C# 使用Xamarin.Forms访问摄像头

是否有人能给出一个简短的、自包含的示例，说明如何使用Xamarin.Forms 1.3.x访问相机？只需调用本机相机应用程序并检索结果图片就可以了。在Xamarin.Forms页面上显示实时视图将非常棒

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我已经尝试过使用Xamarin.Mobile和Xamarin.Forms.Labs，但我无法在这两个平台上找到任何解决方案（目前专注于Android和iOS）。在web上找到的大多数代码片段（包括stackoverflow）都不完整，例如，没有显示IMedipicker对象的实现，也没有显示拍照方法的定位位置。

我终于为iOS和Android创建了一个最低限度的解决方案

共享项目 首先，让我们看看共享代码。为了方便共享的

应用程序

类和平台特定代码之间的交互，我们在

公共静态应用程序

中存储了一个静态

实例

：

公共静态应用实例；

此外，我们将显示一个

图像

，稍后将用内容填充该图像。因此，我们创建了一个成员：

readonly Image image = new Image();

在

应用程序

构造函数中，我们存储

实例

并创建页面内容，这是一个简单的

按钮

和前面提到的

图像

：

public App()
{
   Instance = this;

   var button = new Button {
       Text = "Snap!",
       Command = new Command(o => ShouldTakePicture()),
   };

   MainPage = new ContentPage {
       Content = new StackLayout {
       VerticalOptions = LayoutOptions.Center,
           Children = {
                    button,
                    image,
           },
       },
   };
}

按钮的单击处理程序调用事件

ShouldTakePicture

。 它是一个公共成员，平台特定的代码部分稍后将分配给它

public event Action ShouldTakePicture = () => {};

最后，我们提供了一种显示捕获图像的公共方法：

public void ShowImage(string filepath)
{
    image.Source = ImageSource.FromFile(filepath);
}

Android项目 在Android上，我们修改了

main活动

。 首先，我们为捕获的图像文件定义一个路径：

static readonly File file = new File(Environment.GetExternalStoragePublicDirectory(Environment.DirectoryPictures), "tmp.jpg");

在

OnCreate

的末尾，我们可以使用创建的

应用程序的静态
实例
，并分配一个匿名事件处理程序，它将启动一个新的
意图
来捕获图像：

App.Instance.ShouldTakePicture += () => {
   var intent = new Intent(MediaStore.ActionImageCapture);
   intent.PutExtra(MediaStore.ExtraOutput, Uri.FromFile(file));
   StartActivityForResult(intent, 0);
};

最后但并非最不重要的一点是，我们的活动必须对结果图像作出反应。它只需将其文件路径推送到共享的
ShowImage
方法

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
   base.OnActivityResult(requestCode, resultCode, data);
   App.Instance.ShowImage(file.Path);
}

就这样！
只是别忘了在“AndroidManifest.xml”中设置“Camera”和“WriteExternalStorage”权限

iOS项目
对于iOS实现，我们创建一个自定义渲染器。
因此，我们添加一个新文件“CustomContentPageRenderer”，并在using语句之后添加相应的程序集属性：

[assembly:ExportRenderer(typeof(ContentPage), typeof(CustomContentPageRenderer))]

CustomContentPageRenderer
继承自
PageRenderer
：

public class CustomContentPageRenderer: PageRenderer
{
    ...
}

我们覆盖了
viewdideappear
方法，并添加了以下部分

参照相机创建新的图像选择器控制器：

var imagePicker = new UIImagePickerController { SourceType = UIImagePickerControllerSourceType.Camera };

一旦引发
ShouldTakePicture
事件，立即显示图像选择器控制器：

App.Instance.ShouldTakePicture += () => PresentViewController(imagePicker, true, null);

拍照后，将其保存到
MyDocuments
文件夹，并调用共享
ShowImage
方法：

imagePicker.FinishedPickingMedia += (sender, e) => {
            var filepath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "tmp.png");
var image = (UIImage)e.Info.ObjectForKey(new NSString("UIImagePickerControllerOriginalImage"));
            InvokeOnMainThread(() => {
                image.AsPNG().Save(filepath, false);
                App.Instance.ShowImage(filepath);
            });
            DismissViewController(true, null);
        };

最后，我们需要处理图像拍摄过程的取消：

imagePicker.Canceled += (sender, e) => DismissViewController(true, null);

