Question

当我选择项目时，网格工作正常但是......当我按下左键选择其他练习时，应用程序崩溃。

这是代码：

int specialbtnId = 0;

private void gvSpecialPagesViewExercise_SelectionChanged(object sender,
    SelectionChangedEventArgs e)
{
    switch (specialbtnId)
    {
        case 0:
            LoadSpecialPagesBookExcersices(lstCurrentPageLeftButton1Excersices
                .ElementAt(gvSpecialPagesViewExercise.SelectedIndex));
            break;
        case 1:
            LoadSpecialPagesBookExcersices(lstCurrentPageLeftButton2Excersices
                .ElementAt(gvSpecialPagesViewExercise.SelectedIndex));
            break;
        case 2:
            LoadSpecialPagesBookExcersices(lstCurrentPageLeftButton3Excersices
                .ElementAt(gvSpecialPagesViewExercise.SelectedIndex));
            break;
        case 3:
            LoadSpecialPagesBookExcersices(lstCurrentPageLeftButton4Excersices
                .ElementAt(gvSpecialPagesViewExercise.SelectedIndex));
            break;
    }
}

这是另一个发泄按钮，是我现在用来改变练习和部分练习的唯一代码。

private void UpdateLeftButtonContent()
    {
        ResetSpecialPagesButtonColors();
        if (currentPageSettings.PageStyle.Contains("Especiales"))
        {
            if (lstCurrentPageLeftButton1Excersices != null)
                lstCurrentPageLeftButton1Excersices.Clear();
            if (lstCurrentPageLeftButton2Excersices != null)
                lstCurrentPageLeftButton2Excersices.Clear();
            if (lstCurrentPageLeftButton3Excersices != null)
                lstCurrentPageLeftButton3Excersices.Clear();
            if (lstCurrentPageLeftButton4Excersices != null)
                lstCurrentPageLeftButton4Excersices.Clear();
            foreach (BookExercises x in lstCurrentPageBookExercises)
            {
                if (x.AssignmentCode == 0 && x.Id == 0)
                {
                    lstCurrentPageLeftButton1Excersices.Add(x);
                }
                if (x.AssignmentCode == 0 && x.Id == 1)
                {
                    lstCurrentPageLeftButton2Excersices.Add(x);
                }
                if (x.AssignmentCode == 0 && x.Id == 2)
                {
                    lstCurrentPageLeftButton3Excersices.Add(x);
                }
                if (x.AssignmentCode == 0 && x.Id == 3)
                {
                    lstCurrentPageLeftButton4Excersices.Add(x);
                }
            }
            if (lstCurrentPageLeftButton1Excersices.Count > 0)
            {
                btn1SpecialPages.DataContext = lstCurrentPageLeftButton1Excersices.ElementAt(0);
            }
            if (lstCurrentPageLeftButton2Excersices.Count > 0)
            {
                btn2SpecialPages.DataContext = lstCurrentPageLeftButton2Excersices.ElementAt(0);
                btn2SpecialPages.Visibility = Visibility.Visible;
                btn2Line.Visibility = Visibility.Visible;

            }
            else
            {
                btn2SpecialPages.Visibility = Visibility.Collapsed;
                btn3SpecialPages.Visibility = Visibility.Collapsed;
                btn4SpecialPages.Visibility = Visibility.Collapsed;
                btn2Line.Visibility = Visibility.Collapsed;
                btn3line.Visibility = Visibility.Collapsed;
                btn4line.Visibility = Visibility.Collapsed;

            }
            if (lstCurrentPageLeftButton3Excersices.Count > 0)
            {
                btn3SpecialPages.DataContext = lstCurrentPageLeftButton3Excersices.ElementAt(0);
                btn3SpecialPages.Visibility = Visibility.Visible;
                btn3line.Visibility = Visibility.Visible;
            }
            else
            {
                btn3SpecialPages.Visibility = Visibility.Collapsed;
                btn4SpecialPages.Visibility = Visibility.Collapsed;
                btn3line.Visibility = Visibility.Collapsed;
                btn4line.Visibility = Visibility.Collapsed;
            }
            if (lstCurrentPageLeftButton4Excersices.Count > 0)
            {
                btn4SpecialPages.DataContext = lstCurrentPageLeftButton4Excersices.ElementAt(0);
                btn4SpecialPages.Visibility = Visibility.Visible;
                btn4line.Visibility = Visibility.Visible;
            }
            else
            {
                btn4SpecialPages.Visibility = Visibility.Collapsed;
                btn4line.Visibility = Visibility.Collapsed;
            }


            GridSectionTitle.DataContext = null;
            GridSectionTitle.DataContext = currentPageSettings;
        }


    }

Answer 1

如果未选择任何项目，则gvSpecialPagesViewExercise.SelectedIndex将为-1，这是ElementAt的无效值。

在切换之前添加处理程序以防止该异常：

if(gvSpecialPagesViewExercise.SelectedIndex <= 0)
   return;

Answer 2

虽然没有回答你的问题（显然你同时发现了这个问题），但这里有一些提示：

您的代码看起来非常复杂，因为您正在单独处理这四个列表。如果将它们放在数组中，则可以全局处理它们，从而简化代码。

List<BookExercises>[] exercises = new List<BookExercises>[4];

private void UpdateLeftButtonContent()
{
    ResetSpecialPagesButtonColors();
    if (currentPageSettings.PageStyle.Contains("Especiales")) {
        for (int i = 0; i < exercises.Length; i++) {
            exercises[i] = new List<BookExercises>();
        }
        foreach (BookExercises x in lstCurrentPageBookExercises) {
            if (x.AssignmentCode == 0 && x.Id >= 0 && x.Id < exercises.Length) {
                exercises[x.Id].Add(x);
            }
        }
        ...
    }
}

int specialbtnId = 0;
private void gvSpecialPagesViewExercise_SelectionChanged(object sender,
    SelectionChangedEventArgs e)
{  
    // If you are sure that this condition is always true, you can drop it.
    if (specialbtnId >= 0 && specialbtnId < exercises.Length) {
        BookExercises lst = exercises[specialbtnId];
        int index = gvSpecialPagesViewExercise.SelectedIndex;
        if (index >= 0 && index < lst.Count) {
            LoadSpecialPagesBookExcersices(lst[index]);
        }
    }
}

C＃选择更改索引超出范围

2 个答案: