我在理解為什么我的一個組合框顯示過濾搜索而另一個沒有顯示時遇到問題，我對兩個組合框使用相同的代碼，但修改了一些鏈接到我的資料庫的 SQL 查詢。我還注意到，當我洗掉或注釋掉任何一個組合框的代碼時，過濾搜索發生在沒有被注釋或洗掉的那個組合框上。我還使用了“If, Else”陳述句，但仍然不起作用。我還希望使用兩個組合框來過濾 datagridview。請記住，一旦從組合框中選擇了專案，就會按下搜索按鈕以將資料過濾/顯示到資料網格視圖中。
親切的問候
這是我的代碼和表格：
[顯示冗余資料] https://i.stack.imgur.com/JEQI4.png
[ComboBox 品牌按預期作業] https://i.stack.imgur.com/6YyBf.png
[ComboBox 類別顯示所有內容，而不是顯示所選類別] https://i.stack.imgur.com/oEfII.png
Private Sub BtnSearch_Click(sender As Object, e As EventArgs) Handles BtnSearch.Click
If Not CmbBrand.SelectedIndex & CmbCategory.SelectedIndex = Nothing Then
BrandDisplay()
ElseIf CmbBrand.SelectedIndex & Not CmbCategory.SelectedIndex = Nothing Then
CategoryDisplay()
ElseIf Not CmbBrand.SelectedIndex & Not CmbCategory.SelectedIndex = Nothing Then
If DbConnect() Then
DgvRecord.Rows.Clear()
Dim SQLCmd As New OleDbCommand
With SQLCmd
.Connection = cn
.CommandText = "Select * " &
"From TblStock " &
"Where STCategory Like @CategorySearch"
.Parameters.AddWithValue("@CategorySearch", "%" & CmbCategory.Text & "%")
Dim rs As OleDbDataReader = .ExecuteReader()
SQLCmd.ExecuteReader()
While rs.Read
Dim NewStockRow As New DataGridViewRow()
NewStockRow.CreateCells(DgvRecord)
NewStockRow.SetValues({rs("StockID"), rs("STDateTime"), rs("STCategory"), rs("STBrand"), rs("STItemDescription"), rs("STSerialNumber"), rs("StockIn"), rs("StockOut"), rs("Stock")})
NewStockRow.Tag = rs("StockID")
DgvRecord.Rows.Add(NewStockRow)
End While
rs.Close()
If DgvRecord.Rows(0).Selected = True Then
MessageBox.Show("Please select a Category from the drop down list", "Category", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
End If
End With
End If
End If
cn.Close()
End Sub
Private Sub BrandDisplay()
If DbConnect() Then
DgvRecord.Rows.Clear()
Dim SQLCmd As New OleDbCommand
With SQLCmd
.Connection = cn
.CommandText = "Select * " &
"From TblStock " &
"Where STBrand Like @BrandSearch"
.Parameters.AddWithValue("@BrandSearch", "%" & CmbBrand.Text & "%")
Dim rs As OleDbDataReader = .ExecuteReader()
SQLCmd.ExecuteReader()
While rs.Read
Dim NewStockRow As New DataGridViewRow()
NewStockRow.CreateCells(DgvRecord)
NewStockRow.SetValues({rs("StockID"), rs("STDateTime"), rs("STCategory"), rs("STBrand"), rs("STItemDescription"), rs("STSerialNumber"), rs("StockIn"), rs("StockOut"), rs("Stock")})
NewStockRow.Tag = rs("StockID")
DgvRecord.Rows.Add(NewStockRow)
End While
rs.Close()
If DgvRecord.Rows(0).Selected = True Then
MessageBox.Show("Please select a Brand from the drop down list", "Brand", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
End If
End With
End If
cn.Close()
End Sub
Private Sub CategoryDisplay()
If DbConnect() Then
DgvRecord.Rows.Clear()
Dim SQLCmd As New OleDbCommand
With SQLCmd
.Connection = cn
.CommandText = "Select * " &
