Android Low Energy Bluetooth Gatt Connection Tutorial: Implementing with Kotlin

            ACTION_DISCOVERY_STARTED -> When Discovery starts 

            ACTION_DISCOVERY_FINISHED -> When Discovery finishes

            BluetoothDevice.ACTION_FOUND -> When a Bluetooth device is found 

      </a>
    </li>

    <li>
      <a href="javascript:void(0)">When connecting to a Bluetooth device

      It cannot be in startDiscovery

      You need to call cancelDiscovery() to end the discovery

      </a>
    </li>

    <li>
      <a href="javascript:void(0)">
      Discovery is not managed by the Activity

      But by the system service

      So, to be safe, you must use cancelDiscovery()

      To ensure Discovery is not running

      To avoid the device still being in Discovery

      when connecting to a Bluetooth device

      </a>
    </li>
    <li>
      <a href="javascript:void(0)">Discovery can only find currently discoverable Bluetooth devices
      </a>
    </li>

<li>
  <a href="javascript:void(0)">Observe if ACTION_STATE_CHANGED is STATE_ON
        If the current Bluetooth state is not STATE_ON, the API will return false

        Used to determine if the current state is one where updated values can be obtained

        <img src="/images/bluetooth/android_state.png" alt="Cover" class="w-full prose-img">
  </a>
</li>

<li>
  <a href="javascript:void(0)">If the target version used is less than or equal to Build.VERSION_CODES#R

        You need to request the Manifest.permission#BLUETOOTH_ADMIN permission from the user

        <img src="/images/bluetooth/android_R.png" alt="Cover" class="w-full prose-img" >
  </a>
</li>

<li>
  <a href="javascript:void(0)">
    If the target version used is greater than or equal to Build.VERSION_CODES#S

    You need to request the Manifest.permission#BLUETOOTH_SCAN permission from the user

    <img src="/images/bluetooth/android_S.png" alt="Cover" class="w-full prose-img" >
  </a>
</li>

<li>
  <a href="javascript:void(0)">Additionally

  You can request the Manifest.permission#ACCESS_FINE_LOCATION permission

  To increase the types of interactive Bluetooth devices

  Of course, you can also add the usesPermissionFlags="neverForLocation" tag in <b>uses-permission</b>

  To avoid requesting location permissions

  But the types of devices that can be searched will be limited

  </a>
</li>
</ol>
</div>

<div class="c-border-content-title-4">fun startScan ( callback:ScanCallback )</div>
<div class="table_container">
  <ol class="rectangle-list">
      <li><a href="javascript:void(0)">Start Bluetooth LE scan, scan results will be returned via callback</a></li>
      <li><a href="javascript:void(0)">Because this does not include filters,

      The default power-saving mode will stopScan when the screen is off,

      And resume when the screen is turned back on</a></li>
      <li><a href="javascript:void(0)">If the target version used is greater than or equal to Build.VERSION_CODES#Q,

      You need to request the Manifest.permission#ACCESS_FINE_LOCATION permission from the user</a></li>
      <li>
      <a href="javascript:void(0)">If the target version used is less than or equal to Build.VERSION_CODES#R,

      You need to request the Manifest.permission#BLUETOOTH_ADMIN permission from the user
        <img src="/images/bluetooth/android_R.png" alt="Cover" class="w-full prose-img">
      </a>
      </li>
      <li><a href="javascript:void(0)">If the target version used is greater than or equal to Build.VERSION_CODES#S,

      You need to request the Manifest.permission#BLUETOOTH_SCAN permission from the user
      <img src="/images/bluetooth/android_S.png" alt="Cover" class="w-full prose-img">
      </a>

      </li>
      <li><a href="javascript:void(0)">Additionally, you can request the Manifest.permission#ACCESS_FINE_LOCATION permission,

      to increase the types of interactive Bluetooth devices,

      of course, you can also add the usesPermissionFlags="neverForLocation" tag in &lt;uses-permission&gt;,

      to avoid requesting location permissions,

      but the types of devices that can be discovered will be limited</a></li>
  </ol>
</div>

