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Search Functionality using LINQ
The file, “Countries.txt” contains a list of countries from around the world. Place this file in your bin/debug directory.
In this assignment, you will create a Visual Basic program that reads the values from the Countries text file, displays those countries in a listbox, and allows the user to enter characters in a textbox to search for one or more countries in the listbox and display the results in another listbox. The number of countries returned from the search is displayed in a textbox below the results. The program also allows the user to sort the countries listbox in ascending or descending order. Finally, a clear button clears the results in the listbox, the search textbox, and the number of countries returned from the search textbox. A quit button is provided, which exits the application.
The figures below show the output of the Visual Basic program that performs the functionality described above.
1. Write a Visual Basic program that displays the information below and performs the functionality described above.
2. Using the IO.File.ReadAllLines method, read the contents of the countries.txt file into an array.
3. When the form loads, display the contents of the array in the Coutnries listbox.
4. When the user enters something in the Search Country textbox and presses the “Go” button, the program should search the array upon which the countries listbox is displayed. Use a LINQ query to do this. Note that the user may type in a full country name as illustrated in Figure 1 below, or he may enter only part of the name (even one letter), and the listbox should be populated with all countries that start with the same letter(s) as those entered by the user. Figure 2 below illustrates the search for all countries that begin with the letter “D”.
a. Be sure to make your search NON-case sensitive. That is, if the user enters “UnItEd sTateS” in the textbox, it should still retrieve the country “United States”. [Hint: If you convert the value that the user enters into uppercase and search for values that are converted to uppercase, this allows for a match to be found.]
b. Using LINQ queries, write the code such that when the user clicks the Sort Ascending button, the countries displayed in the Countries listbox is sorted from A-Z. Conversely, when the user clicks the Sort Descending button, the listbox should be sorted from Z-A. Although this feature can be accomplished using the properties of the listbox, your code should be written using LINQ queries to perform these functions.
[Hint: Before you set the datasource property of your listbox to the results of your LINQ query, you must first remove the datasource linkage to the original array by setting .datasource = nothing.]
5. Using a certain property of listboxes, determine the number of search results displayed in the Results listbox and display that number in the textbox shown below the listbox. Note: Do NOT use a LINQ query for this task.
6. Use appropriate software development guidelines, such as clearing the results listbox before populating it with new data when the Go button is clicked and including a title on the form.
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