Visual Studio C＃通用哈希表字典如果if语句错误？

Question

I am creating a GUI in Visual Studio where a Dictionary collection will be created. This will contain instances of book classes which will contain the string members Title, ISBN and a Boolean variable called Onloan. these members will be entered by the user and submitted into the dictionary. The user can also search books they have entered and change their loan status.

I want the program to be able to search for books even if the user only enters the ISBN or the Title, currently it only works when both a Title and ISBN are searched for together. if the user only searches for an ISBN, the Title in the search results text box is blank and if the user only searches the Title the ISBN search results text box states "temp" which is the temporary value I used in a temporary book I used to search.

I've have been changing the program for some time trying to figure out why this happens. I'm wondering if someone can explain it. Maybe I have written the if statements incorrectly.

Book Class

class Books
    {
        private String isbn;
        private string title;
        private Boolean onloan;

        public Books(string isbn, string title)
        {
            this.isbn = isbn;
            onloan = false;
        }
        public string ISBN
        {
            get { return this.isbn; }
            set { this.isbn = value; }
        }
        public string Title
        {
            get { return this.title; }
            set { this.title = value; }
        }
        public Boolean Onloan
        {
            get { return this.onloan; }
            set { this.onloan = value; }
        }
    }

Form:

public partial class Form1 : Form

     {


       Dictionary<string, Books> Library = new Dictionary<string, Books>();

        public Form1()
        {
            InitializeComponent();
        }

        private void button1_Click(object sender, EventArgs e)   //submit button
        {
            if ((String.IsNullOrWhiteSpace(TitleBox.Text) == false && String.IsNullOrWhiteSpace(ISBNBox.Text) == false) || 
                (String.IsNullOrEmpty(TitleBox.Text) == false && String.IsNullOrEmpty(ISBNBox.Text) == false))
            {
                Books LibBook = new Books(ISBNBox.Text, TitleBox.Text);
                if(LoanRadial.Checked == true)
                    {
                    LibBook.Onloan = true;
                    LoanRadial.Checked = false;
                    }

                Library.Add(ISBNBox.Text, LibBook);
                TitleBox.Clear();
                ISBNBox.Clear();
                //int count = Library.Count();
                //ISBNBox.Text = count.ToString();

            }
        }

        private void Remove_Click(object sender, EventArgs e)
        {
            Library.Remove(ISBNBox.Text);
            TitleBox.Clear();
            ISBNBox.Clear();
            if (LoanRadial.Checked == true)
            {
                LoanRadial.Checked = false;
            }
        }

        private void Search_Click(object sender, EventArgs e)
        {
            string tempstring = "temp";
            Books tempbook = new Books(tempstring, tempstring);
            if ((String.IsNullOrWhiteSpace(ISBNBox.Text) == false && String.IsNullOrWhiteSpace(TitleBox.Text) == true) ||
                (String.IsNullOrEmpty(ISBNBox.Text) == false && String.IsNullOrEmpty(TitleBox.Text) == true))
            {

                tempbook.ISBN = ISBNBox.Text;
                foreach (KeyValuePair<string, Books> element in Library)
                {
                    if (tempbook.ISBN == element.Value.ISBN)
                    {
                        tempbook.Title = element.Value.Title;
                        tempbook.Onloan = element.Value.Onloan;
                    }
                }
                Titlebox2.Text = tempbook.Title;
                ISBN2.Text = tempbook.ISBN;
                if (tempbook.Onloan == true)
                {
                    LoanBox.Text = tempbook.Title + " Is on loan";
                }
                else
                {
                    LoanBox.Text = tempbook.Title + " Is not on loan";
                }

            }
            else if ((String.IsNullOrWhiteSpace(ISBNBox.Text) == true && String.IsNullOrWhiteSpace(TitleBox.Text) == false) ||
                (String.IsNullOrEmpty(ISBNBox.Text) == true && String.IsNullOrEmpty(TitleBox.Text) == false))
            {
                tempbook.Title = TitleBox.Text;
                foreach (KeyValuePair<string, Books> element in Library)
                {
                    if (tempbook.Title == element.Value.Title)
                    {

                        tempbook.ISBN = element.Value.ISBN;
                        tempbook.Onloan = element.Value.Onloan;
                    }
                }
                Titlebox2.Text = tempbook.Title;
                ISBN2.Text = tempbook.ISBN;
                if (tempbook.Onloan == true)
                {
                    LoanBox.Text = tempbook.Title + " Is on loan";
                }
                else
                {
                    LoanBox.Text = tempbook.Title + " Is not on loan";
                }
            }
            else if ((String.IsNullOrWhiteSpace(ISBNBox.Text) == false && String.IsNullOrWhiteSpace(TitleBox.Text) == false) ||
                    (String.IsNullOrEmpty(ISBNBox.Text) == false && String.IsNullOrEmpty(TitleBox.Text) == false))
            {

                tempbook.ISBN = ISBNBox.Text;
                tempbook.Title = TitleBox.Text;
                foreach (KeyValuePair<string, Books> element in Library)
                {
                    if ((tempbook.Title == element.Value.Title) &&  (tempbook.ISBN == element.Value.ISBN) )
                    {
                        tempbook.Onloan = element.Value.Onloan;
                    }                   
                }
                Titlebox2.Text = tempbook.Title;
                ISBN2.Text = tempbook.ISBN;
                if (tempbook.Onloan == true)
                {
                    LoanBox.Text = tempbook.Title + " Is on loan";
                }
                else
                {
                    LoanBox.Text = tempbook.Title + " Is not on loan";
                }

            }
        }

        private void Changeloan_Click(object sender, EventArgs e)
        {
            string tempstring = "temp";
            Books tempbook = new Books(tempstring, tempstring);
            if ((String.IsNullOrWhiteSpace(ISBN2.Text) == false && String.IsNullOrWhiteSpace(Titlebox2.Text) == false) ||
                (String.IsNullOrEmpty(ISBN2.Text) == false && String.IsNullOrEmpty(Titlebox2.Text) == false))
            {
                tempbook.ISBN = ISBN2.Text;
                tempbook.Title = Titlebox2.Text;
                foreach (KeyValuePair<string, Books> element in Library)
                {
                    if ((tempbook.ISBN == element.Value.ISBN) && (tempbook.Title == element.Value.Title))
                    {

                        if (element.Value.Onloan == true)
                        {
                            element.Value.Onloan = false;
                            LoanBox.Text = tempbook.Title + " Is not on loan";
                        }
                        else
                        {
                            element.Value.Onloan = true;
                            LoanBox.Text = tempbook.Title + " Is not on loan";
                        }
                    }
                }
            }                  
            else if ((String.IsNullOrWhiteSpace(ISBN2.Text) == true && String.IsNullOrWhiteSpace(Titlebox2.Text) == false) ||
                (String.IsNullOrEmpty(ISBN2.Text) == true) && (String.IsNullOrEmpty(Titlebox2.Text) == false))
            {
                tempbook.Title = Titlebox2.Text;
                foreach (KeyValuePair<string, Books> element in Library)
                {
                    if(tempbook.Title == element.Value.Title)
                    {
                        if (element.Value.Onloan == true)
                        {
                            element.Value.Onloan = false;
                            LoanBox.Text = element.Value.Title + " Is not on loan";

                        }
                        else if (element.Value.Onloan == false)
                        {
                            element.Value.Onloan = true;
                            LoanBox.Text = element.Value.Title + " Is on loan";
                        }
                    }
                }

                    }
            else if((String.IsNullOrWhiteSpace(ISBN2.Text) == false) && (String.IsNullOrWhiteSpace(Titlebox2.Text) == true) || 
                (String.IsNullOrEmpty(ISBN2.Text) == false) && (String.IsNullOrEmpty(Titlebox2.Text) == true))
            {
                tempbook.ISBN = ISBN2.Text;
                foreach (KeyValuePair<string, Books> element in Library)
                {
                    if (tempbook.ISBN == element.Value.ISBN)
                    {
                        if (element.Value.Onloan == true)
                        {
                            element.Value.Onloan = false;
                            LoanBox.Text = element.Value.Title + " Is not on loan";

                        }
                        else if (element.Value.Onloan == false)
                        {
                            element.Value.Onloan = true;
                            LoanBox.Text = element.Value.Title + " Is on loan";
                        }
                    }
                }
            }

            }
        }

Books form picture

Answer 1

You are using a Dictionary , but more as a list of tuples than a proper hash table. I'm assuming your key is the ISBN, in which case you might get the book from the dictionary like this:

String isbn = ISBNBox.Text; //Assuming the TextBox.Text is valid
if(Library.ContainsKey(isbn))
{
    Books book = Library[isbn];
    //Do whatever you want to do with the book
}

Addressing the other aspect of your problem, where the text is being set to the tempbook ISBN "temp", any time the title or ISBN entered are not found in the Library, they will be set to the temp values. This is because you are setting the textbook values

Titlebox2.Text = tempbook.Title;
ISBN2.Text = tempbook.ISBN;

even if the book is not found in the dictionary. Consider having some case for when the book is not found.

If the ISBN is indeed your key, then if they provide one then don't need to worry about the title. You really only need to iterate through the dictionary if they only give you the title. Also, you can do your setting of the UI properties at the end to reduce some of the redundant code. Here's a bit of a refactor with a place for code to handle when a book isn't found:

private void Search_Click(object sender, EventArgs e)
{
    Books tempbook = null;
    if (String.IsNullOrWhiteSpace(ISBNBox.Text) == false && String.IsNullOrEmpty(ISBNBox.Text) == false)
    {
        String isbn = ISBNBox.Text;
        if(Library.ContainsKey(isbn)){
            tempbook = Library[isbn];
        }

    }
    else if (String.IsNullOrWhiteSpace(TitleBox.Text) == false && String.IsNullOrEmpty(TitleBox.Text) == false)
    {
        String title = TitleBox.Text;
        foreach (KeyValuePair<string, Books> element in Library)
        {
            if (element.Value.Title == title)
            {

                tempbook = element.Value;
                break;
            }
        }
    }    
    if(tempbook != null)
        Titlebox2.Text = tempbook.Title;
        ISBN2.Text = tempbook.ISBN;
        if (tempbook.Onloan == true)
        {
            LoanBox.Text = tempbook.Title + " Is on loan";
        }
        else
        {
            LoanBox.Text = tempbook.Title + " Is not on loan";
        }

    } else {
    //Handle case where book is not found
    }
}

Also, your class describing a book is called Books , but since a single object of the class would be just one book, it would probably be better named simply Book .