74 lines
2.3 KiB
Java
74 lines
2.3 KiB
Java
/*
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* Copyright 2017 Google Inc.
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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 org.thoughtcrime.securesms.util;
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import androidx.lifecycle.LifecycleOwner;
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import androidx.lifecycle.MutableLiveData;
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import androidx.lifecycle.Observer;
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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 org.thoughtcrime.securesms.logging.Log;
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import java.util.concurrent.atomic.AtomicBoolean;
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/**
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* A lifecycle-aware observable that sends only new updates after subscription, used for events like
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* navigation and Snackbar messages.
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* <p>
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* This avoids a common problem with events: on configuration change (like rotation) an update
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* can be emitted if the observer is active. This LiveData only calls the observable if there's an
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* explicit call to setValue() or call().
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* <p>
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* Note that only one observer is going to be notified of changes.
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*/
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public class SingleLiveEvent<T> extends MutableLiveData<T> {
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private static final String TAG = SingleLiveEvent.class.getSimpleName();
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private final AtomicBoolean mPending = new AtomicBoolean(false);
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@MainThread
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public void observe(@NonNull LifecycleOwner owner, @NonNull final Observer<? super T> observer) {
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if (hasActiveObservers()) {
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Log.w(TAG, "Multiple observers registered but only one will be notified of changes.");
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}
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// Observe the internal MutableLiveData
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super.observe(owner, t -> {
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if (mPending.compareAndSet(true, false)) {
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observer.onChanged(t);
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}
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});
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}
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@MainThread
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public void setValue(@Nullable T t) {
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mPending.set(true);
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super.setValue(t);
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}
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/**
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* Used for cases where T is Void, to make calls cleaner.
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*/
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@MainThread
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public void call() {
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setValue(null);
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}
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}
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