如何使用 Windows 的 Rust 板条箱将 CompositionTarget 初始化为 null？

Question

具体来说，在以下 Windows CoreApp 代码摘录的 Rust Crate 中初始化 CompositionTarget 成员的正确方法是什么？

#[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(())
}

Answer 1

Rust 没有null 。 相反，您应该使用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. 看到这个问题。