android webservice接口调用问题

public String login(String uid ,String pwd){
String result=null;
// 设置需调用WebService接口需要传入的两个参数mobileCode、userId

    rpc.addProperty("uid", uid);
    rpc.addProperty("pwd",pwd);

    // 生成调用WebService方法的SOAP请求信息,并指定SOAP的版本  
    SoapSerializationEnvelope envelope = new SoapSerializationEnvelope(SoapEnvelope.VER10);  
    envelope.bodyOut = rpc;  
    // 等价于envelope.bodyOut = rpc;  
    envelope.setOutputSoapObject(rpc);  

    HttpTransportSE transport = new HttpTransportSE(url);  
    try {  
        // 调用WebService  
        transport.call(null, envelope);  
        result = envelope.getResponse().toString();
    } catch (Exception e) {  
        e.printStackTrace();  
    }  
    // 获取返回的数据  

// SoapObject object = (SoapObject) envelope.bodyIn;
// String result = object.getProperty("getMobileCodeInfoResult").toString();

return result;
}

在进行访问的时候 transport.call(null, envelope); 报错。
百度说是传值方式不对，，不知道是啥原因