com.google.gapid.widgets.VisibilityTrackingTreeViewer.java Source code

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Here is the source code for com.google.gapid.widgets.VisibilityTrackingTreeViewer.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.widgets;

import com.google.common.collect.Lists;
import com.google.gapid.util.Trees;

import org.eclipse.jface.viewers.IBaseLabelProvider;
import org.eclipse.jface.viewers.IContentProvider;
import org.eclipse.jface.viewers.TreeViewer;
import org.eclipse.swt.widgets.Tree;
import org.eclipse.swt.widgets.TreeItem;

import java.util.Collections;
import java.util.List;
import java.util.Set;

/**
 * A {@link TreeViewer} that notifies the bound {@link IContentProvider} and
 * {@link IBaseLabelProvider} of visibility changes if they also implement
 * the {@link Listener} interface.
 */
public class VisibilityTrackingTreeViewer extends TreeViewer {
    private Set<TreeItem> visible = Collections.emptySet();
    private Listener[] listeners;

    public VisibilityTrackingTreeViewer(Tree tree) {
        super(tree);
        updateListeners();
        tree.addPaintListener(e -> updateVisibility());
    }

    private void updateVisibility() {
        if (listeners == null) {
            return;
        }

        Set<TreeItem> seen = Trees.getVisibleItems(getTree());
        if (seen == null) {
            return; // No reliable data.
        }
        for (TreeItem item : visible) {
            if (!seen.contains(item) && !item.isDisposed()) {
                for (Listener listener : listeners) {
                    listener.onHide(item);
                }
            }
        }
        for (TreeItem item : seen) {
            if (!visible.contains(item)) {
                for (Listener listener : listeners) {
                    listener.onShow(item);
                }
            }
        }
        visible = seen;
    }

    @Override
    protected void inputChanged(Object input, Object oldInput) {
        // Cause all visible items to receive a show event.
        visible = Collections.emptySet();
        super.inputChanged(input, oldInput);
    }

    @Override
    public void setLabelProvider(IBaseLabelProvider labelProvider) {
        super.setLabelProvider(labelProvider);
        updateListeners();
    }

    @Override
    public void setContentProvider(IContentProvider provider) {
        super.setContentProvider(provider);
        updateListeners();
    }

    private void updateListeners() {
        List<Listener> found = Lists.newArrayList();
        IContentProvider contentProvider = getContentProvider();
        if (contentProvider instanceof Listener) {
            found.add((Listener) contentProvider);
        }

        IBaseLabelProvider labelProvider = getLabelProvider();
        if (labelProvider instanceof Listener) {
            found.add((Listener) labelProvider);
        }

        listeners = found.isEmpty() ? null : found.toArray(new Listener[found.size()]);
    }

    /**
     * The interface the {@link IContentProvider} and {@link IBaseLabelProvider} can
     * implement to be notified about {@link TreeItem TreeItems} being made visible
     * and hidden usually by scrolling.
     */
    public static interface Listener {
        /**
         * @param item the item that has been made visible.
         */
        public default void onShow(TreeItem item) {
            /* empty */ }

        /**
         * @param item the item that has been made invisible.
         */
        public default void onHide(TreeItem item) {
            /* empty */ }
    }
}