Question

我有一个名为cmbSubjects的组合框。我的项目的目的是在测验竞赛中改变主题。我希望在更改所选项目时，如果在更改前组合框中有关于主题的未答复问题，则消息框应询问测验主机是否确定是否继续。如果他们回答“否”，则组合框应选择其先前选择的项目。我得到了这个代码，但问题是如果quix master在消息框中选择NO，则消息框会出现两次。我发现原因（在从断点进入代码之后）是当消息框返回NO时，我的代码将组合框的选定值更改为其先前的值，这会触发cmbSubjects_SelectedIndexChanged事件。我尝试通过添加一个变量来修改代码，以计算消息框出现的次数以防止它。问题是它只在首次更改组合框的值后出现。下面的代码实际上是修改后的代码。谁能帮我这个？提前致谢。（我正在使用C＃）

private void cmbSubjects_SelectedIndexChanged(object sender, EventArgs e)
    {
        if (pnlAvailable.Controls.Count != 0)
        {
            if (countMsg < 1)
            {
                DialogResult res = MessageBox.Show("There are still available questions. Are you sure you want to change the subject?", "Changing subject...", MessageBoxButtons.YesNo, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1);
                if (res == DialogResult.Yes)
                {
                    cmbIndex = cmbSubjects.SelectedIndex;
                    countMsg = 0;
                    switch (cmbSubjects.SelectedIndex)
                    {
                        case 0:
                            subject = "life";
                            break;
                        case 1:
                            subject = "math";
                            break;
                        case 2:
                            subject = "physical";
                            break;
                        case 3:
                            subject = "technology";
                            break;
                        case 4:
                            subject = "vocational";
                            break;
                    }

                    GenQstBtns();
                }
                else if (res == DialogResult.No)
                {
                    countMsg = 1;
                    cmbSubjects.SelectedIndex = cmbIndex;
                }
            }
        }
    }

Answer 1

您可以使用SelectionChangeCommitted活动。

不要使用SelectedIndexChanged或SelectedValueChanged来捕获用户更改，因为当选择以编程方式更改时也会引发这些事件。

因此，如果您在以编程方式更改所选项目后使用此事件，则此事件将不会再次触发

Answer 2

是否有可能有多个处理程序连接SelectedIndexChanged事件？您可以在调试器中查看附加到事件的所有处理程序。

Answer 3

只需针对当前保存的索引检查新索引：

private void cmbSubjects_SelectedIndexChanged(object sender, EventArgs e)
{
    if (pnlAvailable.Controls.Count != 0)
    {
        if (cmbSubjects.SelectedIndex != cmbIndex)
        {
            DialogResult res = MessageBox.Show("There are still available questions. Are you sure you want to change the subject?", "Changing subject...", MessageBoxButtons.YesNo, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1);
            if (res == DialogResult.Yes)
            {
                cmbIndex = cmbSubjects.SelectedIndex;
                switch (cmbSubjects.SelectedIndex)
                {
                    case 0:
                        subject = "life";
                        break;
                    case 1:
                        subject = "math";
                        break;
                    case 2:
                        subject = "physical";
                        break;
                    case 3:
                        subject = "technology";
                        break;
                    case 4:
                        subject = "vocational";
                        break;
                }

                GenQstBtns();
            }
            else if (res == DialogResult.No)
            {
                cmbSubjects.SelectedIndex = cmbIndex;
            }
        }
    }
}

Answer 4

手动更改时，需要禁止触发IndexChanged事件。

您可以停用该活动：

            else if (res == DialogResult.No)
            {
                countMsg = 1;

                cmbSubjects.SelectedIndexChanged -= cmbSubjects_SelectedIndexChanged;
                cmbSubjects.SelectedIndex = cmbIndex;
                cmbSubjects.SelectedIndexChanged += cmbSubjects_SelectedIndexChanged;

                fireEvent = true;
            }

Answer 5

如果我正确理解你要做什么，最简单的事情可能是添加一个bool变量executionSelectedIndexChanged初始化为false。在您的方法中，您可以检查此bool，如果为false，则将其设置为true并打开您的MessageBox。如果答案是肯定的话，你再次将它设置为假。如果在方法开头bool为yes，只需将其设置为false并返回：

private bool executingSelectedIndexChanged  = false;
private void cmbSubjects_SelectedIndexChanged(object sender, EventArgs e)
{
    // NEW CODE HERE
    if (executingSelectedIndexChanged)
    {
        executingSelectedIndexChanged = false;
        return;
    }

    if (pnlAvailable.Controls.Count != 0)
    {
        if (countMsg < 1)
        {

            // NEW CODE HERE
            executingSelectedIndexChanged  = true;

            DialogResult res = MessageBox.Show("There are still available questions. Are you sure you want to change the subject?", "Changing subject...", MessageBoxButtons.YesNo, MessageBoxIcon.Exclamation, MessageBoxDefaultButton.Button1);
            if (res == DialogResult.Yes)
            {
                // NEW CODE HERE
                executingSelectedIndexChanged = false;

                cmbIndex = cmbSubjects.SelectedIndex;
                countMsg = 0;
                switch (cmbSubjects.SelectedIndex)
                {
                    case 0:
                        subject = "life";
                        break;
                    case 1:
                        subject = "math";
                        break;
                    case 2:
                        subject = "physical";
                        break;
                    case 3:
                        subject = "technology";
                        break;
                    case 4:
                        subject = "vocational";
                        break;
                }

                GenQstBtns();
            }
            else if (res == DialogResult.No)
            {
                countMsg = 1;
                cmbSubjects.SelectedIndex = cmbIndex;
            }
        }
    }
}

Messagebox出现两次C＃

5 个答案: