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AutoClearedValue.java

/*
 * Copyright (C) 2017 The Android Open Source Project
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.android.example.github.util;

import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;

/**
 * A value holder that automatically clears the reference if the Fragment's view is destroyed.
 * @param <T>
 */
public class AutoClearedValue<T> {
    private T value;
    public AutoClearedValue(Fragment fragment, T value) {
        FragmentManager fragmentManager = fragment.getFragmentManager();
        fragmentManager.registerFragmentLifecycleCallbacks(
                new FragmentManager.FragmentLifecycleCallbacks() {
                    @Override
                    public void onFragmentViewDestroyed(FragmentManager fm, Fragment f) {
                        if (f == fragment) {
                            AutoClearedValue.this.value = null;
                            fragmentManager.unregisterFragmentLifecycleCallbacks(this);
                        }
                    }
                },false);
        this.value = value;
    }

public T get() {
        return value;
    }
}