安卓系統android使用C# .NET Xamarin框架呼叫相機拍照

引言

Xamarin始創于2011年，旨在使移動開發變得難以置信地迅捷和簡單，Xamarin的產品簡化了針對多種平臺的應用開發，包括iOS、Android、Universal Windows Platform、Watch OS、tvOS和Mac App，Xamarin由許多著名的開源社區開發者創立和參與，而且也是Mono專案的主導者——C#與·NET框架的開源、跨平臺實作，（摘自“百度百科”）
本文參考Ufinix的視頻教程 “ Xamarin Android Tutorials - Capture Image from Camera ”完成，

一、用到的軟體、包

1.1 VS2019 community 安裝.Net桌面開和使用.Net移動開發；
2.2 安裝這兩個勾選項后，我這里的組件有.NET Framework4.7.2和Android SDK API 28，
1.3 安裝安卓模擬器，勾選“使用c++進行移動開發”，在應用詳情里找到Google Android Emulator和Intel硬體加速HAXM兩個組件，用來創建安卓模擬器使用，

二、創建Android應用（Xamarin），

安裝完，按圖中模板創建新專案，當然，第一項Xamarin.Forms肯定也是可以的，它是有點像asp.netcore的MVC架構，即模型，視圖，控制器分離，業務邏輯更清晰；

三、增加Nuget中庫Xam.Plugin.Media的參考

四、參考參考包Xam.Plugin.Media的readme檔案操作；

Android
This library uses Xamarin.Essentials for permissions and other funcationality. Please ensure that you have sset it up correctly:
https://docs.microsoft.com/xamarin/essentials/get-started

protected override void OnCreate(Bundle savedInstanceState) {
    //...
    base.OnCreate(savedInstanceState);
    Xamarin.Essentials.Platform.Init(this, savedInstanceState); // add this line to your code, it may also be called: bundle
    //...

And for permissions:

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

NB: The WRITE_EXTERNAL_STORAGE, READ_EXTERNAL_STORAGE permissions are required, but the library will automatically add this for you. Additionally, if your users are running Marshmallow the Plugin will automatically prompt them for runtime permissions. The following has also been added for you: [assembly: UsesFeature(“android.hardware.camera”, Required = false)] [assembly: UsesFeature(“android.hardware.camera.autofocus”, Required = false)] You must also add a few additional configuration files to adhere to the new strict mode:
a1. Add the following to your AndroidManifest.xml inside the tags:

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

a2. Add a new folder called xml into your Resources folder
a3. Add a new XML file called file_paths.xml and add the following code:

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

You can read more at: https://developer.android.com/training/camera/photobasics.html
Android:
This plugin uses the Xamarin.Essentials, please follow the setup guide.
Xamarin.Essentials.Platform.Init(this, bundle);

五、搭建Andoid的程式界面和程式邏輯，

5.1 在Resources>layout>activity_main.xml檔案/頁面中增加一個Button按鈕“CaptureButton”和ImageView控制元件“imageView1”：

 <ImageView
        android:contentDescription="@string/Photo1"
        android:src="@android:drawable/ic_menu_gallery"
        android:layout_width="match_parent"
        android:layout_height="337.5dp"
        android:id="@+id/imageView1" />
    <SeekBar
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/seekBar1" />
    <Button
        android:text="@string/Capture"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/CaptureButton" />

5.2 在MainActivity.cs中寫按鈕函式，這里附上該檔案的全部原始碼以供大家參考:

using System;
using Android;
using Android.App;
using Android.Graphics;
using Android.OS;
using Android.Runtime;
using Android.Support.Design.Widget;
using Android.Support.V7.App;
using Android.Views;
using Android.Widget;
using Plugin.Media;

namespace XamarinCamera
{
    [Activity(Label = "@string/app_name", Theme = "@style/AppTheme.NoActionBar", MainLauncher = true)]
    public class MainActivity : AppCompatActivity
    {
        ImageView ImgView1;
        Button CaptureButton;
        readonly string[] permissionGroup =
        {
            Manifest.Permission.ReadExternalStorage,
            Manifest.Permission.WriteExternalStorage,
            Manifest.Permission.Camera
        };
        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);

            Xamarin.Essentials.Platform.Init(this, savedInstanceState);
            SetContentView(Resource.Layout.activity_main);

            RequestPermissions(permissionGroup, 0);

            CaptureButton = (Button)FindViewById(Resource.Id.CaptureButton);
            ImgView1 = (ImageView)FindViewById(Resource.Id.imageView1);
            CaptureButton.Click += (object sender, System.EventArgs e) =>
              {
                  TakePhoto();
              };

            Android.Support.V7.Widget.Toolbar toolbar = FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
            SetSupportActionBar(toolbar);

            FloatingActionButton fab = FindViewById<FloatingActionButton>(Resource.Id.fab);
            fab.Click += FabOnClick;
        }
        async void TakePhoto()
        {
            await CrossMedia.Current.Initialize();
            var file = await CrossMedia.Current.TakePhotoAsync(new Plugin.Media.Abstractions.StoreCameraMediaOptions
            {
                PhotoSize=Plugin.Media.Abstractions.PhotoSize.Medium,
                CompressionQuality=40,
                Name="myImage.jpg",
                Directory="sample"
            });
            if (file == null)
            {
                return;
            }
            byte[] imageArray = System.IO.File.ReadAllBytes(file.Path);
            Bitmap bitmap = BitmapFactory.DecodeByteArray(imageArray, 0, imageArray.Length);
            ImgView1.SetImageBitmap(bitmap);

        }

        public override bool OnCreateOptionsMenu(IMenu menu)
        {
            MenuInflater.Inflate(Resource.Menu.menu_main, menu);
            return true;
        }

        public override bool OnOptionsItemSelected(IMenuItem item)
        {
            int id = item.ItemId;
            if (id == Resource.Id.action_settings)
            {
                return true;
            }

            return base.OnOptionsItemSelected(item);
        }

        private void FabOnClick(object sender, EventArgs eventArgs)
        {
            View view = (View) sender;
            Snackbar.Make(view, "Replace with your own action", Snackbar.LengthLong)
                .SetAction("Action", (Android.Views.View.IOnClickListener)null).Show();
        }

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

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

六、運行驗證效果