ASP.NET C#,需要按两次按钮才能发生一些事情

我有一个Web应用程序,问题是标签中的文本在第一次单击时不会更新,我需要单击按钮两次,我调试代码,然后我发现标签没有重新获取数据直到之后第二次点击,

这是我的代码：

System.Data.sqlClient.sqlCommand command = new System.Data.sqlClient.sqlCommand();
System.Data.sqlClient.sqlConnection connection;
string CommandText;
string game;
string modtype;
bool filter;
protected void Page_Load(object sender,EventArgs e)
{

    labDownloadList.Text = null;

    //Session variables:
    if (Session["Game"] != null)
    {
        game = Convert.ToString(Session["Game"]);
    }
    if (Session["ModType"] != null)
    {
        modtype = Convert.ToString(Session["ModType"]);
    }
    if (Session["FilterBool"] != null)
    {
        filter = Convert.ToBoolean(Session["FilterBool"]);
    }
    string ConnectionString = "Data Source=.\\sqlEXPRESS;AttachDbFilename=C:\\inetpub\\wwwroot\\stian\\App_Data\\Database.mdf;Integrated Security=True;User Instance=True";
    connection = new System.Data.sqlClient.sqlConnection(ConnectionString);
    System.Data.sqlClient.sqlDataReader reader;
    command = connection.CreateCommand();
    connection.open();
    CommandText = "SELECT * FROM Command";
    if (filter)
    {
        CommandText = "SELECT * FROM Command WHERE Game='" + game + "' AND Type='" + modtype + "'";
    }
    command.CommandText = CommandText;
    reader = command.ExecuteReader();
    labDownloadList.Text = "";
    while (reader.Read())
    {
        string game = reader.GetString(1);
        string author = reader.GetString(2);
        string downloadlink = reader.GetString(3);
        string size = reader.GetString(4);
        string description = reader.GetString(5);
        string version = reader.GetString(6);
        string screenshotlink = reader.GetString(7);
        Int64 AmountDownloaded = reader.GetInt64(8);

        labDownloadList.Text += "Game: " + game + "<br>";
        labDownloadList.Text += "Author: " + author + "<br>";
        labDownloadList.Text += "Size: " + size + "<br>";
        labDownloadList.Text += "Description: " + description + "<br>";
        labDownloadList.Text += "Version: " + version + "<br>";
        labDownloadList.Text += "<img src='" + screenshotlink + " /><br>";
        labDownloadList.Text += "Downloaded: " + AmountDownloaded + " times<br><hr>";
        labDownloadList.Text += "<a href='" + downloadlink + "'>Download</a><br>";
    }
}

protected void Page_UnLoad(object sender,EventArgs e)
{
    Session["Game"] = game;
    Session["ModType"] = modtype;
    Session["FilterBool"] = filter;
    connection.Close();
}

protected void btnFilter_Click(object sender,EventArgs e)
{
    game = lstGames.SelectedValue;
    modtype = lstTypeMod.SelectedValue;
    filter = true;
}

解决方法

要非常清楚.按钮单击事件发生在Page_Load事件之后,意味着未在第一个回发上应用过滤.它已在第二次回发时更新,您会看到过滤.让代码工作的最简单的变化是将Page_Load事件中的所有代码移动到OnPreRender中,以便在按钮单击事件之后重新加载.

然而,一个更干净的解决方案可能是将它移动到LoadData函数中,并在它不是回发时在PageLoad上调用它,并在更新过滤器后在按钮单击事件上调用它.这将阻止在不需要重新加载数据的任何回发页面循环上调用数据库：

  protected void Page_Load(object sender,EventArgs e)
{    
    if (!Page.IsPostBack)
        {   
             LoadData()
        }
}

private void LoadData()
{
    labDownloadList.Text = null;
    //Session variables:    
    if (Session["Game"] != null)
    ...
}

protected void btnFilter_Click(object sender,EventArgs e)
{    
    game = lstGames.SelectedValue;
    modtype = lstTypeMod.SelectedValue;
    filter = true;
    LoadData();
}

对于初露头角的ASP.Net开发人员来说,最后一条快速建议是彻底了解页面生命周期.了解页面上的事件顺序至关重要.祝好运.

原文地址：https://www.jb51.cc/aspnet/248148.html