c# - 为什么我收到 FormatException 是未处理的错误？

Question

我创建了一个程序，并对其进行了广泛的测试，我收到一条错误消息，提示“FormatException 未处理，输入字符串的格式不正确”。当我将任一文本框留空并按下“完成”按钮时会出现问题，但如果我输入低于 0 或高于 59 的任何内容，它会正常工作——这是我想要允许的数字范围。我该怎么做才能在方框为空时不收到此错误消息？这是我在“btnFinished”背后的代码:

   private void btnFinished_Click(object sender, EventArgs e)
    {
        if (lstCyclists.SelectedIndex >= 0)
        {
            Cyclists currentCyc = (Cyclists)lstCyclists.SelectedItem;
            //Decalre the minsEntered and secsEntered variables for txtMins and textSecs
            int minsEntered = int.Parse(txtMins.Text);
            int secsEntered = int.Parse(txtSecs.Text);

            try
            {
                //If the status of a cyclist is already set to Finished, show an error
                if (currentCyc.Finished.ToString() == "Finished")
                {
                    MessageBox.Show("A time has already been entered for this cyclist");
                }
                else
                {
                    //if a minute lower than 0 or greater than 59 has been entered, show an error
                    if (minsEntered < 0 || minsEntered > 59)
                    {
                        MessageBox.Show("You can only enter a minute up to 59");
                    }
                    //if a second lower than 0 or greater than 59 has been entered, show an error
                    else if (secsEntered < 0 || secsEntered > 59)
                    {
                        MessageBox.Show("You can only enter a second up to 59");
                    }
                    else
                    {
                        //otherwise, set the status to finished and update the time
                        currentCyc.Finished = "Finished";
                        currentCyc.FinishedHours(Convert.ToInt32(txtHours.Text));
                        currentCyc.FinishedMins(Convert.ToInt32(txtMins.Text));
                        currentCyc.FinishedSecs(Convert.ToInt32(txtSecs.Text));
                        //pass the parameter to the scoreboard class to display it in lblCyclistsFinished
                        lblCyclistsFinished.Text += "\n" + finishLine.Scoreboard(currentCyc);
                        //add to the number of cyclists finished
                        Cyclists.NumFinished++;
                        lblnumFinished.Text = Cyclists.NumFinished.ToString();
                        //update the details box
                        DisplayDetails(currentCyc);
                        txtHours.Clear();
                    }
                }
            }
            catch
            //make sure all the time fields have been entered, otherwise show an error message
            {
                MessageBox.Show("Please ensure all time fields have been entered");
            }
        }
        else
            //make sure a cyclist has been selected when pressing "Finished", otherwise show an error message
        {
            MessageBox.Show("You must select a cyclist");
        }
    }

Answer 1

好吧，看看这些行:

int minsEntered = int.Parse(txtMins.Text);
int secsEntered = int.Parse(txtSecs.Text);

当文本框为空白时，您期望返回什么？

不要为空文本框调用 int.Parse。例如:

int minsEntered = txtMins.Text == "" ? 0 : int.Parse(txtMins.Text);
// Ditto for seconds

当然，如果您输入非数字内容，这仍然会出错。您可能应该改用 int.TryParse:

int minsEntered;
int.TryParse(txtMins.Text, out minsEntered);

在这里，我忽略了 TryParse 的结果，并且无论如何它都会将 minsEntered 保留为 0 - 但如果您想要不同的默认值，您可以使用类似:

int minsEntered;
if (!int.TryParse(txtMins.Text, out minsEntered))
{
    minsEntered = 5; // Default on parsing failure
}

(或者您可以在这种情况下显示错误消息...)