如果輸入數據庫中不存在的輸入，如何輸出錯誤消息？ N-

Question

關於我的問題的快速簡要說明：如果我輸入的程序的數據庫中不存在的數字，我希望我的程序能夠在不使程序崩潰的情況下打印出錯誤消息。這裏是我的代碼：

listBox1.Items.Clear(); 

    BusinessTier.Business BT = new BusinessTier.Business("netflix.mdf"); 

    if (this.txtMovieID == null) //Hoping this would work and return to the program if I enter a wrong input. 
    { 
    listBox1.Items.Add("**Error, this movie ID doesn't exist, or database is empty?!"); 
    } 

    int N = System.Convert.ToInt32(this.txtMovieID.Text); 
    BusinessTier.Movie movie = BT.GetMovie(N); 

    BusinessTier.MovieDetail movieid = BT.GetMovieDetail(movie.MovieID); //this part will crash the program if I type a number like 0 or greater than 250 when my database contained 250 rows. 


    //display results: 

    listBox1.Items.Add(movie.MovieName); 

    foreach (BusinessTier.Review r in movieid.Reviews) 
    { 
    listBox1.Items.Add(r.UserID + ": " + r.Rating); 
    } 

Answer 1

第一件事：你仍在處理過程中的剩餘部分，即檢索電影細節，即使this.txtMovieID爲null。你需要停止加工和return

listBox1.Items.Clear(); 

    BusinessTier.Business BT = new BusinessTier.Business("netflix.mdf"); 

    if (this.txtMovieID == null) //Hoping this would work and return to the program if I enter a wrong input. 
    { 
    listBox1.Items.Add("**Error, this movie ID doesn't exist, or database is empty?!"); 
    return; // exit out if the MovieID is null 
    } 

二：把支票看到GetMovie(N)結果是否爲空或不是，如果是空，突破和return

int N = System.Convert.ToInt32(this.txtMovieID.Text); 
    BusinessTier.Movie movie = BT.GetMovie(N); 

    if (movie == null) return; // exit if the GetMovie result is null 

    BusinessTier.MovieDetail movieid = BT.GetMovieDetail(movie.MovieID); //this part will crash the program if I type a number like 0 or greater than 250 when my database contained 250 rows. 

    //display results: 

    listBox1.Items.Add(movie.MovieName); 

    foreach (BusinessTier.Review r in movieid.Reviews) 
    { 
     listBox1.Items.Add(r.UserID + ": " + r.Rating); 
    }