Xamarin.Form 蓝牙ble

　　本文介绍Xamarin.Form的蓝牙使用方法，开始之前说说题外话，就Xamarin.Form来说，在国内是没多少人在弄的，但对于我自己来说，是吃了这碗饭，也希望在这行做的人越来越多，越来越好，本人2016年开始入使用Xamarin.Form开发App，那时候刚微软刚收购Xamarin，也正式开源免费给开发者使用，但那时候的本说实话是有多不完善的，直到现在微软依然有很多不完善的功能，所以在国内学这个，一般是由公司高层推这个技术，直接至底向上的非常少。微软的东西在国内环境来说，多不太好，很多大的互联网公司都比较少用，但是我要强调的是，Xamarin.Form本身其实并不太适合做界面变化太多，变化太大的东西，如果你的项目需要优秀的界面，炫酷的特效，那原生是比较好的选择，而这个特性是互联网公司的特性，所以互联网公司不太适合使用Xamarin.Form。Xamarin适合界面少，但是业务比较复杂的项目，如IOT项目。也比较适合传统企业而不是互联网公司。所以在前面一篇文章中，我介绍了MQTT协议，现在介绍底功耗蓝牙协议。

　　这里使用ble.net库，直接使用nuget查找相应的包就可以了，ble.net库是一个混合平台的低功耗蓝牙库，可用于开发Android、iOS、UWP平台的BLE客户端。支持的平台和版本如下

Platform	Version
Xamarin.iOS	iOS 8.3+
Xamarin.Android	API 18+
Windows 10(UWP)	1709+

　　在引用包的时候注意：在Xamarin.Form层引用ble.net包，在xamarin.Android层引用ble.net 和ble.net-android包，在Xamarin.Form层引用ble.net和ble.net-ios包。

　　Android 平台

　　添加权限，在Android 6.0或更高版本中需要获取危险的位置权限，所以在AndroidManifesst.xml文件中添加

<uses-permission android:name="android.permission.BLUETOOTH" />
    <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
    <uses-permission android:name="android.permission.BLUETOOTH_PRIVILEGED" />
  <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
  <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" />
  <uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />

　　初始化BluetoothLowEnergyAdapter(只有Android平台需要，iOS和UWP平台不需要)。如果你想让IBluetoothLowEnergyAdapter.DisableAdapter() 和 IBluetoothLowEnergyAdapter.EnableAdapter()起作用，你需要在你的Main Activity中添加：

protected override void OnCreate( Bundle bundle )
{
   // ...
   BluetoothLowEnergyAdapter.Init( this );
   // ...
}

　　如果你要IBluetoothLowEnergyAdapter.CurrentState.Subscribe()方法起作用，你还需要在Activity中添加：

protected sealed override void OnActivityResult( Int32 requestCode, Result resultCode, Intent data )
{
   BluetoothLowEnergyAdapter.OnActivityResult( requestCode, resultCode, data );
}

　　iOS 平台

　　必须添加使用蓝牙的提示，并且苹果公司上架App会审核，需正确填写Info.plist文件

<key>UIBackgroundModes</key>
<array>
   <string>bluetooth-central</string>
</array>
<key>NSBluetoothPeripheralUsageDescription</key>
<string>[MyAppNameHere] would like to use bluetooth.</string>

　　所有平台都需要初始化一个

IBluetoothLowEnergyAdapter ble =
BluetoothLowEnergyAdapter.ObtainDefaultAdapter()

同时传到Xamarin.Form层。

　　App内开启蓝牙：使用如下方法检查和启用手机蓝牙适配器

if(ble.AdapterCanBeEnabled && ble.CurrentState.IsDisabledOrDisabling()) {
   await ble.EnableAdapter();
}

　　开始扫描附近的蓝牙设备，可以扫描到各种设备，注意：超时时间不宜设置过长，通过测试，蓝牙设备不能一直扫描，需停一会在扫描一会这样使用。扫描能扫描出附近的蓝牙设备和特性。

var cts = new CancellationTokenSource(TimeSpan.FromSeconds( 30 ));
await ble.ScanForBroadcasts(
   // providing ScanSettings is optional
   new ScanSettings()
   {
      // Setting the scan mode is currently only applicable to Android and has no effect on other platforms.
      // If not provided, defaults to ScanMode.Balanced
      Mode = ScanMode.LowPower,

