当我使用comboBoxCities.Visibility = System.Windows.Visibility.Hidden时,为什么程序会崩溃; [英] Why does my program crash when I use comboBoxCities.Visibility = System.Windows.Visibility.Hidden;
问题描述
你好
我有一个组合框,我有一个名为 comboBoxCountry_SelectionChanged的事件,当我将以下代码添加到程序崩溃时,当它试图启动时" comboBoxCities.Visibility = System.Windows.Visibility.Hidden;"
I have a combobox and I have an event for it called comboBoxCountry_SelectionChanged when I add the following code to event the program crashes when its trying to start "comboBoxCities.Visibility = System.Windows.Visibility.Hidden;"
我已粘贴下面的c#和xaml代码
I have pasted the c# and xaml code below
C#代码
private void comboBoxCountry_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
comboBoxCities.Visibility = System.Windows.Visibility.Hidden;
labelCity.Visibility = System.Windows.Visibility.Hidden;
if (comboBoxCountry.SelectedItem.ToString().Contains("United States"))
{
comboBoxCities.Visibility = System.Windows.Visibility.Visible;
labelCity.Visibility = System.Windows.Visibility.Visible;
}
else if (comboBoxCountry.SelectedItem.ToString().Contains("Canada"))
{
comboBoxCities.Visibility = System.Windows.Visibility.Visible;
labelCity.Visibility = System.Windows.Visibility.Visible;
}
}
推荐答案
我看到它已经有一段时间了,因为这是发布了,你可能已经修好了。 如果没有,问题是comboBoxCities最初为null。 所以先做一个空检查。
I see it has been awhile since this was posted, and you probably have fixed this already. If not, the problem is that the comboBoxCities is null initially. So just do a null check first.
private void comboBoxCountry_SelectionChanged(object sender, SelectionChangedEventArgs e)
{
if (comboBoxCities == null)
return;
comboBoxCities.Visibility = System.Windows.Visibility.Hidden;
labelCity.Visibility = System.Windows.Visibility.Hidden;
if (comboBoxCountry.SelectedItem.ToString().Contains("United States"))
{
comboBoxCities.Visibility = System.Windows.Visibility.Visible;
labelCity.Visibility = System.Windows.Visibility.Visible;
}
else if (comboBoxCountry.SelectedItem.ToString().Contains("Canada"))
{
comboBoxCities.Visibility = System.Windows.Visibility.Visible;
labelCity.Visibility = System.Windows.Visibility.Visible;
}
}
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