下面是如何在Xamarin窗体上跨Xamarin iOS执行此操作

这是一个很好的起点，但它需要先呈现一个页面，在该页面中，您可以为其指定UIView应用程序，以便为摄影机/照片拾取控制器提供UIView


可移植项目
公共接口ICameraProvider
{
Task TakePhotoAsync（）；
任务PickPhotoAsync（）；
}
私人司令部武官
{
var camera=wait DependencyService.Get（）.TakePhotoAsync（）；
}

iOS项目
[assembly:Xamarin.Forms.Dependency（typeof（CameraProvider））]
公共类摄像机提供者：ICameraProvider
{
专用UIImagePickerController\U imagePicker；
私人摄影师结果；
私有静态TaskCompletionSource\u tcs；
公共异步任务TakePhotoAsync（）
{
_tcs=新任务完成源（）；
_imagePicker=new UIImagePickerController{SourceType=UIImagePickerController源类型.Camera}；
_imagePicker.FinishedPickingMedia+=（发送方，e）=>
{
_结果=新摄像机结果（）；
var filepath=Path.Combine（Environment.GetFolderPath（Environment.SpecialFolder.MyDocuments），“tmp.png”）；
var image=（UIImage）e.Info.ObjectForKey（新NSString（“UIImagePickerControllerOriginalImage”）；
_result.ImageSource=ImageSource.FromStream（（）=>newmemoryStream（image.AsPNG（）.ToArray（））；
_result.ImageBytes=image.AsPNG（）.ToArray（）；
_result.FilePath=FilePath；
_tcs.TrySetResult（_result）；
_imagePicker.DismissViewController（true，null）；
};
_imagePicker.Cancelled+=（发送方，e）=>
{
UIApplication.SharedApplication.KeyWindow.RootViewController.DismissViewController（true，null）；
};
等待UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewControllerAsync（\u imagePicker，true）；
返回等待任务；
}
公共异步任务PickPhotoAsync（）
{
_tcs=新任务完成源（）；
_imagePicker=新UIImagePickerController
{
SourceType=UIImagePickerControllerSourceType.PhotoLibrary，
MediaTypes=UIImagePickerController.AvailableMediaTypes（UIImagePickerController源类型.PhotoLibrary）
};
_imagePicker.FinishedPickingMedia+=（发送方，e）=>
{
if（e.Info[UIImagePickerController.MediaType].ToString（）=“public.image”）
{
var filepath=（e.Info[新NSString（“UIImagePickerControllerReferenceUrl”）]作为NSUrl）；
var image=（UIImage）e.Info.ObjectForKey（新NSString（“UIImagePickerControllerOriginalImage”）；
//var image=e.Info[UIImagePickerController.OriginalImage]作为UIImage；
_result.ImageSource=ImageSource.FromStream（（）=>newmemoryStream（image.AsPNG（）.ToArray（））；
_result.ImageBytes=image.AsPNG（）.ToArray（）；
_result.FilePath=FilePath？.Pa
public interface ICameraProvider
{
    Task<CameraResult> TakePhotoAsync();
    Task<CameraResult> PickPhotoAsync();
}

private Command AttachImage 
{
    var camera = await DependencyService.Get<ICameraProvider>().TakePhotoAsync();
}

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

public class CameraProvider : ICameraProvider
{
    private UIImagePickerController _imagePicker;
    private CameraResult _result;
    private static TaskCompletionSource<CameraResult> _tcs;

    public async Task<CameraResult> TakePhotoAsync()
    {
        _tcs = new TaskCompletionSource<CameraResult>();

        _imagePicker = new UIImagePickerController { SourceType = UIImagePickerControllerSourceType.Camera };

        _imagePicker.FinishedPickingMedia += (sender, e) =>
        {
            _result = new CameraResult();
            var filepath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "tmp.png");
            var image = (UIImage)e.Info.ObjectForKey(new NSString("UIImagePickerControllerOriginalImage"));

            _result.ImageSource = ImageSource.FromStream(() => new MemoryStream(image.AsPNG().ToArray())); 
            _result.ImageBytes = image.AsPNG().ToArray();
            _result.FilePath = filepath;

            _tcs.TrySetResult(_result);
            _imagePicker.DismissViewController(true, null);
        };

        _imagePicker.Canceled += (sender, e) =>
        {
            UIApplication.SharedApplication.KeyWindow.RootViewController.DismissViewController(true, null);
        };

        await UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewControllerAsync(_imagePicker, true);

        return await _tcs.Task; 
    }

    public async Task<CameraResult> PickPhotoAsync()
    {
        _tcs = new TaskCompletionSource<CameraResult>();

        _imagePicker = new UIImagePickerController
        {
            SourceType = UIImagePickerControllerSourceType.PhotoLibrary,
            MediaTypes = UIImagePickerController.AvailableMediaTypes(UIImagePickerControllerSourceType.PhotoLibrary)
        };

        _imagePicker.FinishedPickingMedia += (sender, e) =>
        {

            if (e.Info[UIImagePickerController.MediaType].ToString() == "public.image")
            {
                var filepath = (e.Info[new NSString("UIImagePickerControllerReferenceUrl")] as NSUrl);
                var image = (UIImage)e.Info.ObjectForKey(new NSString("UIImagePickerControllerOriginalImage"));
                //var image = e.Info[UIImagePickerController.OriginalImage] as UIImage;

                _result.ImageSource = ImageSource.FromStream(() => new MemoryStream(image.AsPNG().ToArray()));
                _result.ImageBytes = image.AsPNG().ToArray();
                _result.FilePath = filepath?.Path;
            }

