MASA MAUI Plugin 安卓藍芽低功耗（一）藍芽掃描

專案背景

MAUI的出現，賦予了廣大Net開發者開發多平臺應用的能力，MAUI 是Xamarin.Forms演變而來，但是相比Xamarin效能更好，可擴充套件性更強，結構更簡單。但是MAUI對於平臺相關的實現並不完整。

所以MASA團隊開展了一個實驗性專案，意在對微軟MAUI的補充和擴充套件，專案地址 https://github.com/BlazorComponent/MASA.Blazor/tree/main/src/Masa.Blazor.Maui.Plugin

每個功能都有單獨的demo演示專案，考慮到app安裝檔案體積（雖然MAUI已經整合裁剪功能，但是該功能對於程式碼本身有影響），屆時每一個功能都會以單獨的nuget包的形式提供，方便 測試，現在專案才剛剛開始，但是相信很快就會有可以交付的內容啦。

前言

本系列文章面向移動開發小白，從零開始進行平臺相關功能開發，演示如何參考平臺的官方文件使用MAUI技術來開發相應功能。

介紹

如果你對BLE的相關概念不瞭解，可以參考 開發者官網連結 : 藍芽低功耗-安卓(https://developer.android.google.cn/guide/topics/connectivity/bluetooth-le/)

本文JAVA相關程式碼均來自安卓開發者官網

開發步驟

新建專案

在vs中新建一個基於 MAUI Blazor 的專案 MauiBlueToothDemo ，然後新增一個 MAUI類庫 專案 Masa.Maui.Plugin.Bluetooth

新增許可權

專案建立好了之後，我們首先介紹一下BLE需要的安卓許可權，相信大家對各種APP首次開啟的許可權確認彈窗應該不會陌生。

<!--藍芽許可權-->
	<uses-permission android:name="android.permission.BLUETOOTH" />
	<!--讓應用啟動裝置發現或操縱藍芽設定-->
	<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
	<!-- 如果設配Android9及更低版本，可以申請 ACCESS_COARSE_LOCATION -->
	<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />

private class BluetoothPermissions : Permissions.BasePlatformPermission
        {
            public override (string androidPermission, bool isRuntime)[] RequiredPermissions =>
                new List<(string androidPermission, bool isRuntime)>
                {
                    (global::Android.Manifest.Permission.AccessFineLocation, true),
                    (global::Android.Manifest.Permission.Bluetooth, true),
                    (global::Android.Manifest.Permission.BluetoothAdmin, true),
                }.ToArray();
        }

我們在MasaMauiBluetoothService類內部新增一個方法，來實現動態獲取許可權

publicasyncTask<bool>CheckAndRequestBluetoothPermission()
{
varstatus=awaitPermissions.CheckStatusAsync<BluetoothPermissions>();

if(status==PermissionStatus.Granted)
returntrue;
status=awaitPermissions.RequestAsync<BluetoothPermissions>();

if(status==PermissionStatus.Granted)
returntrue;
returnfalse;
}

設定BLE

JAVA 程式碼
private BluetoothAdapter bluetoothAdapter;
...
// Initializes Bluetooth adapter.
final BluetoothManager bluetoothManager =
        (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
bluetoothAdapter = bluetoothManager.getAdapter();

在編寫平臺相關程式碼時，安卓的系統管理服務都是同 getSystemService 方法獲取的，該方法的引數為系統服務的名稱，對應在MAUI中的方法為 Android.App.Application.Context.GetSystemService ，流程是完全一樣的，語法稍有不同，我們如法炮製，在 MasaMauiBluetoothService 中新增一個建構函式，和兩個欄位

private readonly BluetoothManager _bluetoothManager;
        private readonly BluetoothAdapter _bluetoothAdapter;
        public MasaMauiBluetoothService()
        {
            _bluetoothManager = (BluetoothManager)Android.App.Application.Context.GetSystemService(Android.App.Application.BluetoothService);
            _bluetoothAdapter = _bluetoothManager?.Adapter;
        }

public bool IsEnabled()
        {
            return _bluetoothAdapter is {IsEnabled: true};
        }

BLE掃描

與BLE裝置通訊，首先需要掃描出附近的BLE裝置，我們先看看Java怎麼實現的

JAVA 程式碼
/**
 * Activity for scanning and displaying available BLE devices.
 */
public class DeviceScanActivity extends ListActivity {

    private BluetoothAdapter bluetoothAdapter;
    private boolean mScanning;
    private Handler handler;

    // Stops scanning after 10 seconds.
    private static final long SCAN_PERIOD = 10000;
    ...
    private void scanLeDevice(final boolean enable) {
        if (enable) {
            // Stops scanning after a pre-defined scan period.
            handler.postDelayed(new Runnable() {
                @Override
                public void run() {
                    mScanning = false;
                    bluetoothAdapter.stopLeScan(leScanCallback);
                }
            }, SCAN_PERIOD);

            mScanning = true;
            bluetoothAdapter.startLeScan(leScanCallback);
        } else {
            mScanning = false;
            bluetoothAdapter.stopLeScan(leScanCallback);
        }
        ...
    }
...
}

