com.google.gapid.util.SelectionHandler.java Source code

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Here is the source code for com.google.gapid.util.SelectionHandler.java

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/*
 * Copyright (C) 2017 Google Inc.
 *
 * 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.google.gapid.util;

import static com.google.gapid.widgets.Widgets.scheduleIfNotDisposed;

import com.google.common.util.concurrent.Futures;
import com.google.common.util.concurrent.ListenableFuture;

import org.eclipse.swt.SWT;
import org.eclipse.swt.widgets.Event;
import org.eclipse.swt.widgets.Widget;

import java.util.concurrent.Callable;
import java.util.concurrent.Future;
import java.util.concurrent.atomic.AtomicInteger;
import java.util.function.Consumer;
import java.util.logging.Logger;

/**
 * Helper class to manage user selection and model selection events.
 */
public abstract class SelectionHandler<W extends Widget> {
    private final Logger log;
    protected final W widget;
    private final AtomicInteger lastSelectionEventId = new AtomicInteger();
    private boolean handlingUiSelection;
    private Future<?> lastSelectionFuture = Futures.immediateFuture(null);

    public SelectionHandler(Logger log, W widget) {
        this.log = log;
        this.widget = widget;

        widget.addListener(SWT.Selection, e -> updateSelectionFromUi(e));
    }

    private void updateSelectionFromUi(Event e) {
        handlingUiSelection = true;
        try {
            updateModel(e);
        } finally {
            handlingUiSelection = false;
        }
    }

    public <T> void updateSelectionFromModel(Callable<T> onBgThread, Consumer<T> onUiThread) {
        if (handlingUiSelection) {
            return;
        }

        int currentSelection = lastSelectionEventId.incrementAndGet();
        lastSelectionFuture.cancel(true);
        ListenableFuture<T> future = Scheduler.EXECUTOR.submit(onBgThread);
        lastSelectionFuture = future;

        Futures.addCallback(future, new LoggingCallback<T>(log) {
            @Override
            public void onSuccess(T result) {
                if (result != null && isCurrentSelection(currentSelection)) {
                    scheduleIfNotDisposed(widget, () -> {
                        if (isCurrentSelection(currentSelection)) {
                            onUiThread.accept(result);
                        }
                    });
                }
            }
        });
    }

    protected boolean isCurrentSelection(int selection) {
        return lastSelectionEventId.get() == selection;
    }

    protected abstract void updateModel(Event e);
}