design/src/android/support/design/widget/ViewOffsetHelper.java

/*
 * Copyright (C) 2015 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 android.support.design.widget;

import android.os.Build;
import android.support.v4.view.ViewCompat;
import android.view.View;
import android.view.ViewParent;

/**
 * Utility helper for moving a {@link android.view.View} around using
 * {@link android.view.View#offsetLeftAndRight(int)} and
 * {@link android.view.View#offsetTopAndBottom(int)}.
 * <p>
 * Also the setting of absolute offsets (similar to translationX/Y), rather than additive
 * offsets.
 */
class ViewOffsetHelper {

    private final View mView;

    private int mLayoutTop;
    private int mLayoutLeft;
    private int mOffsetTop;
    private int mOffsetLeft;

    public ViewOffsetHelper(View view) {
        mView = view;
    }

    public void onViewLayout() {
        // Now grab the intended top
        mLayoutTop = mView.getTop();
        mLayoutLeft = mView.getLeft();

        // And offset it as needed
        updateOffsets();
    }

    private void updateOffsets() {
        ViewCompat.offsetTopAndBottom(mView, mOffsetTop - (mView.getTop() - mLayoutTop));
        ViewCompat.offsetLeftAndRight(mView, mOffsetLeft - (mView.getLeft() - mLayoutLeft));

        // Manually invalidate the view and parent to make sure we get drawn pre-M
        if (Build.VERSION.SDK_INT < 23) {
            tickleInvalidationFlag(mView);
            final ViewParent vp = mView.getParent();
            if (vp instanceof View) {
                tickleInvalidationFlag((View) vp);
            }
        }
    }

    private static void tickleInvalidationFlag(View view) {
        final float x = ViewCompat.getTranslationX(view);
        ViewCompat.setTranslationY(view, x + 1);
        ViewCompat.setTranslationY(view, x);
    }

    /**
     * Set the top and bottom offset for this {@link ViewOffsetHelper}'s view.
     *
     * @param offset the offset in px.
     * @return true if the offset has changed
     */
    public boolean setTopAndBottomOffset(int offset) {
        if (mOffsetTop != offset) {
            mOffsetTop = offset;
            updateOffsets();
            return true;
        }
        return false;
    }

    /**
     * Set the left and right offset for this {@link ViewOffsetHelper}'s view.
     *
     * @param offset the offset in px.
     * @return true if the offset has changed
     */
    public boolean setLeftAndRightOffset(int offset) {
        if (mOffsetLeft != offset) {
            mOffsetLeft = offset;
            updateOffsets();
            return true;
        }
        return false;
    }

    public int getTopAndBottomOffset() {
        return mOffsetTop;
    }

    public int getLeftAndRightOffset() {
        return mOffsetLeft;
    }
}