XamariniForms，拍照，发生未处理的异常

Question

I would like to take one photo at Xamarin.Forms. But when I build it, when I click on the "Take Photo" button I get the above error. I put a breakpoint on all lines, but I could not find my fault.

Click Take Photo

ResimYukle.axml.cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

using Xamarin.Forms;
using Xamarin.Forms.Xaml;
using hackathon.CustomControls;
using hackathon.Views;
using Plugin.Media;
namespace hackathon.TabbedPages
{
    [XamlCompilation(XamlCompilationOptions.Compile)]
    public partial class ResimYukle : ContentPage
    {
        private Image img;

        public ResimYukle()
        {
            InitializeComponent();
            RelativeLayout layout = new RelativeLayout();
            CustomButton btnTakePhoto = new CustomButton
            {
                Text = "Take Photo"
            };
            btnTakePhoto.Clicked += BtnTakePhoto_Clicked;

            CustomButton btnPickPhoto = new CustomButton
            {
                Text = "Pick Photo"
            };
            btnPickPhoto.Clicked += BtnPickPhoto_Clicked;
            CustomButton btnTakeVideo = new CustomButton
            {
                Text = "Take Video"
            };
            btnTakeVideo.Clicked += BtnTakeVideo_Clicked;
            CustomButton btnPickVideo = new CustomButton
            {
                Text = "Pick Vİdeo"
            };
            btnPickVideo.Clicked += BtnPickVideo_Clicked;

            StackLayout stkImage = new StackLayout
            {
                BackgroundColor = Color.White
            };
            img = new Image
            {
                Source = "defaultimg.png"
            };
            stkImage.Children.Add(img);

            layout.Children.Add(stkImage, Constraint.Constant(0),
                Constraint.Constant(0), Constraint.RelativeToParent(
                    (parent) =>
                    {
                        return parent.Width;
                    }));

            StackLayout stkPictureButtons = new StackLayout
            {
                Orientation = StackOrientation.Horizontal,
                HorizontalOptions = LayoutOptions.FillAndExpand,
                Padding = 20,
                Children =
                {
                    btnTakePhoto,
                    btnPickPhoto
                }
            };
            StackLayout stkVideoButtons = new StackLayout
            {
                Orientation = StackOrientation.Horizontal,
                HorizontalOptions = LayoutOptions.FillAndExpand,
                Padding = 20,
                Children =
                {
                    btnTakeVideo,
                    btnPickVideo,
                }
            };

            layout.Children.Add(stkPictureButtons, Constraint.Constant(0),
                Constraint.Constant(0), Constraint.RelativeToParent((parent) =>
                {
                    return parent.Width;
                }));

            layout.Children.Add(stkVideoButtons, Constraint.Constant(0),
                Constraint.RelativeToView(stkPictureButtons,
                (parent, sibling) =>
                {
                    return sibling.Height + 10;
                }), Constraint.RelativeToParent((parent) =>
                {
                    return parent.Width;
                }));

            Content = layout;
        }

        private async void BtnPickVideo_Clicked(object sender, EventArgs e)
        {
            if (!CrossMedia.Current.IsPickVideoSupported)
            {
                DisplayAlert("UYARI", "Galeriye erişme yetkiniz yok!", "OK");
                return;
            }
            var file = await CrossMedia.Current.PickVideoAsync();

            if (file == null)
                return;

            DisplayAlert("UYARI", "Seçilen video: " + file.Path, "OK");
            file.Dispose();
        }

        private async void BtnTakeVideo_Clicked(object sender, EventArgs e)
        {
            if (!CrossMedia.Current.IsCameraAvailable || !CrossMedia.Current.IsTakeVideoSupported)
            {
                DisplayAlert("UYARI", "Cihazınızın kamerası aktif değil!", "OK");
                return;
            }

            var file = await CrossMedia.Current.TakeVideoAsync(
                new Plugin.Media.Abstractions.StoreVideoOptions
                {
                    Name = DateTime.Now + ".mp4",
                    Directory = "MediaPluginPhotoVideo",
                    Quality = Plugin.Media.Abstractions.VideoQuality.High,
                    DefaultCamera = Plugin.Media.Abstractions.CameraDevice.Front
                });

            if (file == null)
                return;

            DisplayAlert("UYARI",
                "Video başarılı bir şekilde kayıt edildi: " + file.Path, "OK");

            file.Dispose();
        }

        private async void BtnPickPhoto_Clicked(object sender, System.EventArgs e)
        {
            if (!CrossMedia.Current.IsPickPhotoSupported)
            {
                DisplayAlert("UYARI", "Galeriye erişme yetkiniz yok!", "OK");
                return;
            }
            var file = await CrossMedia.Current.PickPhotoAsync();

            if (file == null)
                return;

            img.Source = ImageSource.FromStream(() =>
            {
                var stream = file.GetStream();
                file.Dispose();
                return stream;
            });
        }

        private async void BtnTakePhoto_Clicked(object sender, System.EventArgs e)
        {
            int a;

            if (!CrossMedia.Current.IsCameraAvailable || !CrossMedia.Current.IsTakePhotoSupported)
            {
                a = 0;
                int b;
                DisplayAlert("UYARI", "Cihazınızın kamerası aktif değil!", "OK");
                b = 0;
                return;
            }

            var file = await CrossMedia.Current.TakePhotoAsync(
                new Plugin.Media.Abstractions.StoreCameraMediaOptions
                {
                    Directory = "MediaPluginPhoto",
                    Name = DateTime.Now + ".jpg",
                    DefaultCamera = Plugin.Media.Abstractions.CameraDevice.Front
                });

            if (file == null)
                return;

            img.Source = ImageSource.FromStream(() =>
            {
                var stream = file.GetStream();
                file.Dispose();
                return stream;
            });
        }
    }
}

ResimYukle.axml

<?xml version="1.0" encoding="utf-8" ?>
<ContentPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             x:Class="hackathon.TabbedPages.ResimYukle"
             Title="Yükle">
</ContentPage>

I do this by looking at my example from here : https://github.com/ozaksuty/Xamarin-Ogreniyorum/tree/master/MediaPlugin

Answer 1

For future reference I will take the answer of apineda in the comments and elaborate a bit.

The error here is that you have installed the NuGet package only on your shared PCL project. What you need to do is install it on your PCL project as well as your platform projects .

This is because of the way these plugins and Xamarin.Forms work. What actually happens with plugins like these is it offers you an abstract method to work with. Xamarin.Forms is targeting multi-platform, but at the end of the day, it will just transform into a native app. Because of that, it needs an implementation on the actual platform. For this example, code for showing the camera differs greatly between Android and iOS (and all other platforms for that matter).

So, effectively, you are installing the plugin on your shared library to get the method you call upon, but it is not implemented. By then installing the same plugin (but it takes another binary) to your platform project(s), the method will get it's implementation.

It is kind of hard to determine whether a plugin needs to be installed on all projects, or just the shared. Try to decide for yourself if it uses any platform specific stuff.