How do I initialize a CompositionTarget to null using the Rust Crate for Windows?

user_15953146 0
Viewed 69

Specifically, what is the correct way to initialize the CompositionTarget member in the following Rust Crate for Windows CoreApp code excerpt?

#[implement(Windows::ApplicationModel::Core::IFrameworkView)]
struct AppView {
    target: CompositionTarget,
}
        
#[allow(non_snake_case)]
impl AppView {
    fn new() -> Self { //
        Self {
            //target: std::ptr::null_mut(),
            //target: CompositionTarget(0),
        }
    }
      
    fn Initialize(&self, _: &Option<CoreApplicationView>) -> Result<()> {
        Ok(())
    }
        
    fn Load(&self, _: &HSTRING) -> Result<()> {
        Ok(())
    }
        
    fn Uninitialize(&self) -> Result<()> {
        Ok(())
    }
      
    fn Run(&self) -> Result<()> {
        let window = CoreWindow::GetForCurrentThread()?;
        window.Activate()?;
      
        let dispatcher = window.Dispatcher()?;
        dispatcher.ProcessEvents(CoreProcessEventsOption::ProcessUntilQuit)?;

        Ok(())
    }
        
    fn SetWindow(&self, _: &Option<CoreWindow>) -> Result<()> {
        let compositor = Compositor::new()?;
        let root = compositor.CreateContainerVisual()?;
        //...
        Ok(())
    }
}
        
fn main() -> Result<()> {
    unsafe {
        CoInitializeEx(std::ptr::null_mut(), COINIT_MULTITHREADED)?;
    }
       
    let app: IFrameworkViewSource = App().into();
    CoreApplication::Run(app)?;
    Ok(())
}
rust windows
1 Answers

Rust does not have null. Instead, you should use Option:

struct AppView {
    target: Option<CompositionTarget>,
}

impl AppView {
    fn new() -> Self {
        Self {
            target: None,
        }
    }
    ...

This works well since in the windows crate a CompositionTarget cannot be null, any function that would return a null value will return an Option::None or Err(Error::Ok) instead. See this issue.

user_21891300
Related