Software Design Using C++

Second Advanced Windows Forms Example

The Plan

Getting Started

Adjusting the Controls

Make sure that the ListView control is selected and go to the Properties Window. Change the name to RootListView. Change the BackColor (background color) to a light yellow. If necessary, click the + sign in front of the Font property so that you can see all of the items listed within it. Set Bold to True. That's the only change to the Font property, so you can click on the - sign and collapse that stuff to a single line. Next, change the ForeColor to a bright blue. For the app in the pictures above, the ActiveCaption color found under System was used. Make sure that the GridLines property is set to True. That puts in vertical lines to separate columns and horizontal lines to separate the rows. Make sure that the Scrollable property is True, though it should be so by default. We want the user to be able to scroll through the list of roots. The View property should be set to Details (and not to SmallIcon or one of the other choices).

Save all of your files. Also right click on the new project in Solution Explorer and set this project to be the startup project.

Code for the First Improvement

System::Void Form1::StartButton_Click(System::Object * sender, System::EventArgs * e)
   {
   long k, Count;
   double Root;
   ListViewItem * Item;

   RootListView->Clear();
   RootListView->Columns->Add(S"Number", 64, HorizontalAlignment::Right);
   RootListView->Columns->Add(S"Root", 196, HorizontalAlignment::Right);
   Count = NumberBox->Text->ToInt32(NULL);

   for (k = 1; k <= Count; k++)
      {
      Root = Math::Sqrt(k);
      Item = new ListViewItem(k.ToString());
      Item->SubItems->Add(Root.ToString());
      RootListView->Items->Add(Item);
      }
   }

Notice that we set up Item as a pointer to a ListViewItem, the type of thing that we can put into our ListView. You might want to name this variable ItemPtr if you need a reminder that it is a pointer to an object and not the object itself. The essential thing that we do with this Item variable is to point it to a new object containing one row of data and then add that object to the Items collection of RootListView.

However, before we get to the details of that, we first clear any old data out of RootListView. Then we add the headings for our two columns. Recall that S"Number" is a way to create a string literal. Thus Number is the first heading. The heading is aligned to the right inside of a field 64 pixels wide. The second heading is set up in a similar way. It is also possible to set up the column headings by using the Properties Window with the ListView control. For further information use Help, Search and enter ListView.

The structure of the loop is similar to that of our old application. However, once we have a new value of k, we convert it to a string and stick it in a new ListViewItem object and have Item point to that object. You might wonder what SubItems refers to. These are items that get displayed (at least in Details view) to the right of the main item (the value of k) for each line. Thus we add the computed square root here. Finally, now that we have built up the desired ListViewItem, we add it to our ListView control. It makes sense once you try it out!

At this point it would be best to save all of your files. Then build and run your application to see that it works reasonably. The running app should look like the one shown in this picture.

Code for the Second Improvement

#pragma once

   #using <mscorlib.dll>   // added for NumberFormatInfo

namespace Roots2
{
   using namespace System;
   using namespace System::ComponentModel;
   using namespace System::Collections;
   using namespace System::Windows::Forms;
   using namespace System::Data;
   using namespace System::Drawing;
   using namespace System::Globalization;  // added for NumberFormatInfo

Then, in Form1.cpp revise the code for our click handler as follows:

System::Void Form1::StartButton_Click(System::Object * sender, System::EventArgs * e)
   {
   long k, Count;
   double Root;
   ListViewItem * Item;

   RootListView->Clear();
   RootListView->Columns->Add(S"Number", 64, HorizontalAlignment::Right);
   RootListView->Columns->Add(S"Root", 196, HorizontalAlignment::Right);
   Count = NumberBox->Text->ToInt32(NULL);

   CultureInfo * MyCI = new CultureInfo(S"en-US", false);
   NumberFormatInfo * nfi = MyCI->NumberFormat;
   nfi -> NumberDecimalDigits = 12;

   for (k = 1; k <= Count; k++)
      {
      Root = Math::Sqrt(k);
      Item = new ListViewItem(k.ToString());
      Item->SubItems->Add(Root.ToString(S"N", nfi));
      RootListView->Items->Add(Item);
      }
   }

It probably seems strange to see the creation of a CultureInfo object. The code above has the pointer MyCI point to this new object. You can use Help, Search in Visual Studio to look up information about the CultureInfo class. Although it is indeed used to work with language and other information that varies between cultures, it is also used to format numbers, which is why we use it here.

The next thing done in the above code is to set the nfi pointer so that it points at the NumberFormatInfo object inside of our CultureInfo object. The NumberFormat property is used to get this NumberFormatInfo object. Inside our NumberFormatInfo object we place 12 into the NumberDecimalDigits property. That is the key to getting the same number of decimal places displayed for all of our square roots. (Often we would use a lot fewer decimal place, but since we are using double precision reals, we have a lot of decimal places available. According to the help system in Visual Studio, up to 15 digits may be possible.) Finally, when we add the new root as a subitem, we convert it to a string while specifying nfi as the pointer to the formatting information to use. For more information on the use of formatting information with ToString, use the help system to look up double.ToString.

Try It Out