为什么我得到一个FormatException是未处理的错误？

Question

我已经创建了一个程序,并对它进行了大量测试,我收到一条错误消息"FormatException未处理,输入字符串格式不正确".当我将任一文本框留空并按下"完成"按钮但如果我输入低于0或高于59的任何值 - 这是我想要允许的数字范围,它会正常工作.我怎么办？当盒子空白时,我没有收到这个错误？这是'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,您希望那些人返回什么？

只是不要求int.Parse空文本框.例如:

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

当然,如果你输入非数字的东西,这仍然会爆炸.您可能应该使用int.TryParse:

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

在这里我忽略了结果TryParse,并且它将保留minsEntered为0 - 但如果你想要一个不同的默认值,你会使用类似的东西:

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

(或者你可以在这种情况下显示错误信息...)