Android 獲取網絡信號強度的完整方法 (WiFi 與移動網絡)

在 Android 中獲取網絡信號強度，需區分 WiFi 和移動網絡 (2G/3G/4G/5G) 使用不同 API，並注意權限與版本差異。

核心代碼實現

1. 檢查網絡連接類型

ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkInfo activeInfo = cm.getActiveNetworkInfo();

if (activeInfo == null || !activeInfo.isConnected()) {
    // 無網絡連接
    return;
}

int networkType = activeInfo.getType(); // TYPE_WIFI, TYPE_MOBILE 等

2. WiFi 信號強度 (API 1+)

WifiManager wifiManager = (WifiManager) getApplicationContext().getSystemService(Context.WIFI_SERVICE);

// 方法一：掃描結果獲取 (需位置權限 Android 6+)
List scanResults = wifiManager.getScanResults();
for (ScanResult result : scanResults) {
    if (result.BSSID.equals(currentBSSID)) {
        int level = result.level; // dBm 值，如 -50 到 -100
        // 或使用 WifiManager.calculateSignalLevel(level, numLevels) 獲取 0-4 級
        break;
    }
}

// 方法二：當前連接信息 (API 23+ 推薦)
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
    WifiInfo wifiInfo = wifiManager.getConnectionInfo();
    int rssi = wifiInfo.getRssi(); // dBm
    int linkSpeed = wifiInfo.getLinkSpeed(); // Mbps
}

3. 移動網絡信號強度

TelephonyManager tm = (TelephonyManager) getSystemService(Context.TELEPHONY_SERVICE);

// API 31+ (Android 12) 統一 API
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.S) {
    // 需 READ_PHONE_STATE 權限
    @SuppressLint("MissingPermission")
    SignalStrength signalStrength = tm.getSignalStrength();
    
    // 5G
    if (signalStrength.isNr()) {
        CellSignalStrengthNr nr = signalStrength.getCellSignalStrengths(CellSignalStrengthNr.class).get(0);
        int ssRsrp = nr.getSsRsrp(); // dBm
    }
    // 4G
    CellSignalStrengthLte lte = signalStrength.getCellSignalStrengths(CellSignalStrengthLte.class).get(0);
    int rsrp = lte.getRsrp(); // dBm
    int rsrq = lte.getRsrq(); // dB
    // 3G/2G 類似...
}

// API 17-30 兼容方案
PhoneStateListener listener = new PhoneStateListener() {
    @Override
    public void onSignalStrengthsChanged(SignalStrength signalStrength) {
        super.onSignalStrengthsChanged(signalStrength);
        // 反射獲取私有方法或使用舊 API
        // signalStrength.getGsmSignalStrength() 等
    }
};
tm.listen(listener, PhoneStateListener.LISTEN_SIGNAL_STRENGTHS);

信號強度等級轉換 (通用)

// 將 dBm 轉換為 0-4 級顯示圖標
public static int getSignalLevel(int rssi, int networkType) {
    // WiFi: -50 優秀, -100 差
    // 移動網絡: -80 優秀, -110 差 (視制式)
    
    if (networkType == ConnectivityManager.TYPE_WIFI) {
        return WifiManager.calculateSignalLevel(rssi, 5); // 0-4
    } else {
        // 移動網絡簡易分級
        if (rssi >= -80) return 4;
        else if (rssi >= -90) return 3;
        else if (rssi >= -100) return 2;
        else if (rssi >= -110) return 1;
        else return 0;
    }
}

所需權限

<uses-permission android:name="android.permission.ACCESS_NETWORK_STATE" />
<uses-permission android:name="android.permission.ACCESS_WIFI_STATE" />
<uses-permission android:name="android.permission.READ_PHONE_STATE" /> <!-- 移動網絡信號需此權限 -->
<uses-permission android:name="android.permission.ACCESS_FINE_LOCATION" /> <!-- Android 6+ WiFi 掃描需位置權限 -->

版本適配總結表

現代最佳實踐：NetworkCallback (API 24+)

ConnectivityManager cm = (ConnectivityManager) getSystemService(Context.CONNECTIVITY_SERVICE);
NetworkRequest request = new NetworkRequest.Builder()
    .addCapability(NetworkCapabilities.NET_CAPABILITY_INTERNET)
    .build();

cm.registerNetworkCallback(request, new ConnectivityManager.NetworkCallback() {
    @Override
    public void onAvailable(@NonNull Network network) {
        NetworkCapabilities nc = cm.getNetworkCapabilities(network);
        if (nc != null) {
            // nc.getSignalStrength() API 28+ 統一獲取信號強度
            // nc.getTransportType() 判斷 TRANSPORT_WIFI / TRANSPORT_CELLULAR
        }
    }
    // onLost, onCapabilitiesChanged...
});