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What happens after react calls setstate: 1. Merge the incoming parameter object with the current state of the component to trigger the reconciliation process; 2. Build the React element tree based on the new state and re-render the entire UI interface; 3. , after getting the element tree, React will calculate the node difference between the new tree and the old tree, and then minimize and re-render.
The operating environment of this tutorial: Windows 10 system, react17.0.1 version, Dell G3 computer.
React designed the setState method to re-render the page
Two ways to write setState() to update the state
setState(updater, [callback]), updater is a function that returns a stateChange object: (state, props) => stateChange The state and props received by stateChange are guaranteed to be the latest
setState(stateChange , [callback]), stateChange is an object, callback is an optional callback function, which is executed after the status is updated and the interface is updated.
Summary: The object method is the abbreviation of the function method if the new state does not depend on the original State ===> Use the object method if the new state depends on the original state ===> Use the function method if you need to get the latest state data after setState(), read it in the second callback function
What happens after calling setState?
After calling the setState function in the code, React will merge the passed parameter object with the current state of the component, and then trigger the so-called reconciliation process (Reconciliation).
After the reconciliation process, React will build the React element tree based on the new state in a relatively efficient way and proceed to re-render the entire UI interface.
After React obtains the element tree, React will automatically calculate the node difference between the new tree and the old tree, and then minimize and re-render the interface based on the difference.
In the difference calculation algorithm, React can relatively accurately know which positions have changed and how they should be changed, which ensures on-demand updates instead of full re-rendering.
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