Android P系统设置之默认选择网络类型(4G，3G，2G)

frameworks\base\telephony\java\com\android\internal\telephony\RILConstants.java
build\make\tools\buildinfo.sh

buildinfo.sh中增加：

echo "ro.telephony.default_network=11"

网络类型定义：
frameworks\base\telephony\java\com\android\internal\telephony\RILConstants.java

/* NETWORK_MODE_* See ril.h RIL_REQUEST_SET_PREFERRED_NETWORK_TYPE */
int NETWORK_MODE_WCDMA_PREF     = 0; /* GSM/WCDMA (WCDMA preferred) */
int NETWORK_MODE_GSM_ONLY       = 1; /* GSM only */
int NETWORK_MODE_WCDMA_ONLY     = 2; /* WCDMA only */
int NETWORK_MODE_GSM_UMTS       = 3; /* GSM/WCDMA (auto mode, according to PRL)
                                       AVAILABLE Application Settings menu*/
int NETWORK_MODE_CDMA           = 4; /* CDMA and EvDo (auto mode, according to PRL)
                                       AVAILABLE Application Settings menu*/
int NETWORK_MODE_CDMA_NO_EVDO   = 5; /* CDMA only */
int NETWORK_MODE_EVDO_NO_CDMA   = 6; /* EvDo only */
int NETWORK_MODE_GLOBAL         = 7; /* GSM/WCDMA, CDMA, and EvDo (auto mode, according to PRL)
                                       AVAILABLE Application Settings menu*/
int NETWORK_MODE_LTE_CDMA_EVDO  = 8; /* LTE, CDMA and EvDo */
int NETWORK_MODE_LTE_GSM_WCDMA  = 9; /* LTE, GSM/WCDMA */
int NETWORK_MODE_LTE_CDMA_EVDO_GSM_WCDMA = 10; /* LTE, CDMA, EvDo, GSM/WCDMA */
int NETWORK_MODE_LTE_ONLY       = 11; /* LTE Only mode. */
int NETWORK_MODE_LTE_WCDMA      = 12; /* LTE/WCDMA */
int NETWORK_MODE_TDSCDMA_ONLY            = 13; /* TD-SCDMA only */
int NETWORK_MODE_TDSCDMA_WCDMA           = 14; /* TD-SCDMA and WCDMA */
int NETWORK_MODE_LTE_TDSCDMA             = 15; /* TD-SCDMA and LTE */
int NETWORK_MODE_TDSCDMA_GSM             = 16; /* TD-SCDMA and GSM */
int NETWORK_MODE_LTE_TDSCDMA_GSM         = 17; /* TD-SCDMA,GSM and LTE */
int NETWORK_MODE_TDSCDMA_GSM_WCDMA       = 18; /* TD-SCDMA, GSM/WCDMA */
int NETWORK_MODE_LTE_TDSCDMA_WCDMA       = 19; /* TD-SCDMA, WCDMA and LTE */
int NETWORK_MODE_LTE_TDSCDMA_GSM_WCDMA   = 20; /* TD-SCDMA, GSM/WCDMA and LTE */
int NETWORK_MODE_TDSCDMA_CDMA_EVDO_GSM_WCDMA  = 21; /*TD-SCDMA,EvDo,CDMA,GSM/WCDMA*/
int NETWORK_MODE_LTE_TDSCDMA_CDMA_EVDO_GSM_WCDMA = 22; /* TD-SCDMA/LTE/GSM/WCDMA, CDMA, and EvDo */
int PREFERRED_NETWORK_MODE = Integer.parseInt(TelephonyManager.getTelephonyProperty(0,
       "ro.telephony.default_network", Integer.toString(NETWORK_MODE_WCDMA_PREF)));

网络类型4G，3G和2G的判断参考：

/**
 * 判断移动网络的类型
 * 
 * @param networkType
 * @return 移动网络类型
 */
private static final int getNetworkClass(int networkType) {
    switch (networkType) {
    case TelephonyManager.NETWORK_TYPE_GPRS:
    case TelephonyManager.NETWORK_TYPE_EDGE:
    case TelephonyManager.NETWORK_TYPE_CDMA:
    case TelephonyManager.NETWORK_TYPE_1xRTT:
    case TelephonyManager.NETWORK_TYPE_IDEN:
        return NETWORK_2G;
    case TelephonyManager.NETWORK_TYPE_UMTS:
    case TelephonyManager.NETWORK_TYPE_EVDO_0:
    case TelephonyManager.NETWORK_TYPE_EVDO_A:
    case TelephonyManager.NETWORK_TYPE_HSDPA:
    case TelephonyManager.NETWORK_TYPE_HSUPA:
    case TelephonyManager.NETWORK_TYPE_HSPA:
    case TelephonyManager.NETWORK_TYPE_EVDO_B:
    case TelephonyManager.NETWORK_TYPE_EHRPD:
    case TelephonyManager.NETWORK_TYPE_HSPAP:
        return NETWORK_3G;
    case TelephonyManager.NETWORK_TYPE_LTE:
        return NETWORK_4G;
    default:
        return NETWORK_UNKNOW;
    }
}

参考文献：
https://blog.csdn.net/mxiaoyem/article/details/50857008