Chapter 27-3 column

Mark P. · June 30th, 2011, 02:30 PM

I'm working through the Chapter 27 exercises, and on 3. what are the Items settings that define the data for the ListView columns? I can't seem to find a reference to this. thanks again for all your help.

Rod Stephens · June 30th, 2011, 04:12 PM

Do you mean how does the program set the item values or how does it prepare the ListView to hold them? The ListView control is pretty useful but it's a bit awkward to use.

To prepare the control at design time, select the control and select its Columns property. Click the ellipsis on the right to open the ColumnHeader Collection Editor. Use it to make the columns.

To create items at design time, select the Items property and click the ellipsis on the right. Add an item and set its Text. Then click the SubItems property (in the Data section) and click its ellipsis. There you can add the sub-item values.

To create an item at run time, you add it to the Items collection. that collection's Add method returns a new ListViewItem. You then add the sub-items to that object's SubItems collection. I use the following method to make this easier.

Code:

// Make a row in the ListView.
private void MakeCar(string name, int maxSpeed, int horsepower, decimal price)
{
    ListViewItem item = carListView.Items.Add(name);
    item.SubItems.Add(maxSpeed.ToString());
    item.SubItems.Add(horsepower.ToString());
    item.SubItems.Add(price.ToString("C"));
}

I hope that helps. If I've missed your question, let me know.

Mark P. · June 30th, 2011, 04:32 PM

No, you are on track with your answer. The question I have is regarding the syntax of the appropriate fields within Items and SubItems. So, in the Items property, the text is entered similar to the name of the column? And with the subitem, Data section, the actual name of the object is entered, maxspeed, horsepower?

Rod Stephens · June 30th, 2011, 04:55 PM

Well, normally your code can access the items and sub-items by index. You can't say listView1.Items["FirstName"] = "Rod" or whatever. Instead you need to add a new item using Items.Add and then use the returned object;s SubItems.Add method to add the subitems. It's a bit awkward.

Each of the items and sub-items has a Name property that you can set and then later use to find an item. For example, this code sets the first item's Name to "A":

listView1.Items[0].Name = "A";

Now you can refer to it like this:

Console.WriteLine(listView1.Items["A"].Text);

Similarly you can set and get a sub-item's Name:

listView1.Items["A"].SubItems[0].Name = "Test";
Console.WriteLine(listView1.Items["A"].SubItems["Test"].Text);

Oddly at design time the Items collection editor doesn't support the Name property and the SubItems collection editor seems to display it but doesn't seem to store the values you enter for use at run time so they aren't very useful unless you populate the values at design time.

You can take other approaches. For example, you can assign names to the columns and then look in the Columns collection to see their names. Similarly you can look at a column's Text property to see what it says. Once you find the column you want, you may be able to use its index to access sub-items.

As I said before, it's a bit awkward.

Do you have a particular scenario in mind?

Mark P. · June 30th, 2011, 05:06 PM

Okay, I think I may have sent you off in a wrong direction. I'm referring to configuring the columns using the Properties of Listview box for the Form1.cs[Design]. I built the form, but when I click on the columns they aren't sorting. I suspect I have the control properties set incorrectly.

Rod Stephens · June 30th, 2011, 05:32 PM

I think I see. The sorter class for those exercises can look at the items' subitems. For example:

if (item1.SubItems[0].Text < item2.SubItems[0].Text) ...

You'll want to use different indexes in the array depending on which column you are using to sort. I.e. instead of [0] you may want to use [1] or [2] or [SortColumn] where SortColumn is a property that tells you which column to use in sorting. I think the ColumnClicked event handler has a parameter that tells you which column was clicked.

Let me know if I'm still headed in the wrong direction. (And remember you can download the solution and peek if you need to.)

Mark P. · June 30th, 2011, 06:36 PM

I'd gladly take a peek. For some reason, Designer mode for the form isn't an option under View when I download the book's version of the project.

Mark P. · July 1st, 2011, 05:04 PM

Well, I figured it out. For the repetitive lines of code, I have been copying and pasting sections like this
CarComparer sorter = new CarComparer(CarComparer.SortType.ByMaxSpeed);
List<Car> sortedCars = new List<Car>(Cars);
sortedCars.Sort(sorter);
carListBox.DataSource = sortedCars;

And then changing the variables. It looks like Visual Studio is a little more finicky about recognizing code entered this way than I expected. Once I re-entered some of the variables, the columns sorted. thanks for your help again.