android - 如何从 MutableLiveData 发出不同的值？

Question

我观察到 MutableLiveData 会触发观察者的 onChanged，即使向其 setValue 方法提供相同的对象实例也是如此。

//Fragment#onCreateView - scenario1
val newValue = "newValue"
mutableLiveData.setValue(newValue) //triggers observer
mutableLiveData.setValue(newValue) //triggers observer

//Fragment#onCreateView - scenario2
val newValue = "newValue"
mutableLiveData.postValue(newValue) //triggers observer
mutableLiveData.postValue(newValue) //does not trigger observer

如果向 setValue()/postValue() 提供相同或等效的实例，是否有办法避免观察者被通知两次

我尝试扩展 MutableLiveData 但那没有用。我可能在这里遗漏了一些东西

class DistinctLiveData<T> : MutableLiveData<T>() {

    private var cached: T? = null

    @Synchronized override fun setValue(value: T) {
        if(value != cached) {
            cached = value
            super.setValue(value)
        }
    }

    @Synchronized override fun postValue(value: T) {
        if(value != cached) {
            cached = value
            super.postValue(value)
        }
    }
}

Answer 1

API 中已有:Transformations.distinctUntilChanged()

distinctUntilChanged

public static LiveData<X> distinctUntilChanged (LiveData<X> source)

Creates a new LiveData object does not emit a value until the source LiveData value has been changed. The value is considered changed if equals() yields false.

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