RxSwift教程 (warnings)

本文详细解释了RxSwift中未使用的订阅和未使用的可观察序列警告的原因及如何避免这些问题。介绍了使用DisposeBag和takeUntil操作符来确保资源正确释放的方法。

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referingTo:https://github.com/ReactiveX/RxSwift/blob/master/Documentation/Warnings.md
Warnings(Unused disposable。The following is valid for the subscribe*, bind* and drive* family of functions that return Disposable.You will receive a warning for doing something such as this:)
let xs: Observable…
xs
.filter{…}
.map{…}
.switchLatest()
.subscribe(onNext: {

}, onError: {
///
})
The subscribe function returns a subscription Disposable that cn be used to cancel computation and free resources.However,not using it(and thus not disposing it)will result in an error.
The preferred way of termiating these fluent calls is by using a DisposeBag,either through chaining a call to .disposed(by: disposeBag)or by adding the disposable directly to the bag.
let xs: Observable…
let disposeBag = DisposeBag()
xs
.filter {…}
.map{…}
.switchLatest()
.subscribe(onNext: {
} ,onError:{

})
.disposed(by:disposeBag)//note .disposed(by:)
When disposeBag gets deallocated,the disposables contained within it will be automatically disposed as well.In the case where xs terminates in a predictable way with either a completed or Error message,not handling the subscription Disposable won’t leak any resources.However,even in this case,using a dispose bag is still the preferred way to handle subscription disposables.It ensures that element computation is always terminated at a predictable moment, and makes your code robust and future proof because resources will be properly disposed even if the implementation of xs changes.
Another way to make sure subscriptions and resources and tied to the lifetime of some object is by using the takeUtil operator.
let xs: Observable…
let someObject: NSObject…
_ = xs
.filter{}
.map{}
.switchLatest()
.takeUtil(someObject.deallocated)
.subscribe(onNext: {
///
}, onError:{
///
})
if ignoring the subscription Disposable is the desired behavior,this is how to silence the compiler warning.
let xs: Observable…
_ = xs//note the underscorre
.filter{}
.map{}
.switchLatest()
.subscribe(onNext:{
}, onError :{
})
Unused observable sequence(unused-observable)
You will receive a warning for doing something such as this:
let xs: Observable…
xs
.filter{}
.map{}
This code defines an observable sequence that is filtered and mapped from the xs sequence but then ignores the result.Sincethis code just defines an observable sequence and then ignores it, it doesn’t actually do anything.Your intention was probably to either store the observable sequence definition and use it later…
let xs: Observable…
let ys = xs//names definition as ys
.filter{}
.map{}
or start computation based on that definition
let xs: Observable…
let disposeBag = DisposeBag()
xs
.filter{}
.map{}
.subscribe(onNext: { nextElement in
print(nextElement)
})
.disposed(by:disposeBag)

### 使用 `warnings.catch_warnings` 的方法 Python 中的 `warnings` 模块提供了一种灵活的方式来处理警告信息。通过使用 `catch_warnings` 上下文管理器,可以在特定代码块中临时更改警告过滤设置。 #### 基本用法 要捕获并控制警告,可以使用如下方式: ```python import warnings with warnings.catch_warnings(): warnings.simplefilter("ignore") # 忽略所有警告 # 可能触发警告的代码放在这里 ``` 如果希望记录所有的警告而不是忽略它们,则可以这样做[^1]: ```python import warnings with warnings.catch_warnings(record=True) as w: # 引发警告的操作 warnings.warn("A warning occurred!") # 处理被捕获的警告列表 assert len(w) == 1 assert issubclass(w[-1].category, UserWarning) assert "occurred" in str(w[-1].message) ``` 对于更复杂的场景,比如只针对某些类型的警告采取行动或者自定义响应行为,可以通过调整简单筛选器参数来实现更加精细的控制。 例如,仅捕捉 DeprecationWarning 类型的警告而不影响其他类型的警告: ```python import warnings with warnings.catch_warnings(): warnings.filterwarnings('error', category=DeprecationWarning) try: # 这里放置可能引发 DeprecationWarning 的代码 pass except DeprecationWarning as e: print(f"Catched deprecation warning: {e}") ``` 上述例子展示了如何利用 `warnings.catch_warnings()` 来管理和应对程序运行期间产生的各种警告消息,从而提高代码健壮性和可维护性。
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