With React Native, this app needs to:
Problem: #4 does not update on the screen.
This GIT link shows the current code.
Google explains the issue: "The useState hook in React does not update twice in a promise chain. This is because React batches state updates, meaning that all state updates that occur within a single event loop cycle are grouped together and applied at the end of the cycle. This helps to improve performance by avoiding unnecessary re-renders."
So maybe this button should call two Promises one after the other, with each one chained to a useState update. The second promise animation could have a delay of the same duration as the first animation, to make them consecutive. I haven't plugged this in yet to try it, will do so soon.
The animating functions look like this:
function updateNumCatsMoved(){
let newNumCats = { ... numCatsMoved };
newNumCats.value = newNumCats.value + 1;
setNumCatsMoved(newNumCats);
console.log("numCatsMoved:",numCatsMoved.value);
};
async function pressablePromise(){
new Promise(function(myResolve, myReject) {
cat1X.value = withTiming(cat1XEnd, config);
cat1Y.value = withTiming(cat1YEnd, config, () => {
runOnJS(myResolve)();
});
})
.then(function() { return updateNumCatsMoved();})
.then(
function() {
cat2X.value = withTiming(cat2XEnd, config);
cat2Y.value = withTiming(cat2YEnd, config, () => {
return;
});
}
)
// doesn't update on the screen
.then(function() { return updateNumCatsMoved();})
}
This was achieved by passing a value to the useState function. The value is the amount to update with. In my real app, the update can be -1, 0, or +1. This problem led to me learning about promises and how React batches state updates.
A bit of an issue to deal with moving forward is that the useState starts with 0 for both updates. I think I can use a local variable to help with that.
And so it WAS doing both updates, but they each started at 0. So it only went from 0 to 1.
function updateNumCatsMoved(n){
let newNumCats = { ... numCatsMoved };
newNumCats.value = newNumCats.value + n;
setNumCatsMoved(newNumCats);
};
function pressablePromise(){
new Promise(function(myResolve, myReject) {
cat1X.value = withTiming(cat1XEnd, config);
cat1Y.value = withTiming(cat1YEnd, config, () => {
runOnJS(myResolve)();
});
})
.then(function() { return updateNumCatsMoved(1);})
.then(
function() {
return new Promise((resolve, reject)=>{
cat2X.value = withTiming(cat2XEnd, config);
cat2Y.value = withTiming(cat2YEnd, config, () => {
runOnJS(resolve)();
});
})
}
)
.then(function() { return updateNumCatsMoved(2);})
}