设置里首选网络类型由3G改成4G

Android首选网络类型默认修改

1.源码路径：androidm/frameworks/base/packages/SettingsProvider/src/com/android/providers/settings/DatabaseHelper.java

 // Set the preferred network mode to target desired value or Default
            // value defined in RILConstants
            int type;
            type = RILConstants.PREFERRED_NETWORK_MODE;
            loadSetting(stmt, Settings.Global.PREFERRED_NETWORK_MODE, type);

2.源码路径：
androidm/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      = SystemProperties.getInt("ro.telephony.default_network",
            NETWORK_MODE_LTE_TDSCDMA_CDMA_EVDO_GSM_WCDMA);

#把对应位置修改成如下即可成功：

 int PREFERRED_NETWORK_MODE      = SystemProperties.getInt("ro.telephony.default_network",
            NETWORK_MODE_LTE_TDSCDMA_CDMA_EVDO_GSM_WCDMA);