在選擇更改時設置TextBlock可見性

Question

目前，我有一個組合框，並且想要更改某些選擇上TextBlock的可見性。

錯誤，產生的Object reference not set to an instance of an object.

private void Selection(object sender, SelectionChangedEventArgs e)
{
    if (Findpf() == 12)
    {
        DateAutoCompleteBox.Visibility = System.Windows.Visibility.Collapsed;
    }
    else
    {
        DateAutoCompleteBox.Visibility = System.Windows.Visibility.Visible;
    }
}

嘗試= Visibility.Collapsed也折疊，結果相同。 我該如何解決 ？

public uint Findpf()
{
    if (Pf.Text == "Annual")
    {
        return 1;
    }
    if (Pf.Text == "Semi-annual")
    {
        return 2;
    }
    if (Pf.Text == "Tri-Annual")
    {
        return 3;
    }
    if (Pf.Text == "Quarterly")
    {
        return 4;
    }
   if (Pf.Text == "Bi-Monthly")
    {
        return 6;
    }
     if (Pf.Text == "Monthly")
    {
         return 12;
    }
}

Autocompletebox Xaml的初始化

<telerik:RadAutoCompleteBox x:Name="DateAutoCompleteBox" Visibility="Visible" Width="220"></telerik:RadAutoCompleteBox>

Answer 1

您可以嘗試檢查此值是否為空

private void Selection(object sender, SelectionChangedEventArgs e)
{
    if(DateAutoCompleteBox == null)
    {
        MessageBox.Show("DateAutoCompleteBox   is null"); return;
    }
    if(Pf == null)
    {
        MessageBox.Show("Pf  is null"); return;
    }
    if(Pf.Text == null)
    {
        MessageBox.Show("Pf.Text  is null"); return;
    }
    if (Findpf() == 12)
    {
        DateAutoCompleteBox.Visibility = System.Windows.Visibility.Collapsed;
    }
    else
    {
        DateAutoCompleteBox.Visibility = System.Windows.Visibility.Visible;
    }
}

Answer 2

DateAutoCompleteBox設置為null，您不能訪問或設置未初始化對象的屬性。