Android判断sim卡状态

public String readSIMCard() {
            TelephonyManager tm = (TelephonyManager)this.getSystemService(TELEPHONY_SERVICE);//取得相关系统服务
        StringBuffer sb = new StringBuffer();
        switch(tm.getSimState()){ //getSimState()取得sim的状态  有下面6中状态
                case TelephonyManager.SIM_STATE_ABSENT :sb.append("无卡");break; 
                case TelephonyManager.SIM_STATE_UNKNOWN :sb.append("未知状态");break;
                case TelephonyManager.SIM_STATE_NETWORK_LOCKED :sb.append("需要NetworkPIN解锁");break;
                case TelephonyManager.SIM_STATE_PIN_REQUIRED :sb.append("需要PIN解锁");break;
                case TelephonyManager.SIM_STATE_PUK_REQUIRED :sb.append("需要PUK解锁");break;
                case TelephonyManager.SIM_STATE_READY :sb.append("良好");break;
        }
        
        if(tm.getSimSerialNumber()!=null){
                sb.append("@" + tm.getSimSerialNumber().toString());
        }else{
                sb.append("@无法取得SIM卡号");
        }
        
        if(tm.getSimOperator().equals("")){
                sb.append("@无法取得供货商代码");
        }else{
                sb.append("@" + tm.getSimOperator().toString());
        }
        
        if(tm.getSimOperatorName().equals("")){
                sb.append("@无法取得供货商");
        }else{
                sb.append("@" + tm.getSimOperatorName().toString());
        }
        
        if(tm.getSimCountryIso().equals("")){
                sb.append("@无法取得国籍");
        }else{
                sb.append("@" + tm.getSimCountryIso().toString());
        }
        
        if (tm.getNetworkOperator().equals("")) {
                sb.append("@无法取得网络运营商");
        } else {
                sb.append("@" + tm.getNetworkOperator());
        }
        if (tm.getNetworkOperatorName().equals("")) {
                sb.append("@无法取得网络运营商名称");
        } else {
                sb.append("@" + tm.getNetworkOperatorName());
        }
        if (tm.getNetworkType() == 0) {
                sb.append("@无法取得网络类型");
        } else {
                sb.append("@" + tm.getNetworkType());
        }
        return sb.toString();
    }