写一个判断蓝牙信号强度的demo

好的，以下是一个简单的Android BLE应用程序示例，可以扫描BLE设备并显示它们的信号强度：

1. 首先，在AndroidManifest.xml文件中添加以下权限：

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

2. 在您的布局文件中添加一个ListView，用于显示扫描到的设备列表：

<ListView
    android:id="@+id/device_list"
    android:layout_width="match_parent"
    android:layout_height="match_parent" />

3. 在您的活动中，实现BLE扫描回调函数并在回调函数中处理RSSI数据：

public class MainActivity extends AppCompatActivity {

    private BluetoothAdapter mBluetoothAdapter;
    private ListView mDeviceList;
    private DeviceListAdapter mAdapter;
    private List<BluetoothDevice> mDeviceArrayList = new ArrayList<>();

    private final ScanCallback mScanCallback = new ScanCallback() {
        @Override
        public void onScanResult(int callbackType, ScanResult result) {
            BluetoothDevice device = result.getDevice();
            int rssi = result.getRssi(); // 获取RSSI值
            mAdapter.addDevice(device, rssi); // 添加设备和RSSI值到列表中
        }
    };

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

        mDeviceList = findViewById(R.id.device_list);
        mAdapter = new DeviceListAdapter(this, mDeviceArrayList);
        mDeviceList.setAdapter(mAdapter);

        // 获取BluetoothAdapter
        final BluetoothManager bluetoothManager =
                (BluetoothManager) getSystemService(Context.BLUETOOTH_SERVICE);
        mBluetoothAdapter = bluetoothManager.getAdapter();
    }

    public void scanDevices(View view) {
        // 检查是否已启用蓝牙
        if (mBluetoothAdapter == null || !mBluetoothAdapter.isEnabled()) {
            Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
            startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);
            return;
        }

        // 扫描BLE设备
        mDeviceArrayList.clear();
        mAdapter.notifyDataSetChanged();

        ScanSettings settings = new ScanSettings.Builder()
                .setScanMode(ScanSettings.SCAN_MODE_LOW_LATENCY)
                .build();
        List<ScanFilter> filters = new ArrayList<>();
        mBluetoothAdapter.getBluetoothLeScanner().startScan(filters, settings, mScanCallback);
    }

    private class DeviceListAdapter extends BaseAdapter {
        private List<BluetoothDevice> mList;
        private LayoutInflater mInflater;

        public DeviceListAdapter(Context context, List<BluetoothDevice> deviceList) {
            mList = deviceList;
            mInflater = LayoutInflater.from(context);
        }

        public void addDevice(BluetoothDevice device, int rssi) {
            if (!mList.contains(device)) {
                mList.add(device);
            }
            notifyDataSetChanged();
        }

        @Override
        public int getCount() {
            return mList.size();
        }

        @Override
        public Object getItem(int position) {
            return mList.get(position);
        }

        @Override
        public long getItemId(int position) {
            return position;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {
            if (convertView == null) {
                convertView = mInflater.inflate(R.layout.list_item_device, parent, false);
            }
            BluetoothDevice device = mList.get(position);
            TextView nameTextView = convertView.findViewById(R.id.device_name);
            TextView addressTextView = convertView.findViewById(R.id.device_address);
            TextView rssiTextView = convertView.findViewById(R.id.device_rssi);
            nameTextView.setText(device.getName());
            addressTextView.setText(device.getAddress());
            rssiTextView.setText(String.valueOf(getItem(position)));
            return convertView;
        }
    }
}

4. 最后，在您的列表项布局文件中添加一个TextView，用于显示设备的RSSI值：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="?android:listPreferredItemHeight"
    android:orientation="vertical">

    <TextView
        android:id="@+id/device_name"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceListItemSmall"
        android:textStyle="bold"
        android:paddingLeft="16dp"/>

    <TextView
        android:id="@+id/device_address"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceListItemSmall"
        android:paddingLeft="16dp"/>

    <TextView
        android:id="@+id/device_rssi"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:textAppearance="?android:attr/textAppearanceListItemSmall"
        android:paddingLeft="16dp"/>
</LinearLayout>

这样，当您点击扫描按钮时，应用程序将开始扫描BLE设备，并将它们的名称，地址和RSSI值显示在列表中。希望这可以帮助您入门BLE编程。