CODEWITHSUNDEEP
c#uwpwindows-iot-core-10
mylim
mylim

Reputation: 313

UWP C# System.InvalidCastException

I have previously asked on a post regarding how to dynamically add buttons. Now I have added additional image beside the button to indicate the connection status of the client(s). I have 2 buttons one to add and another to delete the button and image. Once clicked there will be a menuflyout to select the respective button to be deleted. My problem is I manage to add the status image but when comes to clicking at the delete button, the menuflyout runs into exception which says System.InvalidCastException.

My code as follow; please help. Thanks.

public Uri connectedUri = new Uri("ms-appx:///Assets/icon-connected.png");
public Uri disconnectedUri = new Uri("ms-appx:///Assets/icon-disconnected.png");

private void AddMenuFlyoutItem_Click(object sender, RoutedEventArgs e)
{
    var item = sender as MenuFlyoutItem;
    var deviceName = item.Text;
    var deviceIP = item.Tag;

    Button b = new Button();
    b.Height = 30;
    b.Width = 100;
    b.VerticalAlignment = VerticalAlignment.Top;
    b.HorizontalAlignment = HorizontalAlignment.Left;
    b.Margin = new Thickness(20, 20, 0, 0);
    b.Content = deviceName;   // "Button " + buttonCounter;
    b.Tag = deviceIP;
    b.Click += AddMenuButton_Click;


    Image stsImg = new Image();
    BitmapImage bitmapImage = new BitmapImage();
    //Uri connectedUri = new Uri("ms-appx:///Assets/icon-connected");
    //Uri disconnectedUri = new Uri("ms-appx:///Assets/icon-disconnected");
    bitmapImage.UriSource = connectedUri;
    stsImg.Source = bitmapImage;
    stsImg.Width = 20;
    stsImg.Height = 20;
    stsImg.VerticalAlignment = VerticalAlignment.Top;
    stsImg.HorizontalAlignment = HorizontalAlignment.Left;
    stsImg.Margin = new Thickness(130, 20, 0, 0);
    stsImg.Name = deviceName;
    stsImg.Tag = deviceIP;

    //Calculate the place of the button
    int column = (int)(buttonCounter / 4);
    int row = buttonCounter % 4;

    //Check if you need to add a columns
    if (row == 0)
    {
        ColumnDefinition col = new ColumnDefinition();
        col.Width = new GridLength(column, GridUnitType.Auto);
        myGrid.ColumnDefinitions.Add(col);
    }

    //Add the button
    myGrid.Children.Add(b);
    Grid.SetColumn(b, column);
    Grid.SetRow(b, row);

    myGrid.Children.Add(stsImg);
    Grid.SetColumn(stsImg, column);
    Grid.SetRow(stsImg, row);
    buttonCounter++;
}

private void RemoveButton_Click(object sender, RoutedEventArgs e)
{
    var menuFlyout = new MenuFlyout();

    try
    {
        foreach (Button btn in myGrid.Children)
        {
            var row = Grid.GetRow(btn);
            var col = Grid.GetColumn(btn);
            //ButtonRow.Add(btn.Content.ToString(), row.ToString());
            //ButtonCol.Add(btn.Content.ToString(), col.ToString());
            var menuFlyoutItem = new MenuFlyoutItem() { Name = btn.Tag.ToString(), Text = btn.Content.ToString() };
            menuFlyoutItem.Tag = btn.Content.ToString();
            menuFlyoutItem.Click += RemoveMenuFlyoutItem_Click;
            menuFlyout.Items.Add(menuFlyoutItem);
        }
        RemoveButton.Flyout = menuFlyout;
    }
    catch (Exception)
    {

    }
}

Upvotes: 0

Views: 164

Answers (2)

kkica
kkica

Reputation: 4104

Are all the children of myGrid, of Type Button?

 foreach (Button btn in myGrid.Children)

No, because myGrid.Children.Add(stsImg);

When you try to get stsImg as a Button, you have that exception, because stsImg is not of type Button.

You need to filter only the buttons.

foreach (Button btn in myGrid.Children.OfType<Button>()){
// do stuff
}

Upvotes: 1

Martin Zikmund
Martin Zikmund

Reputation: 39072

The problem is the foreach:

foreach (Button btn in myGrid.Children)

When written like this, it tries to cast all children of the Grid to Button. This is not possible, because some of the children are not buttons. You can however write the loop like this:

foreach (Button btn in myGrid.Children.OfType<Button>())

The OfType<T> LINQ extension method will filter the input enumerable only to those items which are of a given type.

Upvotes: 5

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