嘗試添加並顯示ListBox中的值的總和...獲取錯誤：System.InvalidCastException：'指定的轉換無效。'

Question

我想獲得列表框中所有值的總和，我想在文本框中顯示結果。當我運行該程序並單擊該按鈕時，出現以下錯誤：System.InvalidCastException：'指定的轉換無效。'

private void readButton_Click(object sender, EventArgs e) 
    { 
     int counter = 0; 
     string line; 
     System.IO.StreamReader file = new System.IO.StreamReader(@"C:\Users\Harra\Documents\Visual Studio 2017\Projects\File Reader\Sales.txt"); 
     while ((line = file.ReadLine()) != null) 
     { 
      displayListBox.Items.Add(line); 
      counter++; 
     } 
     { 

      int intTotal = 0; 
      int intCounter; 
      double dblAdd; 

      for (intCounter = 0; intCounter <= displayListBox.Items.Count - 1; intCounter++) 

      { 
       intTotal += Convert.ToInt32(displayListBox.Items[intCounter]; 
      } 

      dblAdd = (double)intTotal; 

      //trying to display total to textbox 
      totalTextBox.Text = string.Format("{0:F}", dblAdd); 
     } 

    } 

Answer 1

您的意見和更多的細節之後，我覺得這應該工作：

private void readButton_Click(object sender, EventArgs e) 
{ 
    string line; 
    System.IO.StreamReader file = new System.IO.StreamReader(@"C:\Users\Harra\Documents\Visual Studio 2017\Projects\File Reader\Sales.txt"); 
    double dblAdd = 0; 
    while ((line = file.ReadLine()) != null) 
    { 
     displayListBox.Items.Add(line); 
     dblAdd += Convert.ToDouble(line); 
    } 
    totalTextBox.Text = string.Format("{0:F}", dblAdd); 
}