JAVA 程式碼
private LeDeviceListAdapter leDeviceListAdapter;
...
// Device scan callback.
private BluetoothAdapter.LeScanCallback leScanCallback =
        new BluetoothAdapter.LeScanCallback() {
    @Override
    public void onLeScan(final BluetoothDevice device, int rssi,
            byte[] scanRecord) {
        runOnUiThread(new Runnable() {
           @Override
           public void run() {
               leDeviceListAdapter.addDevice(device);
               leDeviceListAdapter.notifyDataSetChanged();
           }
       });
   }
};

private class DevicesCallback : ScanCallback
        {
            private readonly EventWaitHandle _eventWaitHandle = new(false, EventResetMode.AutoReset);

            public List<BluetoothDevice> Devices { get; } = new();

            public void WaitOne()
            {
                Task.Run(async () =>
                {
                    await Task.Delay(5000);
                    _eventWaitHandle.Set();
                });

                _eventWaitHandle.WaitOne();
            }
            public override void OnScanResult(ScanCallbackType callbackType, ScanResult result)
            {
                System.Diagnostics.Debug.WriteLine("OnScanResult");

                if (!Devices.Contains(result.Device))
                {
                    Devices.Add(result.Device);
                }

                base.OnScanResult(callbackType, result);
            }
        }

private readonly ScanSettings _settings;
        private readonly DevicesCallback _callback;
        public MasaMauiBluetoothService()
        {
            _bluetoothManager = (BluetoothManager)Android.App.Application.Context.GetSystemService(Android.App.Application.BluetoothService);
            _bluetoothAdapter = _bluetoothManager?.Adapter;
               _settings = new ScanSettings.Builder()
                .SetScanMode(Android.Bluetooth.LE.ScanMode.Balanced)
                ?.Build();
            _callback = new DevicesCallback();
        }

這裡也很好理解， ScanSettings 通過 ScanSettings.Builder() 構造，用來配置藍芽的掃描模式，我們這裡使用平衡模式，具體式有如下三種：

ScanSettings.SCAN_MODE_LOW_POWER 低功耗模式(預設掃描模式,如果掃描應用程式不在前臺，則強制使用此模式。)

ScanSettings.SCAN_MODE_BALANCED 平衡模式

ScanSettings.SCAN_MODE_LOW_LATENCY 高功耗模式(建議僅在應用程式在前臺執行時才使用此模式。)

最後新增 ScanLeDeviceAsync 方法

public async Task<IReadOnlyCollection<BluetoothDevice>> ScanLeDeviceAsync()
        {
            //第一個引數可以設定過濾條件-藍芽名稱，名稱字首，服務號等,這裡暫時不設定過濾條件
            _bluetoothAdapter.BluetoothLeScanner.StartScan(null, _settings, _callback);
            await Task.Run(() =>
            {
                _callback.WaitOne();
            });
            _bluetoothAdapter.BluetoothLeScanner.StopScan(_callback);
            return _callback.Devices.AsReadOnly();
        }

StartScan 方法的第一個引數是過濾條件，可以根據名稱等進行過濾，我們暫不設定過濾。

測試

@page "/"
<MButton OnClick="ScanBLEDeviceAsync">掃描藍芽裝置</MButton>
<div class="text-center">
    <MDialog @bind-Value="ShowProgress" Width="500">
        <ChildContent>
            <MCard>
                <MCardTitle>
                    正在掃描藍芽裝置
                </MCardTitle>
                <MCardText>
                    <MProgressCircular Size="40" Indeterminate Color="primary"></MProgressCircular>
                </MCardText>
            </MCard>
        </ChildContent>
    </MDialog>
</div>

<MCard Class="mx-auto" MaxWidth="400" Tile>
    @foreach (var item in BluetoothDeviceList)
    {
        <MListItem>
            <MListItemContent>
                <MListItemTitle>@item</MListItemTitle>
            </MListItemContent>
        </MListItem>
    }
</MCard>

using Masa.Maui.Plugin.Bluetooth;
using Microsoft.AspNetCore.Components;

namespace MauiBlueToothDemo.Pages
{
    public partial class Index
    {
        private bool ShowProgress { get; set; }
        private List<string> BluetoothDeviceList { get; set; } = new();
        [Inject]
        private MasaMauiBluetoothService BluetoothService { get; set; }

        private async Task ScanBLEDeviceAsync()
        {
            if (BluetoothService.IsEnabled())
            {
                if (await BluetoothService.CheckAndRequestBluetoothPermission())
                {
                    ShowProgress = true;
                    var deviceList = await BluetoothService.ScanLeDeviceAsync();
                    BluetoothDeviceList = deviceList.Where(o => !string.IsNullOrEmpty(o.Name)).Select(o => o.Name).Distinct().ToList();
                    ShowProgress = false;
                }
            }
        }
    }
}

不要忘記在MauiProgram.cs注入寫好的MasaMauiBluetoothService

#if ANDROID
        builder.Services.AddSingleton<MasaMauiBluetoothService>();
#endif

我們真機執行一下看看效果

同時在vs的輸出中可以看到列印的日誌

本文到此結束，下一篇我們實現具體的BLE的通訊。

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