Javascript 反应:this.setState不是一个函数
我正在为我遇到的另一个问题制定解决方案,但由此产生了“this.setState不是函数”错误。我找到了建议在构造函数中绑定它的答案,我做到了 这是我的构造函数的一部分:Javascript 反应:this.setState不是一个函数,javascript,reactjs,Javascript,Reactjs,我正在为我遇到的另一个问题制定解决方案,但由此产生了“this.setState不是函数”错误。我找到了建议在构造函数中绑定它的答案,我做到了 这是我的构造函数的一部分: this.newProject = this.newProject.bind(this); this.openProject = this.openProject.bind(this); this.saveProject = this.saveProject.bind(this); 这是我的职责: // Open a fil
this.newProject = this.newProject.bind(this);
this.openProject = this.openProject.bind(this);
this.saveProject = this.saveProject.bind(this);
这是我的职责:
// Open a file, set data as session item and reload page
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
read.onloadend = function() {
//sessionStorage.setItem("reloading", "true");
//sessionStorage.setItem("data", read.result);
//document.location.reload();
// Fix for missing data.
var jsonData = JSON.parse(read.result);
for (var i = 0; i < jsonData.blocks.length; i++) {
var name = jsonData.blocks[i].name;
var id = jsonData.blocks[i].id;
var ip = jsonData.blocks[i].ip;
var port = jsonData.blocks[i].port;
this.setState( { blockCount: (i + 1), });
// Add block to the list
this.setState({
blocks: this.state.blocks.concat({
id: id,
name: name,
ref: React.createRef(),
positionX: window.innerWidth*0.4 - 125 / 2,
positionY: 75 + ( 50 * this.state.blocks.length),
links:[],
requires: this.state.parameters.blockRequires
})
});
}
}
}
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
var that = this;
read.onloadend = function() {
// ...
that.setState(/*... etc*/
//打开文件,将数据设置为会话项并重新加载页面
openProject(文件对象){
var read=new FileReader();
read.readAsBinaryString(FileObject);
read.onloadend=函数(){
//setItem(“重新加载”、“true”);
//setItem(“数据”,read.result);
//document.location.reload();
//修复丢失的数据。
var jsonData=JSON.parse(read.result);
对于(var i=0;i
解决此问题的方法是什么?
此
属于最接近的函数上下文,在您的情况下是read.onloadend=function()
…而不是类
您可以通过在输入特殊函数之前将类级别this
分配给新变量来解决此问题:
// Open a file, set data as session item and reload page
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
read.onloadend = function() {
//sessionStorage.setItem("reloading", "true");
//sessionStorage.setItem("data", read.result);
//document.location.reload();
// Fix for missing data.
var jsonData = JSON.parse(read.result);
for (var i = 0; i < jsonData.blocks.length; i++) {
var name = jsonData.blocks[i].name;
var id = jsonData.blocks[i].id;
var ip = jsonData.blocks[i].ip;
var port = jsonData.blocks[i].port;
this.setState( { blockCount: (i + 1), });
// Add block to the list
this.setState({
blocks: this.state.blocks.concat({
id: id,
name: name,
ref: React.createRef(),
positionX: window.innerWidth*0.4 - 125 / 2,
positionY: 75 + ( 50 * this.state.blocks.length),
links:[],
requires: this.state.parameters.blockRequires
})
});
}
}
}
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
var that = this;
read.onloadend = function() {
// ...
that.setState(/*... etc*/
当然,您需要将onloadend
回调函数中this
的所有实例更改为that
(或您选择的任何变量名称)
*编辑:正如@MDTabishMahfuz所描述的,您还可以使用,因为与函数
声明不同,箭头函数:
// Open a file, set data as session item and reload page
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
read.onloadend = function() {
//sessionStorage.setItem("reloading", "true");
//sessionStorage.setItem("data", read.result);
//document.location.reload();
// Fix for missing data.
