What is the best way to find and print signal strength of a cell phone in Android?

问题

This is the code I have so far that gathers the strength value, but when I try to print it in the main activity the emulator does not open the app. How would I fix this? My emulator is in API 29. On the emulator, it simply opens and then goes back to the home screen. I am also unsure of what to declare context to in the main. I currently have it set to null. My goal is to get the cellular signal strength from a cell phone and have this update multiple times every second within an app that I would create on the phone.

   public class SignalStrengthCdma extends Object implements Parcelable {


    public static String getSignalStrength(Context context) throws SecurityException {
        TelephonyManager telephonyManager = (TelephonyManager) context.getSystemService(Context.TELEPHONY_SERVICE);
        String strength = null;
        List<CellInfo> cellInfos = telephonyManager.getAllCellInfo();   //This will give info of all sims present inside your mobile
        if(cellInfos != null) {
            for (int i = 0 ; i < cellInfos.size() ; i++) {
                if (cellInfos.get(i).isRegistered()) {
                    if (cellInfos.get(i) instanceof CellInfoWcdma) {
                        CellInfoWcdma cellInfoWcdma = (CellInfoWcdma) cellInfos.get(i);
                        CellSignalStrengthWcdma cellSignalStrengthWcdma = cellInfoWcdma.getCellSignalStrength();
                        strength = String.valueOf(cellSignalStrengthWcdma.getDbm());
                    } else if (cellInfos.get(i) instanceof CellInfoGsm) {
                        CellInfoGsm cellInfogsm = (CellInfoGsm) cellInfos.get(i);
                        CellSignalStrengthGsm cellSignalStrengthGsm = cellInfogsm.getCellSignalStrength();
                        strength = String.valueOf(cellSignalStrengthGsm.getDbm());
                    } else if (cellInfos.get(i) instanceof CellInfoLte) {
                        CellInfoLte cellInfoLte = (CellInfoLte) cellInfos.get(i);
                        CellSignalStrengthLte cellSignalStrengthLte = cellInfoLte.getCellSignalStrength();
                        strength = String.valueOf(cellSignalStrengthLte.getDbm());
                    } else if (cellInfos.get(i) instanceof CellInfoCdma) {
                        CellInfoCdma cellInfoCdma = (CellInfoCdma) cellInfos.get(i);
                        CellSignalStrengthCdma cellSignalStrengthCdma = cellInfoCdma.getCellSignalStrength();
                        strength = String.valueOf(cellSignalStrengthCdma.getDbm());
                    }
                }
            }
        }
        return strength;
    }
}

来源：https://stackoverflow.com/questions/58665798/what-is-the-best-way-to-find-and-print-signal-strength-of-a-cell-phone-in-androi