我正在查询一个使用NodeMCU ESP8266微控制器返回JSON字符串的网页。该网页的响应如下所示:
{"1":true,"2":false,"3":false,"4":true,"5":true,"6":false,"7":false,"8":false}
我正在使用的代码如下:
#include <ESP8266WiFi.h>
#include <ESP8266HTTPClient.h>
#include <ArduinoJson.h>
String payload = "";
const char* ssid = "ssid";
const char* password = "password";
String url = "example.com/data.json";
void setup() {
Serial.begin(115200);
delay(2000); while (!Serial);
WiFi.begin(ssid, password);
while (WiFi.status() !=WL_CONNECTED){
delay(500);
Serial.print(".");
}
Serial.println(WiFi.localIP());
pinMode(D0, OUTPUT);
}
void loop() {
StaticJsonBuffer<100> jsonBuffer;
delay(5000);
HTTPClient http;
http.begin(url);
int httpCode = http.GET();
Serial.println(httpCode);
Serial.println(http.getString());
if (httpCode > 0) {
payload = http.getString();
}
http.end();
JsonObject& root = jsonBuffer.parseObject(payload);
Serial.println(payload);
if(!root.success()) {
Serial.println("parseObject() failed");
}
if(root["1"] == true) {
Serial.println("true");
}
digitalWrite(D0, !digitalRead(D0));
}
我相信它无法解析的原因是有效负载变量以尾随换行符结尾。然后,我尝试了payload = payload.trim();
,但后来得到了no match for 'operator=' (operand types are 'String' and 'void')
,所以我尝试了payload = payload.replace("\n,"");
相同的问题,然后又尝试了payload = String(payload);
,失败了。我在做什么错了?
答案 0 :(得分:0)
就像有人说的那样,trim
和replace
不返回String
。它“返回” void
,错误消息告诉您您正在尝试将无效返回值分配给String。放置payload.trim();
就足够了。 payload.replace("\n","");
但是payload.trim();
和payload.replace("\n","");
做的事情不同。如文档中所述,trim()
删除尾随空格和前导空格,而replace("\n","")
则删除字符串中的所有(唯一)换行符,即使在中间也是如此。
空格通常是指空格,换行符,制表符和其他一些其他字符。