使用C＃和JSON在ASP.Net中填充下拉列表和文本框

Question

This is my first question on Stack overflow so thank you in advance for any help/ advice given.

I am currently making a "Library Database" using only ASP.Net and C#. It is a university assignment and we are limited to this, Data must be saved and withdrawn using JSON.

While i have been able to Add a book listing and display the listing in a grid view, I need to be able to display and edit the information using a standard form, using a drop down list and text boxes to display each section. The below code snippet shows the Book class used to keep all the variables for the JSON File

 public class Book
{
    public string id { get; set; }
    public string title { get; set; }
    public string author { get; set; }
    public string year { get; set; }
    public string publisher { get; set; }
    public string isbn { get; set; }

    public Book(string id, string title, string author, string year, string publisher, string isbn)
    {
        this.id = id;
        this.title = title;
        this.author = author;
        this.year = year;
        this.publisher = publisher;
        this.isbn = isbn;       
    }
}

The below code shows the Other class being used to generate a list from the above variables.

public class BookList
{
    public List<Book> bookList { get; set; }

    public BookList()
    {
        bookList = new List<Book>();
    }
}

The below code shows what i currently have for my Edit Book Page.

public partial class EditBook : System.Web.UI.Page
{
    public const string FILENAME = @"C:\Users\User\Documents\Assessments\19383038_CSE2ICX_Assignment3\JsonFiles\BookList.Json";
    string jsonText = " ";
    BookList bookList = new BookList();  

    protected void Page_Load(object sender, EventArgs e)
    {
        try
        {
            jsonText = File.ReadAllText(FILENAME);
        }
        catch (FileNotFoundException)
        {

        }
        BookList bookList = JsonConvert.DeserializeObject<BookList>(jsonText);
        JObject jObj = JObject.Parse(jsonText);
        if (!IsPostBack)
        {

            ddl.DataTextField = "id";
            ddl.DataValueField = "id";
            ddl.DataSource = bookList.bookList;
            ddl.DataBind();
        }

    }

    protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
    {

        txtEnterID.Text = "";
    }

Now, I have managed to populate the Drop Down List, but hours of research and racking my brain, i cannot find a way to translate that onto the text boxes. Currently I have no way of having the Textboxes a) Identify which value the Drop down list is using b) Using that value to determine which variable of the JSON file it uses, and from which group.

Now im aware that its very likely I cannot use this method to populate the text boxes, and probably need to start from scratch. I don't need the code handed to me, but i would appreciate if someone could give me an example snippet, or push me on to the write track with how to tackle this task.

Please no Ajax, Jquery or java.

Thank you again if you made it to the end.

Answer 1

I haven't had time to test this code. But the ideia is pretty simple. You get the sender variable and convert it to DropDownList class and use its SelectedItem property.

  protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
    {
        var selectedValue = (Book)((DropDownList)sender).SelectedItem.Value;
        txtEnterID.Text = selectedValue.title;
    }

Hope it helps :)

Answer 2

I think you are looking for something like this inside the SelectedIndexChanged method:

//get your list of books
BookList bookList = JsonConvert.DeserializeObject<BookList>(jsonText);

//select the correct book from the list using Linq and the selected value from ddl
var book = bookList.bookList.Where(x => x.id == ddl.SelectedValue).FirstOrDefault();

//show the book properties in the textboxes
txtEnterID.Text = book.id;
txtTitle.Text = book.title;

Answer 3

I'm not sure if this works, but this usually works for me, so I hope it helps you too.

 protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
    {

        txtEnterID.Text = ddl.SelectedItem.Value.ToString();

    }

Also, could I ask why you load the dropdownlist data text field as id and not book name?