有没有人能给出一个简短的、独立的例子来说明如何使用 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会很棒！
我已经尝试使用 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）。在网上找到的大多数代码片段（包括stackoverflow）都是不完整的，例如没有显示IMediaPicker 对象的实现或在哪里锚定拍照方法。
我终于为 iOS 和 Android 创建了一个最低限度的解决方案。
首先，让我们看看共享代码。App为了在共享类和特定于平台的代码之间轻松交互，我们将静态存储Instance在public static App：
public static App Instance;
此外，我们将显示一个Image，稍后将填充内容。所以我们创建一个成员：
readonly Image image = new Image();
在App构造函数中，我们存储Instance并创建页面内容，这是一个简单button的前面提到的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将在稍后分配给它。
public event Action ShouldTakePicture = () => {};
最后，我们提供了一个公共方法来显示捕获的图像：
public void ShowImage(string filepath)
{
image.Source = ImageSource.FromFile(filepath);
}
在 Android 上，我们修改MainActivity. 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");
最后，我们可以使用createdOnCreate的 static并分配一个匿名事件处理程序，它将启动一个新的用于捕获图像：InstanceAppIntent
App.Instance.ShouldTakePicture += () => {
var intent = new Intent(MediaStore.ActionImageCapture);
intent.PutExtra(MediaStore.ExtraOutput, Uri.FromFile(file));
StartActivityForResult(intent, 0);
};
最后但同样重要的是，我们的活动必须对生成的图像做出反应。它只会将其文件路径推送到共享ShowImage方法。
protected override void OnActivityResult(int requestCode, Result resultCode, Intent data)
{
base.OnActivityResult(requestCode, resultCode, data);
App.Instance.ShowImage(file.Path);
}
就是这样！只是不要忘记在“AndroidManifest.xml”中设置“Camera”和“WriteExternalStorage”权限！
对于 iOS 实现，我们创建了一个自定义渲染器。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
{
...
}
我们重写该ViewDidAppear方法并添加以下部分。
创建一个引用相机的新图像选择器控制器：
var imagePicker = new UIImagePickerController { SourceType = UIImagePickerControllerSourceType.Camera };
一旦ShouldTakePicture引发事件，就呈现图像选择器控制器：
App.Instance.ShouldTakePicture += () => PresentViewController(imagePicker, true, null);
拍照后保存到MyDocuments文件夹，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，我们需要处理取消图像拍摄过程：
imagePicker.Canceled += (sender, e) => DismissViewController(true, null);
试试 James Montemagno 的MediaPlugin。
您可以使用Package Manager Console安装插件，只需键入并运行Install-Package Xam.Plugin.Media -Version 2.6.2，或者转到Manage NuGet Packages...并键入Xam.Plugin.Media并安装插件。（插件必须安装在您的所有项目中 - 包括客户端项目）
将提示readme.txt并按照那里的说明进行操作。之后，将以下代码（根据需要）添加到您的共享项目中。上述readme.txt文件中要遵循的说明如下。
在您的 BaseActivity 或 MainActivity（对于 Xamarin.Forms）中添加以下代码：
public override void OnRequestPermissionsResult(int requestCode, string[] permissions, Permission[] grantResults)
{
PermissionsImplementation.Current.OnRequestPermissionsResult(requestCode, permissions, grantResults);
}
您还必须添加一些额外的配置文件以遵守新的严格模式：
将以下内容添加到 < application > 标签内的 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 必须设置为您的应用程序包名称！
在 Resources 文件夹中添加一个名为 xml 的新文件夹，并添加一个名为file_paths.xml
添加以下代码：
<?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 必须设置为您的应用程序包名称！
为了访问设备的相机和照片/视频库，NSCameraUsageDescription您的应用程序需要在 Info.plist 中有密钥。NSPhotoLibraryUsageDescription如果您使用库的视频功能，那么您还必须添加NSMicrophoneUsageDescription. 当系统提示用户提供访问这些设备功能的权限时，您为每个密钥提供的字符串将显示给用户。
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>
要简单地打开相机，保存照片并显示带有文件路径的警报，请在共享项目中输入以下内容。
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");
这是在 Xamarin Forms 跨 Xamarin iOS 上的操作方法。
这是一个很好的开始，但它需要首先呈现一个页面，您可以在其中指定 UIApplication 为它提供用于相机/照片选择器控制器的 UIView。
https://stackoverflow.com/a/28299259/1941942
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;
}
}
这是在我的应用程序中运行异步相机捕获所需的：
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;
}
如果您需要授权例程，请确保您也填写了相机用途info.plist，这是获得授权的功能：
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;
}
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;
}
}