使用Xamarin.Forms訪問攝像頭

Question

是否有人能夠提供一個關於如何使用Xamarin.Forms 1.3.x訪問相機的簡短，自包含的示例？ 只需調用本機相機應用程序並檢索生成的圖片就會很棒。 在Xamarin.Forms頁面上顯示實時視圖真棒！

我已經嘗試過使用Xamarin.Mobile和Xamarin.Forms.Labs，但我無法在兩個平台上使用任何解決方案（現在專注於Android和iOS）。 Web上發現的大多數代碼片段（包括stackoverflow）都是不完整的，例如沒有顯示IMediaPicker對象的實現或者錨定拍照方法的位置。

Answer 1

我終於為iOS和Android創建了最低限度的解決方案。

共享項目

首先，讓我們看一下共享代碼。 為了在共享App類和特定於平台的代碼之間輕松交互，我們在public static App存儲了一個靜態Instance ：

public static App Instance;

此外，我們將顯示一個Image ，稍后將填充內容。 所以我們創建一個成員：

readonly Image image = new Image();

在App構造函數中，我們存儲Instance並創建頁面內容，這是一個簡單的button和上述image ：

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,
           },
       },
   };
}

按鈕的單擊處理程序調用事件ShouldTakePicture 。 它是一個公共成員，特​​定於平台的代碼部分稍后將分配給它。

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

最后，我們提供了一種顯示捕獲圖像的公共方法：

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

Android項目

在Android上，我們修改了MainActivity 。 首先，我們為捕獲的圖像文件定義路徑：

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

在OnCreate結束時，我們可以使用創建的App的靜態Instance並分配一個匿名事件處理程序，它將啟動一個新的Intent來捕獲圖像：

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

最后但同樣重要的是，我們的活動必須對生成的圖像做出反應。 它只是將其文件路徑推送到共享的ShowImage方法。

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

就是這樣！ 只是不要忘記在“AndroidManifest.xml”中設置“Camera”和“WriteExternalStorage”權限！

iOS項目

對於iOS實現，我們創建了一個自定義渲染器。 因此，我們添加一個新文件“CustomContentPageRenderer”並在using語句后面添加相應的程序集屬性：

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

CustomContentPageRenderer繼承自PageRenderer ：

public class CustomContentPageRenderer: PageRenderer
{
    ...
}

我們覆蓋ViewDidAppear方法並添加以下部分。

創建一個新的圖像選擇器控制器參考相機：

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

一旦引發ShouldTakePicture事件，就呈現圖像選擇器控制器：

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

拍攝照片后，將其保存到MyDocuments文件夾並調用共享的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，我們需要處理取消圖像處理過程：

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

Answer 2

試試James Montemagno的MediaPlugin 。

您可以使用Package Manager Console安裝插件，只需鍵入並運行Install-Package Xam.Plugin.Media -Version 2.6.2或者轉到Manage NuGet Packages ...並鍵入Xam.Plugin.Media並安裝插件。 （必須在所有項目中安裝插件 - 包括客戶端項目）

將提示readme.txt並按照其中的說明進行操作。 之后， 將以下代碼 （根據需要）添加到共享項目中。 上述readme.txt文件中要遵循的說明如下。

對於Android Project

在您的BaseActivity或MainActivity（對於Xamarin.Forms）中添加以下代碼：

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

您還必須添加一些其他配置文件以遵守新的嚴格模式：

1. 將以下內容添加到< application >標記內的AndroidManifest.xml中：

    <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> 

   YOUR_APP_PACKAGE_NAME必須設置為您的應用包名稱！

2. 將名為xml的新文件夾添加到Resources文件夾中，並添加一個名為file_paths.xml的新XML文件

   添加以下代碼：

    <?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> 

   YOUR_APP_PACKAGE_NAME必須設置為您的應用包名稱！

對於iOS項目

您的應用程序需要在Info.plist中為NSCameraUsageDescription和NSPhotoLibraryUsageDescription提供密鑰才能訪問設備的攝像頭和照片/視頻庫。 如果您正在使用庫的視頻功能，則還必須添加NSMicrophoneUsageDescription 。 當提示用戶提供訪問這些設備功能的權限時，將為用戶顯示為每個密鑰提供的字符串。

如：

<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>

對於共享項目

要簡單地打開相機，保存照片並顯示帶有文件路徑的警報，請在共享項目中輸入以下內容。

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"); 

Answer 3

以下是如何在Xamarin Forms跨Xamarin iOS上完成的。

這是一個很好的基礎，但它需要首先渲染一個Page，你可以在其中為它指定UIApplication，以便為Camera / Photo Picker控制器提供UIView。

https://stackoverflow.com/a/28299259/1941942

便攜式項目

public interface ICameraProvider
{
    Task<CameraResult> TakePhotoAsync();
    Task<CameraResult> PickPhotoAsync();
}

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

iOS項目

[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;
    }
}

Answer 4

這是我需要在我的應用程序中運行異步攝像頭捕獲所需的：

在iOS中：

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;
}

如果您需要授權例程，請確保您也在info.plist填寫相機使用，這里是獲得授權的功能：

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;
}

---

在Android中：

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;
    }
}