Question

Why is my ApplicationBarIconButton null?

<phone:PhoneApplicationPage.ApplicationBar>
    <shell:ApplicationBar IsVisible="True" IsMenuEnabled="True" x:Name="appBar">
        <shell:ApplicationBarIconButton x:Name="appbarSave"
          IconUri="/Icons/appbar.save.rest.png Text="Save" IsEnabled="False"
          Click="appbarSave_Click" />
    </shell:Application Bar>
</phone:PhoneApplicationPage.ApplicationBar>

The appBarSave object is null, and trying this:

Initialize Component();
appbarSave.IsEnabled = true;

Results in a NullReferenceException. The only place the object works is in the click event (if I enable it):

private void appbarSave_Click(object sender, EventArgs e)
{
    ApplicationBarIconButton button = (ApplicationBarIconButton)sender;
    button.IsEnabled = false;
}

I would really like to be able to start the save button as disabled and enabled it later.

Answer 1

I remember running into this issue before: there’s an explanation here. An easy workaround is just to instantiate it in code-behind rather than xaml (like here).

private ApplicationBarIconButton SaveEdit;
private void InitAppBar()
{
     ApplicationBar appBar = new ApplicationBar();

     SaveEdit = new ApplicationBarIconButton(new Uri("images/appbar.check.rest.png", UriKind.Relative));
     SaveEdit.Click += new EventHandler(OnClick_Check);
     SaveEdit.Text = Strings.Save_button;
     appBar.Buttons.Add(SaveEdit);

     ApplicationBarIconButton CancelEdit = new ApplicationBarIconButton(new Uri("images/appbar.close.rest.png", UriKind.Relative));
     CancelEdit.Click += new EventHandler(OnClick_Cancel);
     CancelEdit.Text = Strings.Cancel_button;
     appBar.Buttons.Add(CancelEdit);

     ApplicationBar = appBar;
}