<div class="c-border-content-title-4">fun startScan(filters:List&lt;ScanFilter&gt;,settings:ScanSettings,callback:ScanCallback)</div>
<div class="table_container">
  <ol class="rectangle-list">
      <li>
        <a href="javascript:void(0)">Features include the six items from the above startScan ( callback:ScanCallback )
        </a>
      </li>
      <li>
        <a href="https://developer.android.com/reference/android/bluetooth/le/ScanFilter" target="_blank" rel="noopener noreferrer">
        Use ScanFilter to filter the scan results,

        mainly supporting the following items,

          <img src="/images/bluetooth/android_filter.png" alt="bluetooth android filter" style="width: 80%" class="prose-img">
        </a>
      </li>
      <li><a href="https://developer.android.com/reference/android/bluetooth/le/ScanSettings#summary" target="_blank" rel="noopener noreferrer">
      Also use ScanSettings to set how to handle the returned callback,

      such as: return each successfully filtered data, only return the first successfully filtered data... etc.</a></li>
  </ol>
</div>

## Actual Development: How to Perform Bluetooth Scanning

Add the required permissions mentioned above in the manifest

<script src="https://gist.github.com/waitzShigoto/fc855c0ab9c4667df49b253595744d08.js"></script>

<div class="c-border-content-title-4">Request Permissions in the Code</div>
Below is an extension

that can be used universally

```kotlin
  requestMultiplePermissions(Manifest.permission.ACCESS_FINE_LOCATION,...

private val bluetoothAdapter: BluetoothAdapter? = BluetoothAdapter.getDefaultAdapter()

Register to listen for BluetoothDevice.ACTION_FOUND

val filter = IntentFilter(BluetoothDevice.ACTION_FOUND)
    requireContext().registerReceiver(receiver, filter)

Extend a BroadcastReceiver

and use the receiver type to return the result bleDevice

private val receiver = DeviceListBoardCast { bleDevice ->

        deviceViewModel.addDevice(bleDevice)
    }

其中取資料的方式是，到時候掃描出來的資料可以從這幾個拿

val device: BluetoothDevice = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE)!!
val rssi = intent.getShortExtra(BluetoothDevice.EXTRA_RSSI, Short.MIN_VALUE).toInt()
val uuidExtra = intent.getParcelableArrayExtra(BluetoothDevice.EXTRA_UUID)

繼承的BroadcastReceiver實作

前面已經拿到bluetoothAdapter跟註冊廣播監聽了

所以開始分別可以用startDiscovery、cancelDiscovery 來開始或結束掃描

bluetoothAdapter.startDiscovery()
bluetoothAdapter.cancelDiscovery()

這個函式

主要是進行掃描的開關

並搭配viewmodel與coroutine

做到用viewmodel紀錄刷新狀態，並透過coroutine掃描指定秒數 x 秒

如果不需要用到那麼複雜的話

直接用startDiscovery、cancelDiscovery去開發就行了

掃描的結果會返回剛剛DeviceListBoardCast {}內，

這邊根據自己專案去調整就行

我是用viewmodel來觀察資料

private val receiver = DeviceListBoardCast { bleDevice ->

        deviceViewModel.addDevice(bleDevice)
    }

實際開發：如何進行藍芽連線

這邊使用service的方式去串接

首先建立一個service

並建立Binder

用來onBind時返回實例給fragment去調用

在該service內創建一個 initialize()函式

用在之後bindservice時可以調用初始化

接著寫個gattCallback實例

這邊主要是onConnectionStateChange、onServicesDiscovered、onCharacteristicRead

分別是當有新的連接狀態改變、新的服務被發現、新的東西讀到後

返回的callback

這邊主要可以根據你的需求

去做判斷

gattCallback example:

The main part is to connect using the following two lines

val device = bluetoothAdapter!!.getRemoteDevice(address)

and

bluetoothGatt = device.connectGatt(this, false, gattCallback)

Pass the address you want to connect to

Get the BluetoothDevice you want to connect to

Then use the connectGatt method in the device to bind the Gatt device

Of course, you also need to pass in the gattCallback written earlier

The previous part is just a series of null checks

To ensure the app does not crash due to null

In the instantiation of gattCallback,

you will find a method named broadcastUpdate.

This method is mainly used to send broadcast messages,

you can define what to do in different situations according to your needs,

or what broadcast messages to return.

Simple connection and device search

That's about it

Next, the most important thing in Bluetooth is communication between terminals

So if you want to send and receive data

You need to find the service and characteristic

Here is a diagram

So we find it through the following method:

Bring in the gatt service obtained through the broadcast earlier

Then you can traverse to get the characteristic

Since the official Android has already wrapped the characteristic class for you

To read, you just need to call the relevant function:

And it will return to you in the previously defined BluetoothGattCallback

onCharacteristicRead

You just need to define the broadcast reception to get the data

Additionally, there is also a notify method in Bluetooth:

Similarly, it returns the result

In BluetoothGattCallback

Check onCharacteristicChanged

If you want to see how to capture Bluetooth packets through third-party tools

You can refer to: