如何在lambda方法中传递参数和async关键字？

Question

如何在此代码中传递framworkElement并使用async关键字？

SaveImage = new RelayCommand<FrameworkElement>(frameworkElementForPrint =>  
{
    StorageFile file = await PickImageFileToSave();
    SaveVisualElementToFile(frameworkElementForPrint, file);
});

现在等待不能用......

Answer 1

我建议您将所有逻辑分解为单独的方法,如下所示:

public async Task SaveImageAsync(FrameworkElement frameworkElementForPrint)
{
  StorageFile file = await PickImageFileToSaveAsync();
  await SaveVisualElementToFileAsync(frameworkElementForPrint, file);
}

然后将其包装成RelayCommand:

SaveImage = new RelayCommand<FrameworkElement>(async arg => { await SaveImageAsync(arg); });

这种分离允许您对SaveImageAsync逻辑进行单元测试(当然假设您使用适当的抽象进行重构).

这篇MSDN文章有关于async命令的更多细节.