问题描述
我有一个gridview，其中有两个数据库表显示的信息。我想从业务名称列中选择业务名称，并根据用户选择viewfile的行从单元格中选择值，并将其分配给字符串变量。
这是我的代码（请注意，在点击'搜索内容'按钮后，page_load上没有显示gridview）
I have a gridview of which there is information displayed from two database tables. I want to select the business name from the "Business name" column and the value from the cell based on the row that the user selects 'viewfile' and assign it to a string variable.
Here is my code(note the gridview is not displayed on the page_load but after a 'search content' button is clicked)
protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
try
{
switch (e.CommandName)
{
case "view":
String name = GridView1.Rows[4].Cells[4].FindControl("Business_Name").ToString();
string filename = e.CommandArgument.ToString();
string path = Server.MapPath("~/BusinessProfilesContent/" + name + "/" + filename);
byte[] bts = System.IO.File.ReadAllBytes(path);
Response.Clear();
Response.ClearHeaders();
Response.ContentType = "image";
Response.WriteFile(path);
Response.Flush();
Response.End();
break;
}
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
}
这是webform代码：
Here is the webform code:
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="false"
EmptyDataText = "No files uploaded" Width="766px" onrowcommand="GridView1_RowCommand">
<Columns>
<asp:BoundField DataField = "Incident_ID" HeaderText = "Incident ID" />
<asp:BoundField DataField = "Incident_Type_Name" HeaderText = "Incident Type" />
<asp:BoundField DataField = "Description" HeaderText = "Description" />
<asp:BoundField DataField = "Date_Time" HeaderText = "Date and time of Upload" />
<asp:BoundField DataField = "Business_Name" HeaderText = "Business Name" />
<asp:BoundField DataField = "Provence" HeaderText = "Provence" />
<asp:BoundField DataField = "County" HeaderText = "County" />
<asp:BoundField DataField = "Username" HeaderText = "Username" />
<asp:ImageField DataImageUrlField="File_Path" ControlStyle-Width="100"
ControlStyle-Height = "100" HeaderText = "Preview Image"/>
<asp:TemplateField ItemStyle-HorizontalAlign = "Center">
<ItemTemplate>
<asp:LinkButton ID="LinkButton1" runat="server" CausesValidation="false" CommandName="view" CommandArgument = '<%#Eval("FileName")%>' >ViewFile</asp:LinkButton>
</ItemTemplate>
</asp:TemplateField>
</Columns>
</asp:GridView>推荐答案
对象引用未设置为对象的实例
object reference not set to an instance of an object
我认为是这行触发该异常
I think it is this line that is firing that exception
String name = GridView1.Rows[4].Cells[4].FindControl("Business_Name").ToString();
首先，我认为你不需要 .FindControl（商业名称） - 你没有一个名为的控件那 - 它是你的一个列的标题......实际上是列索引4.
其次，你总是在数据网格上查看行索引4 ...如果你还没有那里有5排？
这两个问题都可能产生错误。
现在解决它...
那个参数 GridViewCommandEventArgs e 派上用场找到被选中的行...
Firstly, I don't think you need the .FindControl("Business Name") - you don't have a control called that - it's the title of one of your columns... column index 4 in fact.
Secondly, you are always looking at row index 4 on your datagrid ... what if you haven't got 5 rows in there?
Both of these issues could have produced that error.
Now to solve it ...
That parameter GridViewCommandEventArgs e comes in handy for finding the row that was selected...
int i = Convert.ToInt32(e.CommandArgument);
GridViewRow r = GridView1.Rows[i];
接下来你想要的是与商业名称栏对应的单元格 - 我已经知道这是列索引4所以你的代码变成
Next you want the cell that corresponds to the "Business Name" column - I already know that this is column index 4 so your code becomes
String name = r.Cells[4].Text;
如果你不想硬编码列号（你不应该想看） []根据名称获取列
If you don't want to Hard-Code the column number (and you shouldn't want to) have a look at this post on StackOverflow[^] to get the column based on its name
protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
try
{
switch (e.CommandName)
{
case "view":
LinkButton l = e.CommandSource as LinkButton;
GridViewRow selectedRow = l.NamingContainer as GridViewRow ;
int intRowIndex = Convert.ToInt32(selectedRow.RowIndex);
GridViewRow row = GridView1.Rows[intRowIndex];
String name = Server.HtmlDecode(row.Cells[4].Text);
string filename = e.CommandArgument.ToString();
String ext = String.Empty;
string path = Server.MapPath("~/BusinessProfilesContent/" + name + "/" + filename);
SqlConnection conn;
SqlCommand comm;
String connectionString = ConfigurationManager.ConnectionStrings["ApplicationServices"].ConnectionString;
conn = new SqlConnection(connectionString);
comm = new SqlCommand("SELECT Incident.File_Extension FROM Incident JOIN User_Acc ON user_acc.User_id=incident.user_id JOIN business ON incident.business_id=business.Business_id JOIN incident_type ON incident_type.incident_type_id = incident.incident_type_id WHERE Business.Business_Name = Business.Business_Name AND Incident.FileName=@FileName", conn);
comm.Parameters.Add("@FileName", System.Data.SqlDbType.VarChar).Value = e.CommandArgument;
conn.Open();
SqlDataReader reader = comm.ExecuteReader();
while (reader.Read())
{
ext = reader["File_Extension"].ToString();
}
byte[] bts = System.IO.File.ReadAllBytes(path);
Response.Clear();
Response.ClearHeaders();
if (ext.Equals(".mov", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/quicktime";
}
else if (ext.Equals(".jpg", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "image/jpeg";
}
else if (ext.Equals(".jpeg", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "image/jpeg";
}
else if (ext.Equals(".gif", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "image/gif";
}
else if (ext.Equals(".mp2", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/mpeg";
}
else if (ext.Equals(".mpa", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/mpeg";
}
else if (ext.Equals(".mpe", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/mpeg";
}
else if (ext.Equals(".mpeg", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/mpeg";
}
else if (ext.Equals(".mpg", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/mpeg";
}
else if (ext.Equals(".mpv2", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/mpeg";
}
else if (ext.Equals(".qt", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/quicktime";
}
else if (ext.Equals(".avi", StringComparison.InvariantCultureIgnoreCase))
{
Response.ContentType = "video/x-msvideo";
}
Response.WriteFile(path);
Response.Flush();
Response.End();
break;
}
}
catch (Exception ex)
{
Response.Write(ex.Message);
}
}
这篇关于从gridview中的任何行，列或单元格中选择特定值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！