v4/widget/SwipeRefreshLayout.java

/*
 * Copyright (C) 2013 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.v4.widget;

import android.content.Context;
import android.content.res.Resources;
import android.content.res.TypedArray;
import android.support.v4.view.MotionEventCompat;
import android.support.v4.view.ViewCompat;
import android.util.AttributeSet;
import android.util.DisplayMetrics;
import android.util.Log;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewConfiguration;
import android.view.ViewGroup;
import android.view.animation.Animation;
import android.view.animation.Animation.AnimationListener;
import android.view.animation.DecelerateInterpolator;
import android.view.animation.Transformation;
import android.widget.AbsListView;

/**
 * The SwipeRefreshLayout should be used whenever the user can refresh the
 * contents of a view via a vertical swipe gesture. The activity that
 * instantiates this view should add an OnRefreshListener to be notified
 * whenever the swipe to refresh gesture is completed. The SwipeRefreshLayout
 * will notify the listener each and every time the gesture is completed again;
 * the listener is responsible for correctly determining when to actually
 * initiate a refresh of its content. If the listener determines there should
 * not be a refresh, it must call setRefreshing(false) to cancel any visual
 * indication of a refresh. If an activity wishes to show just the progress
 * animation, it should call setRefreshing(true). To disable the gesture and
 * progress animation, call setEnabled(false) on the view.
 * <p>
 * This layout should be made the parent of the view that will be refreshed as a
 * result of the gesture and can only support one direct child. This view will
 * also be made the target of the gesture and will be forced to match both the
 * width and the height supplied in this layout. The SwipeRefreshLayout does not
 * provide accessibility events; instead, a menu item must be provided to allow
 * refresh of the content wherever this gesture is used.
 * </p>
 */
public class SwipeRefreshLayout extends ViewGroup {
    // Maps to ProgressBar.Large style
    public static final int LARGE = MaterialProgressDrawable.LARGE;
    // Maps to ProgressBar default style
    public static final int DEFAULT = MaterialProgressDrawable.DEFAULT;
    // Maps to ProgressBar.Small style
    public static final int SMALL = MaterialProgressDrawable.SMALL;

    private static final String LOG_TAG = SwipeRefreshLayout.class.getSimpleName();

    private static final int MAX_ALPHA = 255;

    private static final int CIRCLE_DIAMETER = 40;
    private static final int CIRCLE_DIAMETER_LARGE = 96;
    private static final int CIRCLE_DIAMETER_SMALL = 16;

    private static final float DECELERATE_INTERPOLATION_FACTOR = 2f;
    private static final int INVALID_POINTER = -1;
    private static final float DRAG_RATE = .5f;
    private static final int MAX_OVERSWIPE = 80;

    // Default background for the progress spinner
    private static final int CIRCLE_BG_LIGHT = 0xFFFAFAFA;
    private static final float MIN_CIRCLE_SCALE = .1f;
    // Default offset in dips from the top of the view to where the progress spinner should stop
    private static final int DEFAULT_CIRCLE_TARGET = 64;

    private View mTarget; // the target of the gesture
    private OnRefreshListener mListener;
    private boolean mRefreshing = false;
    private int mTouchSlop;
    private float mDistanceToTriggerSync = -1;
    private int mMediumAnimationDuration;
    private int mShortAnimationDuration;
    private int mCurrentTargetOffsetTop;

    private float mInitialMotionY;
    private boolean mIsBeingDragged;
    private int mActivePointerId = INVALID_POINTER;
    // Whether this item is scaled up rather than clipped
    private boolean mScale;

    // Target is returning to its start offset because it was cancelled or a
    // refresh was triggered.
    private boolean mReturningToStart;
    private final DecelerateInterpolator mDecelerateInterpolator;
    private static final int[] LAYOUT_ATTRS = new int[] {
        android.R.attr.enabled
    };

    private CircleImageView mCircleView;

    protected int mFrom;

    protected int mOriginalOffsetTop;

    private MaterialProgressDrawable mProgress;

    private Animation mScaleAnimation;

    private Animation mScaleDownAnimation;

    private float mLastY;

    private float mTargetCirclePosition;

    private boolean mNotify;

    private int mCircleWidth;

    private int mCircleHeight;

    private Animation.AnimationListener mRefreshListener = new Animation.AnimationListener() {
        @Override
        public void onAnimationStart(Animation animation) {
        }

