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https://github.com/M66B/FairEmail.git
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Added lifecycle-livedata inline
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M66B
194
app/src/main/java/androidx/lifecycle/Transformations.java
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194
app/src/main/java/androidx/lifecycle/Transformations.java
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/*
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* Copyright (C) 2017 The Android Open Source Project
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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package androidx.lifecycle;
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import androidx.annotation.MainThread;
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import androidx.annotation.NonNull;
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import androidx.annotation.Nullable;
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import androidx.arch.core.util.Function;
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/**
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* Transformation methods for {@link LiveData}.
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* <p>
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* These methods permit functional composition and delegation of {@link LiveData} instances. The
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* transformations are calculated lazily, and will run only when the returned {@link LiveData} is
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* observed. Lifecycle behavior is propagated from the input {@code source} {@link LiveData} to the
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* returned one.
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*/
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@SuppressWarnings("WeakerAccess")
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public class Transformations {
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private Transformations() {
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}
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/**
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* Returns a {@code LiveData} mapped from the input {@code source} {@code LiveData} by applying
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* {@code mapFunction} to each value set on {@code source}.
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* <p>
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* This method is analogous to {@link io.reactivex.Observable#map}.
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* <p>
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* {@code transform} will be executed on the main thread.
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* <p>
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* Here is an example mapping a simple {@code User} struct in a {@code LiveData} to a
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* {@code LiveData} containing their full name as a {@code String}.
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*
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* <pre>
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* LiveData<User> userLiveData = ...;
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* LiveData<String> userFullNameLiveData =
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* Transformations.map(
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* userLiveData,
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* user -> user.firstName + user.lastName);
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* });
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* </pre>
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*
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* @param source the {@code LiveData} to map from
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* @param mapFunction a function to apply to each value set on {@code source} in order to set
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* it
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* on the output {@code LiveData}
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* @param <X> the generic type parameter of {@code source}
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* @param <Y> the generic type parameter of the returned {@code LiveData}
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* @return a LiveData mapped from {@code source} to type {@code <Y>} by applying
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* {@code mapFunction} to each value set.
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*/
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@MainThread
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@NonNull
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public static <X, Y> LiveData<Y> map(
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@NonNull LiveData<X> source,
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@NonNull final Function<X, Y> mapFunction) {
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final MediatorLiveData<Y> result = new MediatorLiveData<>();
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result.addSource(source, new Observer<X>() {
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@Override
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public void onChanged(@Nullable X x) {
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result.setValue(mapFunction.apply(x));
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}
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});
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return result;
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}
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/**
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* Returns a {@code LiveData} mapped from the input {@code source} {@code LiveData} by applying
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* {@code switchMapFunction} to each value set on {@code source}.
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* <p>
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* The returned {@code LiveData} delegates to the most recent {@code LiveData} created by
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* calling {@code switchMapFunction} with the most recent value set to {@code source}, without
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* changing the reference. In this way, {@code switchMapFunction} can change the 'backing'
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* {@code LiveData} transparently to any observer registered to the {@code LiveData} returned
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* by {@code switchMap()}.
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* <p>
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* Note that when the backing {@code LiveData} is switched, no further values from the older
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* {@code LiveData} will be set to the output {@code LiveData}. In this way, the method is
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* analogous to {@link io.reactivex.Observable#switchMap}.
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* <p>
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* {@code switchMapFunction} will be executed on the main thread.
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* <p>
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* Here is an example class that holds a typed-in name of a user
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* {@code String} (such as from an {@code EditText}) in a {@link MutableLiveData} and
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* returns a {@code LiveData} containing a List of {@code User} objects for users that have
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* that name. It populates that {@code LiveData} by requerying a repository-pattern object
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* each time the typed name changes.
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* <p>
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* This {@code ViewModel} would permit the observing UI to update "live" as the user ID text
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* changes.
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*
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* <pre>
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* class UserViewModel extends AndroidViewModel {
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* MutableLiveData<String> nameQueryLiveData = ...
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*
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* LiveData<List<String>> getUsersWithNameLiveData() {
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* return Transformations.switchMap(
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* nameQueryLiveData,
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* name -> myDataSource.getUsersWithNameLiveData(name));
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* }
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*
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* void setNameQuery(String name) {
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* this.nameQueryLiveData.setValue(name);
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* }
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* }
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* </pre>
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*
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* @param source the {@code LiveData} to map from
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* @param switchMapFunction a function to apply to each value set on {@code source} to create a
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* new delegate {@code LiveData} for the returned one
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* @param <X> the generic type parameter of {@code source}
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* @param <Y> the generic type parameter of the returned {@code LiveData}
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* @return a LiveData mapped from {@code source} to type {@code <Y>} by delegating
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* to the LiveData returned by applying {@code switchMapFunction} to each
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* value set
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*/
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@MainThread
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@NonNull
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public static <X, Y> LiveData<Y> switchMap(
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@NonNull LiveData<X> source,
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@NonNull final Function<X, LiveData<Y>> switchMapFunction) {
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final MediatorLiveData<Y> result = new MediatorLiveData<>();
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result.addSource(source, new Observer<X>() {
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LiveData<Y> mSource;
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@Override
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public void onChanged(@Nullable X x) {
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LiveData<Y> newLiveData = switchMapFunction.apply(x);
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if (mSource == newLiveData) {
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return;
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}
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if (mSource != null) {
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result.removeSource(mSource);
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}
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mSource = newLiveData;
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if (mSource != null) {
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result.addSource(mSource, new Observer<Y>() {
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@Override
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public void onChanged(@Nullable Y y) {
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result.setValue(y);
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}
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});
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}
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}
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});
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return result;
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}
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/**
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* Creates a new {@link LiveData} object that does not emit a value until the source LiveData
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* value has been changed. The value is considered changed if {@code equals()} yields
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* {@code false}.
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*
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* @param source the input {@link LiveData}
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* @param <X> the generic type parameter of {@code source}
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* @return a new {@link LiveData} of type {@code X}
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*/
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@MainThread
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@NonNull
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public static <X> LiveData<X> distinctUntilChanged(@NonNull LiveData<X> source) {
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final MediatorLiveData<X> outputLiveData = new MediatorLiveData<>();
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outputLiveData.addSource(source, new Observer<X>() {
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boolean mFirstTime = true;
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@Override
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public void onChanged(X currentValue) {
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final X previousValue = outputLiveData.getValue();
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if (mFirstTime
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|| (previousValue == null && currentValue != null)
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|| (previousValue != null && !previousValue.equals(currentValue))) {
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mFirstTime = false;
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outputLiveData.setValue(currentValue);
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}
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}
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});
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return outputLiveData;
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}
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}
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