Xamarin.Andorid 调用相机拍照

https://www.jianshu.com/p/29b349ff7f1a

第一步：XML布局文件

<?xml version="1.0" encoding="utf-8"?>
<androidx.coordinatorlayout.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <Button
        android:id="@+id/take_photo"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="调用摄像头拍照"
        android:textSize="20sp" />

    <ImageView
        android:id="@+id/picture"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:contentDescription="description"
        />

</androidx.coordinatorlayout.widget.CoordinatorLayout>

第二步：添加权限

<uses-permission android:name="android.permission.INTERNET" />
    <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
    <uses-permission android:name="android.permission.CAMERA" />
    <uses-permission android:name="android.permission.MANAGE_DOCUMENTS" />
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.READ_USER_DICTIONARY" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_USER_DICTIONARY" />

第三步：application添加内容提供者

说明：在<application></application>中，但不在<Activity></Activity>中

  <!-- 为调用相机拍照设置内容提供者 -->
      <provider
          android:name="androidx.core.content.FileProvider"
          android:authorities="com.example.mydemo.fileprovider"
          android:exported="false"
          android:grantUriPermissions="true">
          <meta-data
              android:name="android.support.FILE_PROVIDER_PATHS"
              android:resource="@xml/file_paths" />
      </provider>

第四步：为application添加属性值

<!--   android:requestLegacyExternalStorage="true"-->

<application android:allowBackup="true"
               android:icon="@mipmap/ic_launcher"
               android:label="@string/app_name"
               android:roundIcon="@mipmap/ic_launcher_round"
               android:supportsRtl="true"
               android:theme="@style/AppTheme"
               android:requestLegacyExternalStorage="true"
               >

      <!-- 为调用相机拍照设置内容提供者 -->
      <provider
          android:name="androidx.core.content.FileProvider"
          android:authorities="com.example.mydemo.fileprovider"
          android:exported="false"
          android:grantUriPermissions="true">
          <meta-data
              android:name="android.support.FILE_PROVIDER_PATHS"
              android:resource="@xml/file_paths" />
      </provider>

  </application>

第五步：在Resources中新建文件夹xml并创建file_paths.xml布局文件

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
    <external-path
        name="my_images"
        path="."/>
</paths>

第六步：activity实现

 [Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]
    public class MainActivity : AppCompatActivity
    {

        public const  int TAKE_PHOTO = 1;//声明一个请求码，用于识别返回的结果
        private ImageView picture;
        private Android.Net.Uri imageUri;
        private Button CaptureButton;
        private String filePath = Android.OS.Environment.ExternalStorageDirectory + File.Separator + "output_image.jpg";

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            Xamarin.Essentials.Platform.Init(this, savedInstanceState);
            SetContentView(Resource.Layout.activity_main);

            RequestPermissions(LuoPermission.LuoPermissionList, 0);
            CaptureButton = (Button)FindViewById(Resource.Id.take_photo);
            picture = (ImageView)FindViewById(Resource.Id.picture);

            CaptureButton.Click += (object sender, System.EventArgs e) =>
            {
                TakePhoto();
            };

            SetDefualtImage();

        }
        public override void OnRequestPermissionsResult(int requestCode, string[] permissions, [GeneratedEnum] Permission[] grantResults)
        {
            Xamarin.Essentials.Platform.OnRequestPermissionsResult(requestCode, permissions, grantResults);

            base.OnRequestPermissionsResult(requestCode, permissions, grantResults);
        }

        void TakePhoto()
        {
            requestPermission();

        }

        //动态请求权限
        private void requestPermission()
        {

            if (ContextCompat.CheckSelfPermission(this, Manifest.Permission.WriteExternalStorage) != Permission.Granted)
            {
                //请求权限
                ActivityCompat.RequestPermissions(this, new String[] { Manifest.Permission.WriteExternalStorage, Manifest.Permission.Camera }, 1);
            }
            else
            {
                //调用
                requestCamera();
            }
        }
        private void requestCamera()
        {
            File outputImage = new File(filePath);
            /*
            创建一个File文件对象，用于存放摄像头拍下的图片，我们把这个图片命名为output_image.jpg
            并把它存放在应用关联缓存目录下，调用getExternalCacheDir()可以得到这个目录，为什么要
            用关联缓存目录呢？由于android6.0开始，读写sd卡列为了危险权限，使用的时候必须要有权限，
            应用关联目录则可以跳过这一步
             */
            try//判断图片是否存在，存在则删除在创建，不存在则直接创建
            {
                if (!outputImage.ParentFile.Exists())
                {
                    outputImage.ParentFile.Mkdirs();
                }
                if (outputImage.Exists())
                {
                    outputImage.Delete();
                }

                outputImage.CreateNewFile();

                if (Build.VERSION.SdkInt >= (BuildVersionCodes)24)
                {
                    imageUri = FileProvider.GetUriForFile(this,
                            "com.example.mydemo.fileprovider", outputImage);
                }
                else
                {
                    imageUri = Android.Net.Uri.FromFile(outputImage);
                }

                //使用隐示的Intent，系统会找到与它对应的活动，即调用摄像头，并把它存储
                Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
                intent.PutExtra(MediaStore.ExtraOutput, imageUri);
                StartActivityForResult(intent, TAKE_PHOTO);
                //调用会返回结果的开启方式，返回成功的话，则把它显示出来

            }
            catch (IOException e)
            {
                e.PrintStackTrace();
            }

        }

        protected override void OnActivityResult(int requestCode, [GeneratedEnum] Result resultCode, Intent data)
        {
            base.OnActivityResult(requestCode, resultCode, data);
            switch (requestCode)
            {
                case TAKE_PHOTO:
                    if (resultCode ==  Result.Ok)
                    {
                        try
                        {

                            Bitmap bitmap = BitmapFactory.DecodeStream(ContentResolver.OpenInputStream(imageUri));
                            picture.SetImageBitmap(bitmap);
                            //将图片解析成Bitmap对象，并把它显现出来
                        }
                        catch (FileNotFoundException e)
                        {
                            e.PrintStackTrace();
                        }
                    }
                    break;
                default:
                    break;
            }
        }

        //处理返回结果的函数，下面是隐示Intent的返回结果的处理方式，具体见以前我所发的intent讲解
        public override void OnActivityReenter(int resultCode, Intent data)
        {
            base.OnActivityReenter(resultCode, data);

        }

        //设置保存拍照图片——>再次关闭app重新打开显示为上次拍照照片
        private void SetDefualtImage()
        {
            File outputImage = new File(filePath);
            if (!outputImage.Exists())
            {
                return;
            }
            picture.SetImageBitmap(BitmapFactory.DecodeFile(filePath));
        }

    }

Github 地址：https://github.com/LuoCoreTestDeom/Android-PaiZhao-Photograph
不能放在gitee ：因为这个东西太坑了，比github 还要坑，C坑C 是最狠的，比老美狠多了