android– 仅通过当前数据使用MediatorLiveData的最佳实践

概述将MediatorLiveData与多个源一起使用的最佳做法是什么？我在ViewModel中有一个MediatorLiveData,可以从最终显示的数据视图中访问.MediatorLiveData依赖于多个其他LiveDatas.其中一些来自存储库层,其中一些必须在ViewModel中处理,然后才能从MediatorLiveData访问它们,其中一些来自V

将MediatorliveData与多个源一起使用的最佳做法是什么？

我在viewmodel中有一个MediatorliveData,可以从最终显示的数据视图中访问.

MediatorliveData依赖于多个其他liveDatas.其中一些来自存储库层,其中一些必须在viewmodel中处理,然后才能从MediatorliveData访问它们,其中一些来自VIEw.

所以我当前的实现看起来像以下架构：

public Myviewmodel extends viewmodel {   liveData<Foo> liveData1;   liveData<bar> liveData2;   liveData<Foobar> liveData3;   //Some other liveDatas   MediatorliveData liveDataForVIEw   public Myviewmodel() {      liveDataForVIEw = new MediatorliveData();      //Do some preprocessing with some of the liveData      setupForVIEw();   }   public MediatorliveData getliveDataForVIEw() {      return liveDataForVIEw;   }   private voID setupForVIEw() {      liveDataForVIEw.addSource(liveData1, (foo -> {         if(liveData1.getValue() != null && liveData2.getValue() != null && liveData3.getValue() != null /*&& some other liveData-checks*/)            liveDataForVIEw.setValue(/*Some combinations of the liveDatas*/);      }));      //Add sources to the MediatorliveData for any other liveData   }}

通过这个实现我声明,输出liveData的值是在每个liveData出现后设置的.
在某些情况下,如果我留下一些空检查,我得到一个NullPointerException.
但是这个解决方案对我来说似乎有些混乱,因为对于我必须添加到viewmodel的每个liveData,我必须将它添加到每个源代码中.

解决方法:

首先你需要一些元组：

public class Tuple2<S, T> {    public final S first;    public final T second;    public Tuple2(S first, T second) {        this.first = first;        this.second = second;    }}

和

public class Tuple3<S, T, U> {    public final S first;    public final T second;    public final U third;    public Tuple3(S first, T second, U third) {        this.first = first;        this.second = second;        this.third = third;    }}

和

public class Tuple4<S, T, U, V> {    public final S first;    public final T second;    public final U third;    public final V fourth;    public Tuple4(S first, T second, U third, V fourth) {        this.first = first;        this.second = second;        this.third = third;        this.fourth = fourth;    }}

一旦你有了元组,就可以编写类似于transformations.map的辅助函数,除非你现在可以这样做：

public class liveDatatransformations {    private liveDatatransformations() {}    public static <S, T> liveData<Tuple2<S,T>> ifNotNull(liveData<S> first, liveData<T> second) {        MediatorliveData<Tuple2<S, T>> mediator = new MediatorliveData<>();        mediator.addSource(first, (_first) -> {            T _second = second.getValue();            if(_first != null && _second != null) {                mediator.setValue(new Tuple2(_first, _second));            }        });        mediator.addSource(second, (_second) -> {            S _first = first.getValue();            if(_first != null && _second != null) {                mediator.setValue(new Tuple2(_first, _second));            }        });        return mediator;    }    public static <S, T, U> liveData<Tuple3<S,T,U>> ifNotNull(liveData<S> first, liveData<T> second, liveData<U> third) {        MediatorliveData<Tuple3<S, T, U>> mediator = new MediatorliveData<>();        mediator.addSource(first, (_first) -> {            T _second = second.getValue();            U _third = third.getValue();            if(_first != null && _second != null && _third != null) {                mediator.setValue(new Tuple3(_first, _second, _third));            }        });        mediator.addSource(second, (_second) -> {            S _first = first.getValue();            U _third = third.getValue();            if(_first != null && _second != null && _third != null) {                mediator.setValue(new Tuple3(_first, _second, _third));            }        });        mediator.addSource(third, (_third) -> {            S _first = first.getValue();            T _second = second.getValue();            if(_first != null && _second != null && _third != null) {                mediator.setValue(new Tuple3(_first, _second, _third));            }        });        return mediator;    }    public static <S, T, U, V> liveData<Tuple4<S,T,U, V>> ifNotNull(liveData<S> first, liveData<T> second, liveData<U> third, liveData<V> fourth) {        MediatorliveData<Tuple4<S, T, U, V>> mediator = new MediatorliveData<>();        mediator.addSource(first, (_first) -> {            T _second = second.getValue();            U _third = third.getValue();            V _fourth = fourth.getValue();            if(_first != null && _second != null && _third != null && _fourth != null) {                mediator.setValue(new Tuple4(_first, _second, _third, _fourth));            }        });        mediator.addSource(second, (_second) -> {            S _first = first.getValue();            U _third = third.getValue();            V _fourth = fourth.getValue();            if(_first != null && _second != null && _third != null && _fourth != null) {                mediator.setValue(new Tuple4(_first, _second, _third, _fourth));            }        });        mediator.addSource(third, (_third) -> {            S _first = first.getValue();            T _second = second.getValue();            V _fourth = fourth.getValue();            if(_first != null && _second != null && _third != null && _fourth != null) {                mediator.setValue(new Tuple4(_first, _second, _third, _fourth));            }        });        mediator.addSource(fourth, (_fourth) -> {            S _first = first.getValue();            T _second = second.getValue();            U _third = third.getValue();            if(_first != null && _second != null && _third != null && _fourth != null) {                mediator.setValue(new Tuple4(_first, _second, _third, _fourth));            }        });        return mediator;    }}

现在你可以做到

liveData<???> liveDataForVIEw;private voID setupForVIEw() {   liveData<Tuple3<Foo, bar, Foobar>> intermediate =  liveDatatransformations.ifNotNull(liveData1, liveData2, liveData3);   liveDataForVIEw = transformations.map(intermediate, (tuple) -> {       Foo foo = tuple.first;       bar bar = tuple.second;       Foobar foobar = tuple.third;       return /*Some combinations of the liveDatas*/   });}

总结

以上是内存溢出为你收集整理的android – 仅通过当前数据使用MediatorLiveData的最佳实践全部内容，希望文章能够帮你解决android – 仅通过当前数据使用MediatorLiveData的最佳实践所遇到的程序开发问题。

如果觉得内存溢出网站内容还不错，欢迎将内存溢出网站推荐给程序员好友。