写一个手机app 扫描连接蓝牙设备然后发送数据

好的，以下是一个Android手机App扫描连接蓝牙设备并发送数据的代码示例：

首先，我们需要添加蓝牙权限和依赖库到AndroidManifest.xml和build.gradle文件中。

<!-- AndroidManifest.xml -->
<uses-permission android:name="android.permission.BLUETOOTH" />
<uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />

<!-- build.gradle -->
dependencies {
    implementation 'com.android.support:appcompat-v7:28.0.0'
    implementation 'com.android.support:design:28.0.0'
    implementation 'com.android.support.constraint:constraint-layout:1.1.3'
    implementation 'com.android.support:support-v4:28.0.0'
    implementation 'com.android.support:cardview-v7:28.0.0'
    implementation 'com.android.support:recyclerview-v7:28.0.0'

    implementation 'io.reactivex.rxjava2:rxjava:2.2.10'
    implementation 'io.reactivex.rxjava2:rxandroid:2.1.1'
    implementation 'com.jakewharton.rxbinding2:rxbinding:2.2.0'
}

接下来，我们创建一个MainActivity，并添加蓝牙连接和数据发送的逻辑。

public class MainActivity extends AppCompatActivity {

    private static final int REQUEST_ENABLE_BT = 1;
    private BluetoothAdapter bluetoothAdapter;
    private BluetoothDevice device;
    private BluetoothSocket socket;
    private InputStream inputStream;
    private OutputStream outputStream;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        if (bluetoothAdapter == null) {
            Toast.makeText(this, "Device doesn't support Bluetooth", Toast.LENGTH_SHORT).show();
            finish();
        }

        if (!bluetoothAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
        }

        findViewById(R.id.btn_scan).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                scanDevices();
            }
        });

        findViewById(R.id.btn_send).setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                sendData();
            }
        });
    }

    private void scanDevices() {
        IntentFilter filter = new IntentFilter(BluetoothDevice.ACTION_FOUND);
        registerReceiver(receiver, filter);

        if (bluetoothAdapter.isDiscovering()) {
            bluetoothAdapter.cancelDiscovery();
        }
        bluetoothAdapter.startDiscovery();
    }

    private final BroadcastReceiver receiver = new BroadcastReceiver() {
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (BluetoothDevice.ACTION_FOUND.equals(action)) {
                BluetoothDevice device = intent.getParcelableExtra(BluetoothDevice.EXTRA_DEVICE);
                if (device.getName().equals("Bluetooth Device Name")) {
                    MainActivity.this.device = device;
                    bluetoothAdapter.cancelDiscovery();
                }
            }
        }
    };

    private void sendData() {
        if (device == null) {
            Toast.makeText(this, "No device connected", Toast.LENGTH_SHORT).show();
            return;
        }

        try {
            socket = device.createRfcommSocketToServiceRecord(UUID.fromString("00001101-0000-1000-8000-00805F9B34FB"));
            socket.connect();
            inputStream = socket.getInputStream();
            outputStream = socket.getOutputStream();

            String data = "Hello World";
            outputStream.write(data.getBytes());
            Toast.makeText(this, "Data sent successfully", Toast.LENGTH_SHORT).show();
        } catch (IOException e) {
            Toast.makeText(this, "Failed to send data", Toast.LENGTH_SHORT).show();
        }
    }

    @Override
    protected void onDestroy() {
        super.onDestroy();

        if (bluetoothAdapter != null) {
            bluetoothAdapter.cancelDiscovery();
        }

        try {
            if (socket != null) {
                socket.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

以上代码中，我们首先检查设备是否支持蓝牙，并启动蓝牙。

然后，我们添加了扫描设备和发送数据的逻辑。在扫描设备的过程中，我们注册了一个广播接收器来获取蓝牙设备列表。在发送数据的过程中，我们先创建一个蓝牙Socket连接，然后获取输入输出流，并将数据发送到设备中。

注意，需要替换代码中的“Bluetooth Device Name”和UUID为你自己的设备名称和UUID。

希望这个例子能够帮助你开始蓝牙开发。