How to use a method in render reactjs? - reactjs

Question

i have a method set_data which is used to set data based on id. I know it could be easy to call this set_data in componentdidupdate when id changes. However in doing so it doesnt set some state variables in the parent component.
To get rid of that want to call set_data method in render . However since this set_data method sets state of data it enters into an infinite loop in render . Also cannot provide a condition (like prevprops.id!== this.props.id) to execute set_data method.
To prevent it thought of using this set_data method not to set state at all. and can call this set_data method in render.
Below is the code,
export default class child extends React.Component {
state = {
query: '',
data: null,
};
empty_id = 0xffffffff;
componentDidMount() {
this.set_open_data();
}
componentDidUpdate(prevProps) {
if (prevProps.id !== this.props.id) {
this.set_data();
}
}
set_data = () => {
if (!this.props.info) {
return;
}
if (this.props.id === this.empty_id) {
this.setState({data: null});
return;
}
let data = {
info: [],
values: [],
};
const info = this.props.info;
for (let i=0, ii=info.length; i < ii; i++) {
if (info[i].meshes.includes(this.props.id)) {
const info = info[i].info;
const values = info[i].values;
data = {
info: typeof info === 'string' ? info.split('\r\n') : [],
values: values ? values : [],
};
break;
}
}
this.setState({data: this.filter_data(data, this.state.query)});
};
render = () => {
const shown_data= this.state.data;
/* i want to call set_data method here*/};}
Could someone help me solve this. Thanks.

Answer 1

You can't call setData there, because that would be anti-pattern. It will trigger a loop that will continuously render as well as keeps setting state.
You can probably rewrite the component this way:
export default class child extends React.Component {
state = {
query: ''
};
empty_id = 0xffffffff;
componentDidMount() {
this.set_open_data();
}
set_data = () => {
let data = {};
if (!this.props.info) {
return data;
}
if (this.props.id === this.empty_id) {
return data;
}
let data = {
info: [],
values: [],
};
const info = this.props.info;
for (let i=0, ii=info.length; i < ii; i++) {
if (info[i].meshes.includes(this.props.id)) {
const info = info[i].info;
const values = info[i].values;
data = {
info: typeof info === 'string' ? info.split('\r\n') : [],
values: values ? values : [],
};
break;
}
}
data = this.filter_data(data, this.state.query);
return data;
};
render = () => {
const shown_data= this.state.data;
const data = this.set_data();
/* i want to call set_data method here*/};}
In this, we are not setting data in the state. For every new ID, it will get new data and will compute it from render thereby avoiding antipattern. I have also removed componentDidMount, since we are doing computation in render. Note: This solution means taking away data from the state, if you are not using data anywhere before render, this will work.
Let me know if this helps.