        @Override
        public void onAnimationRepeat(Animation animation) {
        }

        @Override
        public void onAnimationEnd(Animation animation) {
            if (mRefreshing) {
                mProgress.showArrow(false);
                mProgress.start();
                if (mNotify) {
                    if (mListener != null) {
                        mListener.onRefresh();
                    }
                }
            } else {
                mProgress.stop();
                mCircleView.setVisibility(View.GONE);
                // Return the circle to its start position
                if (mScale) {
                    setAnimationProgress(0 /* animation complete and view is hidden */);
                } else {
                    setAnimationProgress(1 /* animation complete and view is showing */);
                    setTargetOffsetTopAndBottom(-mCircleHeight - mCurrentTargetOffsetTop,
                            true /* requires update */);
                    mCircleView.setVisibility(View.VISIBLE);
                }
            }
            mCurrentTargetOffsetTop = mCircleView.getTop();
        }
    };

    private void setColorViewAlpha(int targetAlpha) {
        mCircleView.getBackground().setAlpha(targetAlpha);
        mProgress.setAlpha(targetAlpha);
    }

    /**
     * The refresh indicator starting and resting position is always positioned
     * near the top of the refreshing content. This position is a consistent
     * location, but can be adjusted in either direction based on whether or not
     * there is a toolbar or actionbar present.
     *
     * @param scale Set to true if there is no view at a higher z-order than
     *            where the progress spinner is set to appear.
     * @param start The offset in pixels from the top of this view at which the
     *            progress spinner should appear.
     * @param end The offset in pixels from the top of this view at which the
     *            progress spinner should come to rest after a successful swipe
     *            gesture.
     */
    public void setProgressViewOffset(boolean scale, int start, int end) {
        mScale = scale;
        mCircleView.setVisibility(View.GONE);
        mOriginalOffsetTop = mCurrentTargetOffsetTop = start;
        mDistanceToTriggerSync = (mTargetCirclePosition / DRAG_RATE);
        mTargetCirclePosition = end;
        mCircleView.invalidate();
    }

    /**
     * One of SMALL, DEFAULT, or LARGE. DEFAULT is ProgressBar default styling.
     */
    public void setSize(int size) {
        if (size != MaterialProgressDrawable.LARGE && size != MaterialProgressDrawable.DEFAULT
                && size != MaterialProgressDrawable.SMALL) {
            return;
        }
        final DisplayMetrics metrics = getResources().getDisplayMetrics();
        if (size == MaterialProgressDrawable.LARGE) {
            mCircleHeight = mCircleWidth = (int) (CIRCLE_DIAMETER_LARGE * metrics.density);
        } else if (size == MaterialProgressDrawable.SMALL) {
            mCircleHeight = mCircleWidth = (int) (CIRCLE_DIAMETER_SMALL * metrics.density);
        } else {
            mCircleHeight = mCircleWidth = (int) (CIRCLE_DIAMETER * metrics.density);
        }
        mProgress.updateSizes(size);
    }

    /**
     * Simple constructor to use when creating a SwipeRefreshLayout from code.
     *
     * @param context
     */
    public SwipeRefreshLayout(Context context) {
        this(context, null);
    }

    /**
     * Constructor that is called when inflating SwipeRefreshLayout from XML.
     *
     * @param context
     * @param attrs
     */
    public SwipeRefreshLayout(Context context, AttributeSet attrs) {
        super(context, attrs);

        mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();

        mMediumAnimationDuration = getResources().getInteger(
                android.R.integer.config_mediumAnimTime);
        mShortAnimationDuration = getResources().getInteger(
                android.R.integer.config_shortAnimTime);

        setWillNotDraw(false);
        mDecelerateInterpolator = new DecelerateInterpolator(DECELERATE_INTERPOLATION_FACTOR);

        final TypedArray a = context.obtainStyledAttributes(attrs, LAYOUT_ATTRS);
        setEnabled(a.getBoolean(0, true));
        a.recycle();

        final DisplayMetrics metrics = getResources().getDisplayMetrics();
        mCircleWidth = (int) (CIRCLE_DIAMETER * metrics.density);
        mCircleHeight = (int) (CIRCLE_DIAMETER * metrics.density);