"From TblStock " &
"Where STCategory Like @CategorySearch"
.Parameters.AddWithValue("@CategorySearch", "%" & CmbCategory.Text & "%")
Dim rs As OleDbDataReader = .ExecuteReader()
SQLCmd.ExecuteReader()
While rs.Read
Dim NewStockRow As New DataGridViewRow()
NewStockRow.CreateCells(DgvRecord)
NewStockRow.SetValues({rs("StockID"), rs("STDateTime"), rs("STCategory"), rs("STBrand"), rs("STItemDescription"), rs("STSerialNumber"), rs("StockIn"), rs("StockOut"), rs("Stock")})
NewStockRow.Tag = rs("StockID")
DgvRecord.Rows.Add(NewStockRow)
End While
rs.Close()
If DgvRecord.Rows(0).Selected = True Then
MessageBox.Show("Please select a Category from the drop down list", "Category", MessageBoxButtons.OK, MessageBoxIcon.Exclamation)
End If
End With
End If
cn.Close()
End Sub
```
uj5u.com熱心網友回復：
將用戶界面代碼與資料庫代碼分開是個好主意。您的事件程序代碼應該相當簡短。
在使用它們的方法中宣告您的連接、命令和資料讀取器，以便可以處理它們。Using...End Using 塊為我們做這件事；他們也關閉了連接。將您的連接字串直接傳遞給連接的建構式。
對于每種可能性，我們都有不同的 CommandText 和 ParametersCollection。對于 Sql Server，使用 Add 方法而不是 AddWithValue。
Private Sub BtnSearch_Click(sender As Object, e As EventArgs) Handles BtnSearch.Click
Dim dt = GetSearchData(CmbBrand.Text, CmbCategory.Text)
DGVRecord.DataSource = dt
End Sub
Private Function GetSearchData(Brand As String, Category As String) As DataTable
Dim dt As New DataTable
Dim sqlString = "Select * From From TblStock "
Using cn As New SqlConnection("Your connection string"),
cmd As New SqlCommand()
cmd.Connection = cn
If Not String.IsNullOrEmpty(Brand) AndAlso Not String.IsNullOrEmpty(Category) Then
cmd.CommandText = sqlString & "Where STCategory = @CategorySearch And STBrand = @BrandSearch;"
cmd.Parameters.Add("@CategorySearch", SqlDbType.VarChar).Value = Brand
cmd.Parameters.Add("@BrandSearch", SqlDbType.VarChar).Value = Category
ElseIf Not String.IsNullOrEmpty(Brand) Then
cmd.CommandText = sqlString & "Where STBrand = @BrandSearch;"
cmd.Parameters.Add("@BrandSearch", SqlDbType.VarChar).Value = Category
ElseIf Not String.IsNullOrEmpty(Category) Then
cmd.CommandText = sqlString & "Where STCategory = @CategorySearch;"
cmd.Parameters.Add("@CategorySearch", SqlDbType.VarChar).Value = Brand
Else
cmd.CommandText = sqlString & ";"
End If
cn.Open()
Using reader = cmd.ExecuteReader()
dt.Load(reader)
End Using
End Using
Return dt
End Function
uj5u.com熱心網友回復：
為了更好地理解，您需要先更改那些“if... then... else...”。如果未選擇組合框，它將具有值 -1，因此您可以這樣做：
Dim bBrandIsSelected as boolean = CmbBrand.SelectedIndex <> -1
Dim bCategoryIsSelected as boolean = CmbCategory.SelectedIndex <> -1
現在您可以更輕松地構建代碼，例如：
If bBrandIsSelected AndAlso bCategoryIsSelected then
' do something
else
if bBrandIsSelected then
BrandDisplay()
else
if bCategoryIsSelected then
CategoryDisplay()
End if
End if
End if
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