NGRX选择器多次返回相同的值
一个
export const selectIDs = creteSelector(
selectorFeature,
(feature: Feature) => {
return feature?.metadata?.ids || []
}
}
当系统启动时，我有一个组件中的
this.store.select(selectIDs).subscribe((ids) => dosomething(ids))
组件是undefined so []传递到回调中。然后功能然后更改为正常值，但.metadata不可用，因此选择与最后结果相同的returns []，因此dosomething（）不应该回电称为。但是，实际上，它在我的代码中再次被调用[]
我的问题是，是否两个时间选择器返回[]，是否应该调用一次calllback（subscribe中的这些调用）？
还是我的意思是，如果我这样做：
this.store.select(featueSelector).subscribe((feature) => console.log(feature)
假设全局状态更改了10次，但是功能保持不变，那么功能以元素为单位返回相同的功能，console.log（）是否可以称为10次？我想只有在哪个功能Selectore返回与上次不同时，才会调用Console.log（）？
谢谢
====================================== 事实证明this.store.select（）返回可观察，因此，当观察者调用next（）> console时。 log（）将被调用。
NGRX选择器记忆意味着如果输入相同，它将直接返回相同的值。
I have a
export const selectIDs = creteSelector(
selectorFeature,
(feature: Feature) => {
return feature?.metadata?.ids || []
}
}
in the component I have
this.store.select(selectIDs).subscribe((ids) => dosomething(ids))
When the system is up feature is undefined so [] is passed into the callback. Then feature then changes to a normal value but .metadata not available so select returns [] which is same as last result so the dosomething() call back is not supposed to be called. But it actually get called again in my code with []
My question is if both time selector returns a [], shouldn't the calllback (those calls in subscribe)be called once?
Or generally I mean if I do this:
this.store.select(featueSelector).subscribe((feature) => console.log(feature)
suppose global state changes 10 times, but feature stays same so featureSelector returns same feature, will the console.log() be called 10 times? I imagine the console.log() will only be called when what feature selectore returns is different from last time?
Thanks
=================== updated =============
it turns out this.store.select() returns a observable, so when the obserable calls the next(), console.log() will be called.
Ngrx selector memorize means it directly returns same value if input is same.
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选择器再次触发，并返回一个新的数组实例。
因为
[] === []是虚假的，所以新实例传递给订阅方法。作为解决方法，您可以：
this.store.select（）。pipe（filter（arr =＆gt; arr.length＆gt; 0））。subscribe（））this.store.select（）。pipe（dimstand（insertcheckhere））。subscribe（））const emptle = []并返回选择器中的空而不是[]The selector is fired again, and a new array instance is returned.
Because
[] === []is falsy, the new instance is passed to the subscribe method.As a workaround, you can:
this.store.select().pipe(filter(arr => arr.length > 0 )).subscribe())this.store.select().pipe(distinct(insertCheckHere)).subscribe())const empty = []and returnemptyin the selector instead of[]