Xamarin Forms DependencyService nullReferenceException

Question

我正在尝试从手机图库添加图像，但不断获取 System.Reference，并且我想在按下按钮时从手机图库上传图像，并且它在 DependencyService 上给出 nullReferenceException。

我的页面：

InitializeComponent();


        Device.OnPlatform(
            Android: () => {
                new Thickness(0, 20, 0, 0);
                }
        );

        Image image = new Image();

        Button addImage = new Button { Text = "Select Image" };
        addImage.Clicked += (sender, args) =>
        {
            IGalleryImageService galleryService = DependencyService.Get<IGalleryImageService>();
            galleryService.ImageSelected += (o, imageSourceEventArgs) => image.Source = imageSourceEventArgs.ImageSource;
            galleryService.SelectImage();

        };

        this.Content = new StackLayout
        {
            Children =
            {
                image,
                addImage
            }
        };

Answer 1

您可能忘记通过添加正确的属性来导出实现。

您在文件中的名称空间声明上方是否有此内容GalleryImageService_Android.cs？

[assembly: Xamarin.Forms.Dependency (typeof (GalleryImageService_Android))]