远程控制led实验中 returnValue 的中用

hgmyaoming

这是远程控制led灯的实验，在读代码的时对这句不怎么理解" String returnValue = ""    ",跟后面这段代码
if (client.available()) {
      char c = client.read();
      Serial.print(c);
        if (c == '{')
          ResponseBegin = true;
        else if (c == '}')
          ResponseBegin = false;
  
        if (ResponseBegin)
          returnValue += c;   
    }
    if (returnValue.length() !=0 && (ResponseBegin == false))
    {
      Serial.println(returnValue);
      
      if (returnValue.charAt(returnValue.length() - 1) == '1') {
        Serial.println("turn on the LED");
        digitalWrite(5, HIGH);
      }
        else if(returnValue.charAt(returnValue.length() - 1) == '0') {
        Serial.println("turn off the LED");
        digitalWrite(5, LOW);
      }
       returnValue = "";


的思路不怎么理解， returnValue 这个值有几次变更，其中有什么意义也不是很清楚，希望给我前辈多多指教。



  /*
   Yeelink sensor client power switch example
   */

  #include <SPI.h>
  #include <Ethernet.h>
  #include <Wire.h>
  #include <math.h>

  byte buff[2];

  /* for yeelink api, the initialze of the Yeelink including apikey ,device num ,sensor num,
  serv num, local MAC .Yeelink ip.  the time of the tow mesamges */
  #define APIKEY         "c142a1e19dec73dd5dde48309ad20590" // 此处替换为你自己的API KEY
  #define DEVICEID       19112 // 此处替换为你的设备编号
  #define SENSORID1      33270 // 此处替换为你的传感器编号


  // assign a MAC address for the ethernet controller.
  byte mac[] = { 0x00, 0x1D, 0x72, 0x82, 0x35, 0x9D};
  // initialize the library instance:
  EthernetClient client ;
  char server[] = "api.yeelink.net";   // name address for yeelink API

  unsigned long lastConnectionTime = 0;          // last time you connected to the server, in milliseconds
  boolean lastConnected = false;                 // state of the connection last time through the main loop
  const unsigned long postingInterval = 3*1000; // delay between 2 datapoints, 30s
  String returnValue = "";
  boolean ResponseBegin = false;

  void setup() {
    pinMode(5, OUTPUT);
    Wire.begin();
    // start serial port:
   Serial.begin(57600);

    // start the Ethernet connection with DHCP:
    if (Ethernet.begin(mac) == 0) {
      Serial.println("Failed to configure Ethernet using DHCP");
      for(;;)
        ;
    }
    else {
      Serial.println("Ethernet configuration OK");
    }
  }

  void loop() {
    // if there's incoming data from the net connection.
    // send it out the serial port.  This is for debugging
    // purposes only:

    if (client.available()) {
      char c = client.read();
      Serial.print(c);
        if (c == '{')
          ResponseBegin = true;
        else if (c == '}')
          ResponseBegin = false;

        if (ResponseBegin)
          returnValue += c;   
    }
    if (returnValue.length() !=0 && (ResponseBegin == false))
    {
      Serial.println(returnValue);

      if (returnValue.charAt(returnValue.length() - 1) == '1') {
        Serial.println("turn on the LED");
        digitalWrite(5, HIGH);
      }
        else if(returnValue.charAt(returnValue.length() - 1) == '0') {
        Serial.println("turn off the LED");
        digitalWrite(5, LOW);
      }
       returnValue = "";
    }
    // if there's no net connection, but there was one last time
    // through the loop, then stop the client:
    if (!client.connected() && lastConnected) {
      Serial.println();
      Serial.println("disconnecting.");
      client.stop();
    }

    // if you're not connected, and ten seconds have passed since
    // your last connection, then connect again and send data:
    if(!client.connected() && (millis() - lastConnectionTime > postingInterval)) {
      // read sensor data, replace with your code
      //int sensorReading = readLightSensor();
      Serial.print("yeelink:");
      //get data from server  
      getData();
    }
    // store the state of the connection for next time through
    // the loop:
    lastConnected = client.connected();
  }



  // this method makes a HTTP connection to the server and get data back
  void getData(void) {
    // if there's a successful connection:
    if (client.connect(server, 80)) {
      Serial.println("connecting...");
      // send the HTTP GET request:

      client.print("GET /v1.0/device/");
      client.print(DEVICEID);
      client.print("/sensor/");
      client.print(SENSORID1);
      client.print("/datapoints");
      client.println(" HTTP/1.1");
      client.println("Host: api.yeelink.net");
      client.print("Accept: *");
      client.print("/");
      client.println("*");
      client.print("U-ApiKey: ");
      client.println(APIKEY);
      client.println("Content-Length: 0");
      client.println("Connection: close");
      client.println();
      Serial.println("print get done.");

    }
    else {
      // if you couldn't make a connection:
      Serial.println("connection failed");
      Serial.println();
      Serial.println("disconnecting.");
      client.stop();
    }
     // note the time that the connection was made or attempted:
    lastConnectionTime = millis();
  }

sailor0908

这个就是赋一个空值给 returnValue .