            _tcs.TrySetResult(_result);
            _imagePicker.DismissViewController(true, null);
        };

        _imagePicker.Canceled += (sender, e) =>
        {
            UIApplication.SharedApplication.KeyWindow.RootViewController.DismissViewController(true, null);
        };

        await UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewControllerAsync(_imagePicker, true);

        return await _tcs.Task;
    }
}

public async Task<string> TakePicture()
{
    if (await AuthorizeCameraUse())
    {
        var imagePicker = new UIImagePickerController { SourceType = UIImagePickerControllerSourceType.Camera };

        TaskCompletionSource<string> FinishedCamera = new TaskCompletionSource<string>();

        // When user has taken picture
        imagePicker.FinishedPickingMedia += (sender, e) => {
            // Save the file
            var filepath = Path.Combine(Environment.GetFolderPath(Environment.SpecialFolder.MyDocuments), "tmp.png");
            var image = (UIImage)e.Info.ObjectForKey(new NSString("UIImagePickerControllerOriginalImage"));
            image.AsPNG().Save(filepath, false);

            // Close the window
            UIApplication.SharedApplication.KeyWindow.RootViewController.DismissViewController(true, null);

            // Stop awaiting
            FinishedCamera.SetResult(filepath);
        };

        // When user clicks cancel 
        imagePicker.Canceled += (sender, e) =>
        {
            UIApplication.SharedApplication.KeyWindow.RootViewController.DismissViewController(true, null);
            FinishedCamera.TrySetCanceled();
        };

        // Show the camera-capture window
        UIApplication.SharedApplication.KeyWindow.RootViewController.PresentViewController(imagePicker, true, null);

        // Now await for the task to complete or be cancelled
        try
        {
            // Return the path we've saved the image in
            return await FinishedCamera.Task;
        }
        catch (TaskCanceledException)
        {
            // handle if the user clicks cancel
        }
    }

    return null;
}

public static async Task<bool> AuthorizeCameraUse()
{
    var authorizationStatus = AVCaptureDevice.GetAuthorizationStatus(AVMediaType.Video);

    if (authorizationStatus != AVAuthorizationStatus.Authorized)
    {
        return await AVCaptureDevice.RequestAccessForMediaTypeAsync(AVMediaType.Video);
    }
    else
        return true;
}

private TaskCompletionSource<bool> _tcs_NativeCamera;

public async Task<string> TakePicture()
{
    _tcs_NativeCamera = new TaskCompletionSource<bool>();

    // Launch the camera activity
    var intent = new Intent(MediaStore.ActionImageCapture);
    intent.PutExtra(MediaStore.ExtraOutput, Android.Net.Uri.FromFile(cameraCaptureFilePath));

    NextCaptureType = stype;

    StartActivityForResult(intent, SCAN_NATIVE_CAMERA_CAPTURE_ASYNC);

    // Wait here for the activity return (through OnActivityResult)
    var Result = await _tcs_NativeCamera.Task;

    // Return the camera capture file path
    return Result != Result.Canceled ? cameraCaptureFilePath : null;
}

protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
    base.OnActivityResult(requestCode, resultCode, data);

    switch (requestCode)
    {
        case SCAN_NATIVE_CAMERA_CAPTURE_ASYNC:
            _tcs_NativeCamera.SetResult(resultCode);
            break;
    }
}

public override void OnRequestPermissionsResult(int requestCode, string[] permissions, Permission[] grantResults)
{
    PermissionsImplementation.Current.OnRequestPermissionsResult(requestCode, permissions, grantResults);
}  

<provider android:name="android.support.v4.content.FileProvider" 
          android:authorities="YOUR_APP_PACKAGE_NAME.fileprovider" 
          android:exported="false" 
          android:grantUriPermissions="true">
    <meta-data android:name="android.support.FILE_PROVIDER_PATHS" 
               android:resource="@xml/file_paths"></meta-data>
</provider>

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path name="my_images" path="Android/data/YOUR_APP_PACKAGE_NAME/files/Pictures" />
    <external-path name="my_movies" path="Android/data/YOUR_APP_PACKAGE_NAME/files/Movies" />
</paths>

<key>NSCameraUsageDescription</key>
<string>This app needs access to the camera to take photos.</string>
<key>NSPhotoLibraryUsageDescription</key>
<string>This app needs access to photos.</string>
<key>NSMicrophoneUsageDescription</key>
<string>This app needs access to microphone.</string>

if (!CrossMedia.Current.IsCameraAvailable || !CrossMedia.Current.IsTakePhotoSupported)
{
    await DisplayAlert("No Camera", ":( No camera avaialble.", "OK");
    return;
}

var file = await CrossMedia.Current.TakePhotoAsync(new Plugin.Media.Abstractions.StoreCameraMediaOptions
{
    PhotoSize = Plugin.Media.Abstractions.PhotoSize.Medium,
    Directory = "Sample",
    Name = "test.jpg"
});

if (file == null)
    return;

await DisplayAlert("File Location", file.Path, "OK");