安卓原生车机蓝牙自动回连代码

安卓原生车机的蓝牙自动回连功能通常涉及在车辆启动时检测到已配对的蓝牙设备，并自动连接。这涉及到系统的广播接收器以及与BluetoothAdapter交互。以下是一个简化的示例代码片段：

import android.bluetooth.BluetoothAdapter;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.IntentFilter;

public class BluetoothAutoConnect {
    private static final String ACTION_BLUETOOTH_STATE_CHANGED = "android.bluetooth.adapter.action.STATE_CHANGED";
    
    private BluetoothAdapter bluetoothAdapter;

    public BluetoothAutoConnect(Context context) {
        this.bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
        
        // Register a BroadcastReceiver to listen for state changes
        IntentFilter intentFilter = new IntentFilter();
        intentFilter.addAction(ACTION_BLUETOOTH_STATE_CHANGED);
        registerReceiver(stateChangeReceiver, intentFilter);
    }

    private BroadcastReceiver stateChangeReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            int state = intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, BluetoothAdapter.ERROR);
            
            if (state == BluetoothAdapter.STATE_ON && isBondedDeviceExist()) { // If BT is on and there's a bonded device
                connectToLastPairedDevice(); // Try to automatically connect
            }
        }
    };

    private boolean isBondedDeviceExist() {
        return bluetoothAdapter.getBondState(SOME_PAIRED_DEVICE_ADDRESS) != BluetoothDevice.BOND_NONE;
    }

    private void connectToLastPairedDevice() {
        // Replace THIS_LINE with your actual paired device address
        BluetoothDevice device = bluetoothAdapter.getRemoteDevice("THIS_LINE");
        if (device != null) {
            device.connect();
        }
    }

    public void onDestroy() {
        unregisterReceiver(stateChangeReceiver);
    }
}

这个代码片段创建了一个接收器来监听蓝牙状态变化，当蓝牙打开并且有已配对设备时，尝试连接上上次配对的设备。注意，你需要替换`SOME_PAIRED_DEVICE_ADDRESS`为实际的已配对设备地址。

然而，具体的实现可能会因汽车厂商和Android版本的不同而有所差异，因为车机系统可能有自己的定制化需求和限制。在实际应用中，你可能需要获取权限、处理异常并适配各种情况。