothes etc. have some properties on their own, but they usually don't have any abilities. A car probably doesn't know how to repair itself, but due to some given properties it may know how it should be accelerated, so Car.Accelerate() might be okay in some circumstances.

regards

modified 12-Sep-18 21:01pm.

yea thats my opinion too

but my friend say: "Only the class knows what it can be done with it"

for his example: "An object knows how it can be saved in a database".

So he means: Object.Save() and not Database.Save( Object )

Then you, me and the .NET framework disagree with your friend Wink | ;)

Object.Save() makes no sense because where should the object save itself to? A database connection, a file system, over network? The object doesn't know about either of the available streams.
Also, saving an object depends on the place being stored to. For a database it would be a SQLConnection, for the hard disk it would be a FileStream, for network a NetworkStream. So only the streams themselves know how to execute the proper Save() operation.

modified 12-Sep-18 21:01pm.