android/sdk/src/main/java/org/apache/weex/ui/component/list/WXPagerSnapHelper.java

/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you 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 org.apache.weex.ui.component.list;

import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.support.v7.widget.OrientationHelper;
import android.support.v7.widget.PagerSnapHelper;
import android.support.v7.widget.RecyclerView;
import android.view.View;

public class WXPagerSnapHelper extends PagerSnapHelper {
    @Nullable
    private OrientationHelper mVerticalHelper;
    @Nullable
    private OrientationHelper mHorizontalHelper;

    @Nullable
    @Override
    public int[] calculateDistanceToFinalSnap(@NonNull RecyclerView.LayoutManager layoutManager, @NonNull View targetView) {

        int[] out = new int[2];
        if (layoutManager.canScrollHorizontally()) {
            out[0] = this.distanceToStart(layoutManager, targetView, this.getHorizontalHelper(layoutManager));
        } else {
            out[0] = 0;
        }

        if (layoutManager.canScrollVertically()) {
            out[1] = this.distanceToStart(layoutManager, targetView, this.getVerticalHelper(layoutManager));
        } else {
            out[1] = 0;
        }

        return out;
    }

    @NonNull
    private OrientationHelper getVerticalHelper(@NonNull RecyclerView.LayoutManager layoutManager) {
        if (this.mVerticalHelper == null) {
            this.mVerticalHelper = OrientationHelper.createVerticalHelper(layoutManager);
        }

        return this.mVerticalHelper;
    }

    @NonNull
    private OrientationHelper getHorizontalHelper(@NonNull RecyclerView.LayoutManager layoutManager) {
        if (this.mHorizontalHelper == null) {
            this.mHorizontalHelper = OrientationHelper.createHorizontalHelper(layoutManager);
        }

        return this.mHorizontalHelper;
    }

    private int distanceToStart(@NonNull RecyclerView.LayoutManager layoutManager, @NonNull View targetView, OrientationHelper helper) {
        return helper.getDecoratedStart(targetView) - helper.getStartAfterPadding();
    }
}