"Input String is not in Correct Format" withTextbox Selection Changed 事件

Question

private void txtdiscount_SelectionChanged(object sender, RoutedEventArgs e)
{
    try
    {
        string dis = txtdiscount.Text.ToString();
        double isid = double.Parse(dis);

        isid = isid + 10;

        MessageBox.Show(isid.ToString());

    }
    catch (Exception exp)
    {
        MessageBox.Show(exp.ToString());
    }
}

我想在文本框 txtdiscount 和文本框的 SelectionChanged 事件中输入（双精度类型），MessageBox 应该在增量 10 后显示输入的值它的价值。但是使用上面的代码，我得到一个例外：

"Input String was not correct format"

行：

string dis = txtdiscount.Text.ToString()

文本框 SelectionChanged 事件中的这段代码有什么问题，因为在按钮单击事件中执行相同的代码可以正常工作？

 <TextBox  x:Name="txtdiscount" HorizontalAlignment="Left" Height="33" Margin="831,97,0,0" TextWrapping="Wrap" VerticalAlignment="Top" Width="154" SelectionChanged="txtdiscount_SelectionChanged"/>

Answer 1

Use Double.TryParse() & instead of SelectionChanged use TextChanged event.

As per MSDN

SelectionChanged :- This event occurs whenever there is a change to a selection. A selection can be changed not only by user interaction but also by binding as well as other set values.

TextChanged :- This event is raised if the Text property is changed by either a programmatic modification or user interaction.

 string dis = txtBox.Text;
 double isId;
 if (Double.TryParse(dis, out isId))
 {
      isId = isId + 10;
      MessageBox.Show(isId.ToString());
 }
 else
 {
    MessageBox.Show("Please Only enter Number");
 }

Answer 2

您的问题是 SelectionChanged 事件在您单击 TextBox 时立即触发。此时内部没有值，所以 double.Parse() 得到一个空字符串作为输入并抛出这个异常。当您从 TextBox.

中删除最后一位数字时，它也会抛出异常

要解决这种情况，您可以检查空值：

private void txtdiscount_SelectionChanged(object sender, RoutedEventArgs e)
{
    try
    {
        if (!string.IsNullOrWhiteSpace(txtdiscount.Text))
        {

            string dis = txtdiscount.Text;
            double isid = double.Parse(dis);

            isid = isid + 10;

            MessageBox.Show(isid.ToString());
        }

    }
    catch (Exception exp)
    {
        MessageBox.Show(exp.ToString());
    }
}

same code works fine when performed in a button click event

因为你在输入有效值后点击。这就是区别

"Input String is not in Correct Format" withTextbox Selection Changed 事件

"Input String is not in Correct Format" withTextbox Selection Changed Event

c#

format

wpf

textbox