知道为什么一个赋值语句有效而另一个无效吗？

Question

这是我的代码：

string strSQL = "SELECT * from tMedia where SKU = '" + SKU + "'";
FbCommand command = new FbCommand(strSQL, databaseConn);

if (databaseConn.State == ConnectionState.Closed)
    databaseConn.Open();

FbDataReader data = command.ExecuteReader();
data.Read();  //  only one row is returned

//  assignment to "x" is empty (277?)
string x = (string)data["ProductType"].ToString();

//  find product type and set flag for later testing
//  obviously, these don't work either!
if (data["ProductType"].ToString().Contains("Video "))
    videoFormat = true;
else if (data["ProductType"].ToString().Contains("Music: "))
    audioFormat = true;

//  coProductType.Text assignment is correct
coProductType.Text = data["ProductType"].ToString();

Answer 1

也许您需要处理当有人输入无效的 SKU 并且没有返回任何数据行时会出现的问题。

Answer 2

由于唯一的区别是转换为字符串，因此合理的第一步似乎是删除它。无论如何应该没有必要。

Answer 3

它现在正在工作......如果有人感兴趣的话，这是代码......我不明白为什么将对象移动到方法之外使它起作用。如果有人能启发我，我将非常感激。

    string mediaFormat = "";
    bool video;
    bool audio;
    //---------------------------    populate the detail panel    ---------------------|
    private int PopulateDetailPanel(string SKU) {
        decimal convertedMoney;

        clearDetailPanel();  //  clear out old stuff

        //  now, find all data for this SKU
        if (databaseConn.State == ConnectionState.Closed)
            databaseConn.Open();

        string strSQL = "SELECT * from tMedia where SKU = '" + SKU + "'";
        FbCommand command = new FbCommand(strSQL, databaseConn);

        //  find product type and set flag for later testing
        FbDataReader data = command.ExecuteReader();
        data.Read();  //  only one row is returned

        coProductType.Text = data["ProductType"].ToString();  //  while we're here, might as well set it now
        mediaFormat = data["ProductType"].ToString();

        if (mediaFormat.Substring(0, 6) == "Video ")
            video = true;
        else if (mediaFormat.Substring(0, 7) == "Music: ")
            audio = true;