計算結果，如果組合框的值已更改

我有一個計算，其中我將面板數乘以瓦特數，並將輸出轉換爲KW。這是我的VB代碼。計算結果，如果組合框的值已更改

Total_watt = (Watt_In * Npanel)/1000.0

如果我更改DomainUpDown，將會生成結果。如果我選擇一個ComboBox項目，值不會改變。我已經添加了幾行來處理組合框，但我正在逐漸

「」類型的異常出現在Microsoft.VisualBasic.dll中，但在用戶代碼中其他信息沒有處理錯誤：轉換從字符串「」到類型「整數」無效。

沒有ComboBox代碼，它工作正常，但無法從ComboBox中獲取數據。

Public Class Solar_Panel 
    Dim Total_watt As Double 
    Dim Npanel As Integer 
    Dim Watt_In As Integer 
    Private Sub Solar_Panel_Load(sender As Object, e As EventArgs) Handles MyBase.Load 
     RadioButton_Direct_Data_In.Select() 
     Watt_In = CInt(ComboBox_PanelWatt.SelectedItem) 
     Npanel = CInt(DomainUpDown_NModule.Text) 
     Total_watt = (Watt_In * Npanel)/1000.0 
     Label_Tout.Text = CStr(Total_watt) 
    End Sub 

    Private Sub DomainUpDown_NModule_SelectedItemChanged(sender As Object, e As EventArgs) Handles DomainUpDown_NModule.SelectedItemChanged 
     Watt_In = CInt(ComboBox_PanelWatt.SelectedItem) 
     Npanel = CInt(DomainUpDown_NModule.Text) 
     Total_watt = (Watt_In * Npanel)/1000.0 
     Label_Tout.Text = CStr(Total_watt) 
    End Sub 

    Private Sub ComboBox_PanelWatt_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox_PanelWatt.SelectedIndexChanged 
     If ComboBox_PanelWatt.Text = True Then 
      Watt_In = CInt(ComboBox_PanelWatt.SelectedItem) 
      Npanel = CInt(DomainUpDown_NModule.Text) 
      Total_watt = (Watt_In * Npanel)/1000.0 
      Label_Tout.Text = CStr(Total_watt) 
     End If 
    End Sub 
End Class

來源

2015-09-14 Ajith Nayak

你的錯誤可能是試圖在沒有ComboBox項已被選中的文本轉換在ComboBox成整數的結果（等Text屬性是一個空字符串）。

我有幾個建議，我認爲會改善你的類：

，你要正確對待它的值爲數字使用NumericUpDown控件，而不是一個DomainUpDown。
將計算總瓦數的代碼移動到Sub，以便您只需編寫一次代碼即可。
如果ComboBox文本爲空，則跳過計算。
使用Integer.TryParse驗證ComboBox文本並將其轉換爲整數。

如果您允許用戶在ComboBox中鍵入自己的值，則需要處理ComboBox的TextChanged事件而不是SelectedIndexChanged事件。

Public Class Solar_Panel 
    Private TotalKWatts As Double 
    Private Watt_In, NPanel As Integer 

    Private Sub Solar_Panel_Load(sender As Object, e As EventArgs) Handles MyBase.Load 
     'The NumericUpDown properties could be set in the designer instead of here 
     NumericUpDown_NModule.Minimum = 0 
     NumericUpDown_NModule.Maximum = 100 
     NumericUpDown_NModule.DecimalPlaces = 0 
     NumericUpDown_NModule.Increment = 1 

     RadioButton_Direct_Data_In.Select() 
     GetTotalWatts 
    End Sub 

    Sub NumericUpDown_NModule_ValueChanged(sender As Object, e As EventArgs) Handles NumericUpDown_NModule.ValueChanged 
     GetTotalWatts 
    End Sub 

    Sub ComboBox_PanelWatt_SelectedIndexChanged(sender As Object, e As EventArgs) Handles ComboBox_PanelWatt.SelectedIndexChanged 
     GetTotalWatts 
    End Sub 

    Private Sub GetTotalWatts()  
     If ComboBox_PanelWatt.Text = "" Then Exit Sub 
     If Integer.TryParse(ComboBox_PanelWatt.Text, Watt_In) Then 
      NPanel = CInt(NumericUpDown_NModule.Value) 
      TotalKWatts = NPanel * Watt_In/1000 
      Label_Tout.Text = TotalKWatts.ToString() 
     Else 
      Label_Tout.Text = "Invalid wattage" 
     End If 
    End Sub 
End Class

來源

2015-09-14 13:15:58 Blackwood

計算結果，如果組合框的值已更改

回答

相關問題