ReactJS更新状态数组中的单个对象 [英] ReactJS updating a single object inside a state array

问题描述

我有一个名为 this.state.devices 的状态，它是 device 对象的数组.

I have a state called this.state.devices which is an array of device objects.

说我有一个功能

updateSomething: function (device) {
    var devices = this.state.devices;
    var index = devices.map(function(d){
        return d.id;
    }).indexOf(device.id);

    if (index !== -1) {
       // do some stuff with device
       devices[index] = device;
       this.setState({devices:devices});
    }
}

这里的问题是，每次调用 this.updateSomething 时，整个数组都会更新，因此整个DOM都将重新呈现.在我的情况下，这导致浏览器冻结，因为我几乎每秒都要调用此函数，并且有许多 device 对象.但是，在每次通话中，这些设备中只有一个或两个实际上被更新.

Problem here is that every time this.updateSomething is called, the entire array is updated, and so the entire DOM gets re-rendered. In my situation, this causes the browser to freeze as I am calling this function pretty every second, and there are many device objects. However, on every call, only one or two of these devices are actually updated.

我有什么选择?

编辑

根据我的实际情况，设备是一个定义如下的对象:

In my exact situation, a device is an object that is defined as follows:

function Device(device) {
    this.id = device.id;
    // And other properties included
}

因此， state.devices 数组中的每个项目都是该 Device 的特定时刻，即我所拥有的某个地方:

So each item in the array of state.devices is a specific instant of this Device, i.e. somewhere I'd have:

addDevice: function (device) {
    var newDevice = new Device(device);
    this.setState({devices: this.state.devices.push(device)});
}

我更新后的答案如何进行 updateSomething ，我有:

My updated answer how on to updateSomething, I have:

updateSomething: function (device) {
    var devices = this.state.devices;
    var index = devices.map(function(d){
        return d.id;
    }).indexOf(device.id);

    if (index !== -1) {
       // do some stuff with device
       var updatedDevices = update(devices[index], {someField: {$set: device.someField}});
       this.setState(updatedDevices);
    }
}

现在的问题是，我得到一个错误，提示无法读取 id 的未定义值，并且该错误来自函数Device()；似乎正在调用新的 new Device()，并且没有将 device 传递给它.

Problem now is that I get an error that says cannot read the undefined value of id, and it is coming from the function Device(); it seems that a new new Device() is being called and the device is not passed to it.

推荐答案

您可以使用react 不变性助手.

You can use the react immutability helpers.

从文档中

简单推送

var initialArray = [1, 2, 3];
var newArray = update(initialArray, {$push: [4]}); // => [1, 2, 3, 4]

initialArray仍为[1、2、3].

因此，在您的示例中，您将需要执行以下操作:

So for your example you will want to do something like this:

if (index !== -1) {
    var deviceWithMods = {}; // do your stuff here
    this.setState(update(this.state.devices, {index: {$set: deviceWithMods }}));
}

根据您的 device 模型的复杂程度，您可以就地修改"对象属性:

Depending on how complex your device model is you could just 'modify' the object properties in situ:

if (index !== -1) {
    this.setState(update(this.state.devices[index], {name: {$set: 'a new device name' }}));
}

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