      // Optional scan filter to ensure that the observer will only receive peripherals
      // that pass the filter. If you want to scan for everything around, omit the filter.
      Filter = new ScanFilter()
      {
         AdvertisedDeviceName = "foobar",
         AdvertisedManufacturerCompanyId = 76,
         // peripherals must advertise at-least-one of any GUIDs in this list
         AdvertisedServiceIsInList = new List<Guid>(){ someGuid },
      },

      // ignore repeated advertisements from the same device during this scan
      IgnoreRepeatBroadcasts = false
   },
   // Your IObserver<IBlePeripheral> or Action<IBlePeripheral> will be triggered for each discovered
   // peripheral based on the provided scan settings and filter (if any).
   ( IBlePeripheral peripheral ) =>
   {
      // read the advertising data
      var adv = peripheral.Advertisement;
      Debug.WriteLine( adv.DeviceName );
      Debug.WriteLine( adv.Services.Select( x => x.ToString() ).Join( "," ) );
      Debug.WriteLine( adv.ManufacturerSpecificData.FirstOrDefault().CompanyName() );
      Debug.WriteLine( adv.ServiceData );

      // if we found what we needed, stop the scan manually
      cts.Cancel();

      // perhaps connect to the device (see next example)...
   },
   // Provide a CancellationToken to stop the scan, or use the overload that takes a TimeSpan.
   // If you omit this argument, the scan will timeout after BluetoothLowEnergyUtils.DefaultScanTimeout
   cts.Token
);

// scanning has stopped when code reached this point since the scan was awaited

　　如果你要连接蓝牙设备，采用如下方法：

var connection = await ble.ConnectToDevice(
   // The IBlePeripheral to connect to
   peripheral,
   // TimeSpan or CancellationToken to stop the
   // connection attempt.
   // If you omit this argument, it will use
   // BluetoothLowEnergyUtils.DefaultConnectionTimeout
   TimeSpan.FromSeconds( 15 ),
   // Optional IProgress<ConnectionProgress>
   progress => Debug.WriteLine(progress)
);

if(connection.IsSuccessful())
{
   var gattServer = connection.GattServer;
   // ... do things with gattServer here... (see later examples...)
}
else
{
   // Do something to inform user or otherwise handle unsuccessful connection.
   Debug.WriteLine( "Error connecting to device. result={0:g}", connection.ConnectionResult );
   // e.g., "Error connecting to device. result=ConnectionAttemptCancelled"
}

　　断开蓝牙方法：

await gattServer.Disconnect();

　　下列方法用来连接指定的蓝牙设备：

var connection = await ble.FindAndConnectToDevice(
   new ScanFilter()
      .SetAdvertisedDeviceName( "foo" )
      .SetAdvertisedManufacturerCompanyId( 0xffff )
      .AddAdvertisedService( guid ),
   TimeSpan.FromSeconds( 30 ) );
if(connection.IsSuccessful())
{
   // ...
}

　　调用蓝牙的读特性

try
{
   var value = await gattServer.ReadCharacteristicValue( someServiceGuid, someCharacteristicGuid );
}
catch(GattException ex)
{
   Debug.WriteLine( ex.ToString() );
}

　　监听通知特性

IDisposable notifyHandler;

try
{
   // Will also stop listening when gattServer
   // is disconnected, so if that is acceptable,
   // you don't need to store this disposable.
   notifyHandler = gattServer.NotifyCharacteristicValue(
      someServiceGuid,
      someCharacteristicGuid,
      // IObserver<Tuple<Guid, Byte[]>> or IObserver<Byte[]> or
      // Action<Tuple<Guid, Byte[]>> or Action<Byte[]>
      bytes => {/* do something with notification bytes */} );
}
catch(GattException ex)
{
   Debug.WriteLine( ex.ToString() );
}

// ... later, once done listening for notifications ...
notifyHandler.Dispose();

　　调用写特性，注意：在写的时候不能一直不停的调用这个方法，不然会发送不了，需要停顿500毫秒左右在发送第二个包。这点非常重要。

try
{
   // The resulting value of the characteristic is returned. In nearly all cases this
   // will be the same value that was provided to the write call (e.g. `byte[]{ 1, 2, 3 }`)
   var value = await gattServer.WriteCharacteristicValue(
      someServiceGuid,
      someCharacteristicGuid,
      new byte[]{ 1, 2, 3 } );
}
catch(GattException ex)
{
   Debug.WriteLine( ex.ToString() );
}

　　蓝牙有很多应用，需要自己多尝试，对于蓝牙的升级DFU功能，需要的可以找我。