我有一个写功能,基本上将数据添加到队列中,每500毫秒发送一次数据,并且我使用了setTimeouts来写数据,如下所示。而且我怀疑setTimeout的分析日志已被调用两次,我想知道是否有可能?可能的解决方法是什么?
import BleManager from 'react-native-ble-manager';
const BleManagerModule = NativeModules.BleManager;
const bleManagerEmitter = new NativeEventEmitter(BleManagerModule);
class bleHandler {
constructor() {
this.writeQueue = [];
bleManagerEmitter.addListener('BleManagerDidUpdateValueForCharacteristic', this.handleUpdateValueForCharacteristic);
}
//this function will be called when ble receives data from peripheral.
handleUpdateValueForCharacteristic(data){
// do something with data
//send ack that data is received.
this.writeData("AB:CD:EF:GH:IJ", " Some Important Message text ");
}
writeData(peripheralID, data) {
console.log("Adding data to Queue " + data);
if (this.writeQueue.length == 0) {
this.writeQueue.push(data);
setTimeout(() => this.sendData(peripheralID, data), 500);
} else
this.writeQueue.push(data);
console.log("New Queue Length = " + this.writeQueue.length);
}
sendData = (peripheralID, data) => {
if (data.length > 0 && peripheralID && this.writeQueue.length > 0) {
var byteBuf = this.formatData(data);
console.log("============" + slicedData + " and length = " + slicedData.length + " at Date = " + new Date().valueOf());
console.log("Writing Message : " + byteBuf );
this.handleWriteWithoutResponse(peripheralID, UUID, CHAR, byteBuf).then(() => {
console.log("success writing data ");
data = data.substring(PACKET_SIZE - 5);
if (data.length > 0) {
setTimeout(() => {
this.writeQueue[0] = data;
this.sendData(peripheralID, data)
}, 500);
} else {
this.writeQueue.shift();
setTimeout(() => {
if (this.writeQueue.length > 0)
this.sendData(peripheralID, this.writeQueue[0]);
}, 500);
}
}).catch((error) => {
console.log("error writing data ", error);
});
}
}
}
const bleModule = new bleHandler();
export default bleModule;
日志
11:13:28 log Adding data to Queue " Some Important Message text "
11:13:28 log New Queue Length = 1
11:13:28 log ============" Some Important Message text " and length = 28 at Date = 1597680808275
11:13:28 log Writing Message : 9876543211223A2243222C202233223A7B2241636B223A223230302212345
11:13:28 log ============" Some Important Message text " and length = 28 at Date = 1597680808276
11:13:28 log Writing Message : 9876543211223A2243222C202233223A7B2241636B223A223230302212345
11:13:28 log success writing data
11:13:28 log success writing data
现在,如果您查看IOS中的日志,我发现发送数据在(1597680808276-1597680808275)1 ms间隔内两次被调用,并且它是通过setTimeout函数调用的。 js中的setTimeout是否有问题?还是反应性问题或野生动物园问题?以及如何解决此问题。我已经看到几年前在nodejs中修复的类似问题。
注意:我正在使用react-native-ble-manager来发送/接收数据。
答案 0 :(得分:2)
此问题的根本原因是由于函数sendData
自身的调用。
sendData = (peripheralID, data) => {
if (data.length > 0 && peripheralID && this.writeQueue.length > 0) {
// ...
if (data.length > 0) {
setTimeout(() => {
// ...
this.sendData(peripheralID, data) ---> Recursive call
}, 500);
} else {
// ...
setTimeout(() => {
if (this.writeQueue.length > 0)
this.sendData(peripheralID, this.writeQueue[0]); ---> Recursive call
}, 500);
}
// ...
}
多次调用sendData的问题可以通过删除递归来解决
在此示例中,两个定时器回调(均计划在500ms之后发生)快速连续到达:
function example(a) {
console.log("example:", a, "at", Date.now());
if (a <= 3) {
setTimeout(() => {
example(a * 2);
}, 500);
}
}
// Schedule the calls
example(2);
example(3);
// Keep the thread busy
const end = Date.now() + 600;
while (Date.now() < end) {
}
注意如何
example: 4 at 1597923771329 example: 6 at 1597923771330
在时间上彼此紧邻。