文章目录

• 准备
• 接收蓝牙状态改变的广播
• 参考

Your application can listen for the ACTION_STATE_CHANGED broadcast intent, which the system broadcasts whenever the Bluetooth state changes. This broadcast contains the extra fields EXTRA_STATE and EXTRA_PREVIOUS_STATE, containing the new and old Bluetooth states, respectively. Possible values for these extra fields are STATE_TURNING_ON, STATE_ON, STATE_TURNING_OFF, and STATE_OFF. Listening for this broadcast can be useful if your app needs to detect runtime changes made to the Bluetooth state.

准备

IDE：

Android Studio 4.1.1
Build #AI-201.8743.12.41.6953283, built on November 5, 2020
Runtime version: 1.8.0_242-release-1644-b01 amd64
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o
Windows 10 10.0

接收蓝牙状态改变的广播

新建项目，选择 Empty Activity，在配置项目时，Minimum SDK 选择 API 16: Android 4.1 (Jelly Bean)。

编辑 src\main\AndroidManifest.xml 应用清单文件，声明使用 android.permission.BLUETOOTH 权限（第 4 行）：

<?xml version="1.0" encoding="utf-8"?>
<manifest ...>
    <!-- Allows applications to connect to paired bluetooth devices. -->
    <uses-permission android:name="android.permission.BLUETOOTH" />
</manifest>

编辑 MainActivity 文件：

package com.mk;

import android.bluetooth.BluetoothAdapter;
import android.content.BroadcastReceiver;
import android.content.Context;
import android.content.Intent;
import android.content.IntentFilter;
import android.os.Bundle;
import android.widget.Toast;

import androidx.appcompat.app.AppCompatActivity;

public class MainActivity extends AppCompatActivity {

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

        registerReceiver(broadcastReceiver, new IntentFilter(BluetoothAdapter.ACTION_STATE_CHANGED));
    }

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

        unregisterReceiver(broadcastReceiver);
    }

    private final BroadcastReceiver broadcastReceiver = new BroadcastReceiver() {
        @Override
        public void onReceive(Context context, Intent intent) {
            String action = intent.getAction();
            if (BluetoothAdapter.ACTION_STATE_CHANGED.equals(action)) {
                String currentState = null;
                switch (intent.getIntExtra(BluetoothAdapter.EXTRA_STATE, -1)) {
                    case BluetoothAdapter.STATE_TURNING_ON:
                        currentState = "BluetoothAdapter.STATE_TURNING_ON";
                        break;
                    case BluetoothAdapter.STATE_ON:
                        currentState = "BluetoothAdapter.STATE_ON";
                        break;
                    case BluetoothAdapter.STATE_TURNING_OFF:
                        currentState = "BluetoothAdapter.STATE_TURNING_OFF";
                        break;
                    case BluetoothAdapter.STATE_OFF:
                        currentState = "BluetoothAdapter.STATE_OFF";
                        break;
                    default:
                        currentState = "UNKNOWN";
                        break;
                }

                Toast.makeText(context, currentState, Toast.LENGTH_SHORT).show();

//                String previousState = null;
//                switch (intent.getIntExtra(BluetoothAdapter.EXTRA_PREVIOUS_STATE, -1)) {
//                    case BluetoothAdapter.STATE_TURNING_ON:
//                        previousState = "BluetoothAdapter.STATE_TURNING_ON";
//                        break;
//                    case BluetoothAdapter.STATE_ON:
//                        previousState = "BluetoothAdapter.STATE_ON";
//                        break;
//                    case BluetoothAdapter.STATE_TURNING_OFF:
//                        previousState = "BluetoothAdapter.STATE_TURNING_OFF";
//                        break;
//                    case BluetoothAdapter.STATE_OFF:
//                        previousState = "BluetoothAdapter.STATE_OFF";
//                        break;
//                    default:
//                        previousState = "UNKNOWN";
//                        break;
//                }
//
//                Toast.makeText(context, previousState, Toast.LENGTH_SHORT).show();
            }
        }
    };
}

参考

Broadcasts - Overview - Receiving broadcasts

Bluetooth - Overview - Set up bluetooth

Manifest.permission.BLUETOOTH

BluetoothAdapter.ACTION_STATE_CHANGED