通過值C＃從數組中多選ListBox項

Question

我想從數組中多選項目，

出於某種原因，此代碼將引發NullReferenceException異常：

        int[] players = Playerss.GetAllPlayersIDbyMovieID(movie);
        foreach (int playerID in players)
        {
            PlayersListBox.Items.FindByValue(playerID.ToString()).Selected = true;
        }

當我改用此代碼時，它可以工作，但只會保留最后選擇的選項：

            int[] players = Playerss.GetAllPlayersIDbyMovieID(movie);
            foreach (int playerID in players)
            {
                PlayersListBox.SelectedValue += playerID.ToString();
            }

ASP .NET文件：

<asp:ListBox ID="PlayersListBox" runat="server" 
            SelectionMode="Multiple"
                   DataSourceID="PlayersAccessDataSource"
                      DataTextField="Player" 
                      DataValueField="PlayerID"           

            ></asp:ListBox> 

Answer 1

Playerss.GetAllPlayersIDbyMovieID(movie); 

您可能會收到一個空異常請求，因為在Playerss.GetAllPlayersIDbyMovieID（movie）方法的結果中某處有一個選項在PlayersListBox.Items中不可用

在嘗試為不存在的對象設置屬性值之前，可以通過檢查null來解決此問題。

int[] players = Playerss.GetAllPlayersIDbyMovieID(movie);
    foreach (int playerID in players)
    {
        var player = PlayersListBox.Items.FindByValue(playerID.ToString());
        if (player != null) 
        {
            player.Selected = true;
        }
    }