var jsonData = JSON.parse(read.result);
for (var i = 0; i < jsonData.blocks.length; i++) {
var name = jsonData.blocks[i].name;
var id = jsonData.blocks[i].id;
var ip = jsonData.blocks[i].ip;
var port = jsonData.blocks[i].port;
this.setState( { blockCount: (i + 1), });
// Add block to the list
this.setState({
blocks: this.state.blocks.concat({
id: id,
name: name,
ref: React.createRef(),
positionX: window.innerWidth*0.4 - 125 / 2,
positionY: 75 + ( 50 * this.state.blocks.length),
links:[],
requires: this.state.parameters.blockRequires
})
});
}
}
}
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
var that = this;
read.onloadend = function() {
// ...
that.setState(/*... etc*/
没有自己对此
或超级
此
属于最接近的函数上下文,在您的情况下是read.onloadend=function()
…而不是类
您可以通过在输入特殊函数之前将类级别this
分配给新变量来解决此问题:
// Open a file, set data as session item and reload page
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
read.onloadend = function() {
//sessionStorage.setItem("reloading", "true");
//sessionStorage.setItem("data", read.result);
//document.location.reload();
// Fix for missing data.
var jsonData = JSON.parse(read.result);
for (var i = 0; i < jsonData.blocks.length; i++) {
var name = jsonData.blocks[i].name;
var id = jsonData.blocks[i].id;
var ip = jsonData.blocks[i].ip;
var port = jsonData.blocks[i].port;
this.setState( { blockCount: (i + 1), });
// Add block to the list
this.setState({
blocks: this.state.blocks.concat({
id: id,
name: name,
ref: React.createRef(),
positionX: window.innerWidth*0.4 - 125 / 2,
positionY: 75 + ( 50 * this.state.blocks.length),
links:[],
requires: this.state.parameters.blockRequires
})
});
}
}
}
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
var that = this;
read.onloadend = function() {
// ...
that.setState(/*... etc*/
当然,您需要将onloadend
回调函数中this
的所有实例更改为that
(或您选择的任何变量名称)
*编辑:正如@MDTabishMahfuz所描述的,您还可以使用,因为与函数
声明不同,箭头函数:
// Open a file, set data as session item and reload page
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
read.onloadend = function() {
//sessionStorage.setItem("reloading", "true");
//sessionStorage.setItem("data", read.result);
//document.location.reload();
// Fix for missing data.
var jsonData = JSON.parse(read.result);
for (var i = 0; i < jsonData.blocks.length; i++) {
var name = jsonData.blocks[i].name;
var id = jsonData.blocks[i].id;
var ip = jsonData.blocks[i].ip;
var port = jsonData.blocks[i].port;
this.setState( { blockCount: (i + 1), });
// Add block to the list
this.setState({
blocks: this.state.blocks.concat({
id: id,
name: name,
ref: React.createRef(),
positionX: window.innerWidth*0.4 - 125 / 2,
positionY: 75 + ( 50 * this.state.blocks.length),
links:[],
requires: this.state.parameters.blockRequires
})
});
}
}
}
openProject(FileObject) {
var read = new FileReader();
read.readAsBinaryString(FileObject);
var that = this;
read.onloadend = function() {
// ...
that.setState(/*... etc*/
没有自己对此
或超级
绑定对于类的函数来说这是必需的,但是您有一个额外的回调(
onloadend函数
),它是一个不同的函数,并且组件的this
在那里不可用
JS中的常规函数在其上下文中对此有自己的解释。您可以使用@David784建议的方法,也可以对onloadend
处理程序使用箭头函数,如下所示:
read.onloadend = () => {
....
this.setState(....);
....
}
Arrow函数从父函数的上下文中有此函数,即您案例中的React组件。绑定这对于类的函数是必需的,但是您有一个额外的回调(
onloadend函数
),它是一个不同的函数,并且组件的this
在那里不可用
JS中的常规函数在其上下文中对此有自己的解释。您可以使用@David784建议的方法,也可以对onloadend
处理程序使用箭头函数,如下所示:
read.onloadend = () => {
....
this.setState(....);
....
}
Arrow函数从父对象的上下文(即案例中的React组件)中具有此属性