c# - 变量恢复到初始值

Question

下面我去掉了不相关的代码。我创建了一个名为 printString 的字段。 calculateButton_Click 方法执行大量操作，然后我想使用 response.write 将其发送到适合打印的页面。然而，printString 变量似乎并没有停止成为“DEFAULT”。当我单击 printButton_Click 时，DEFAULT 是我空白页上显示的所有内容。修剪代码如下:

    public partial class _Default : System.Web.UI.Page
    {
        private string _printString = "DEFAULT";

        protected void Page_Load(object sender, EventArgs e)
        {
            Response.Buffer = true;
        }

        protected void calculateButton_Click(object sender, EventArgs e)
        {
            _printString = "";

_printString = "HARRY POTTER™: THE EXHIBITION Invoice<BR>Today's date: " + DateTime.Today.ToString("dd/MM/yyyy") + "<BR>Visit date: " +
            dateSelectedString + "<BR><BR><BR>Adult tickets: " + numAdult + "<BR>Child tickets: " + numChild + "<BR>Family Passes: " + numFamily +
            "<BR>Payment method: " + paymentType + "<BR>Total to pay: $" + totalPrice.ToString("0.00");

    }

    protected void printButton_Click(object sender, EventArgs e)
    {
        Response.Clear();
        Response.Write(_printString);
        Response.Flush();
        Response.End();
    }
}

Answer 1

单击 printButton 时，它使用设置变量时的值 DEFAULT。

private string _printString = "DEFAULT";

是你的问题。当变量被修改时，您需要维护 printString 的状态。简单地将 _printString 分配给另一个值并不能持久化更改。您可以编写一个函数，在单击 printButton 时将 _printString 分配给正确的值，使用 ViewState 或 Session或者直接在 printButton 点击函数中赋值 _printString 如下所示。

protected void printButton_Click(object sender, EventArgs e)
{
    _printString = "Harry Potter";

    Response.Clear();
    Response.Write(_printString);
    Response.Flush();
    Response.End();
}

将导致 Harry Potter 被写入页面。

要使用Session:

protected void calculateButton_Click(object sender, EventArgs e)
{
       _printString = "HARRY POTTER™: THE EXHIBITION Invoice<BR>Today's date: " + DateTime.Today.ToString("dd/MM/yyyy") + "<BR>Visit date: " +
        dateSelectedString + "<BR><BR><BR>Adult tickets: " + numAdult + "<BR>Child tickets: " + numChild + "<BR>Family Passes: " + numFamily +
        "<BR>Payment method: " + paymentType + "<BR>Total to pay: $" + totalPrice.ToString("0.00");

       Session["PrintString"] = _printString;
}

protected void printButton_Click(object sender, EventArgs e)
{
    _printString = (string)Session["PrintString"];

    Response.Clear();
    Response.Write(_printString);
    Response.Flush();
    Response.End();
}

View 状态:

ViewState["PrintString"] = "HarryPotter";

然后要检索您可以简单地执行的值:

 _printString = (string)ViewState["PrintString"];

http://msdn.microsoft.com/en-gb/library/ms972976.aspx