        mTargetCirclePosition = DEFAULT_CIRCLE_TARGET * metrics.density;
        // Since the circle moves at 1/2 rate of drag, and we want the circle to
        // end at 64, and its starts -Diameter offscreen, it needs to move overall this
        mDistanceToTriggerSync = (mTargetCirclePosition / DRAG_RATE)
                + (mCircleWidth / DRAG_RATE);
        createProgressView();
        ViewCompat.setChildrenDrawingOrderEnabled(this, true);
    }

    protected int getChildDrawingOrder (int childCount, int i) {
        if (getChildAt(i).equals(mCircleView)) {
            return childCount - 1;
        }
        return i;
    }

    private void createProgressView() {
        mCircleView = new CircleImageView(getContext(), CIRCLE_BG_LIGHT, CIRCLE_DIAMETER/2);
        mProgress = new MaterialProgressDrawable(getContext(), this);
        mCircleView.setImageDrawable(mProgress);
        addView(mCircleView);
        mCurrentTargetOffsetTop = mOriginalOffsetTop = -mCircleWidth;
    }

    /**
     * Set the listener to be notified when a refresh is triggered via the swipe
     * gesture.
     */
    public void setOnRefreshListener(OnRefreshListener listener) {
        mListener = listener;
    }

    /**
     * Notify the widget that refresh state has changed. Do not call this when
     * refresh is triggered by a swipe gesture.
     *
     * @param refreshing Whether or not the view should show refresh progress.
     */
    public void setRefreshing(boolean refreshing) {
        if (refreshing && mRefreshing != refreshing) {
            // scale and show
            mRefreshing = refreshing;
            setTargetOffsetTopAndBottom((int) (mTargetCirclePosition - mCircleView.getTop()),
                    true /* requires update */);
            mNotify = false;
            startScaleUpAnimation(mRefreshListener);
        } else {
            setRefreshing(refreshing, false /* notify */);
        }
    }

    private void startScaleUpAnimation(AnimationListener listener) {
        mCircleView.setVisibility(View.VISIBLE);
        mScaleAnimation = new Animation() {
            @Override
            public void applyTransformation(float interpolatedTime, Transformation t) {
                setAnimationProgress(interpolatedTime);
            }
        };
        mScaleAnimation.setDuration(mMediumAnimationDuration);
        if (listener != null) {
            mCircleView.setAnimationListener(listener);
        }
        mCircleView.clearAnimation();
        mCircleView.startAnimation(mScaleAnimation);
    }

    /**
     * Pre API 11, this does an alpha animation.
     * @param progress
     */
    private void setAnimationProgress(float progress) {
        if (android.os.Build.VERSION.SDK_INT < 11) {
            setColorViewAlpha((int) (progress * MAX_ALPHA));
        } else {
            ViewCompat.setScaleX(mCircleView, progress);
            ViewCompat.setScaleY(mCircleView, progress);
        }
    }

    private void setRefreshing(boolean refreshing, final boolean notify) {
        if (mRefreshing != refreshing) {
            mNotify = notify;
            ensureTarget();
            mRefreshing = refreshing;
            if (mRefreshing) {
                animateOffsetToCorrectPosition(mCurrentTargetOffsetTop, mRefreshListener);
            } else {
                startScaleDownAnimation(mRefreshListener);
            }
        }
    }

    private void startScaleDownAnimation(Animation.AnimationListener listener) {
        mScaleDownAnimation = new Animation() {
            @Override
            public void applyTransformation(float interpolatedTime, Transformation t) {
                setAnimationProgress(1 - interpolatedTime);
            }
        };
        mScaleDownAnimation.setDuration(mShortAnimationDuration);
        if (listener != null) {
            mCircleView.setAnimationListener(listener);
        }
        mCircleView.clearAnimation();
        mCircleView.startAnimation(mScaleDownAnimation);
    }

    public void setProgressBackgroundColor(int colorRes) {
        mCircleView.setBackgroundColor(colorRes);
    }

    /**
     * @deprecated Use {@link #setColorSchemeResources(int...)}
     */
    @Deprecated
    public void setColorScheme(int... colors) {
        setColorSchemeResources(colors);
    }

    /**
     * Set the color resources used in the progress animation from color resources.
     * The first color will also be the color of the bar that grows in response
     * to a user swipe gesture.
     *
     * @param colorResIds
     */
    public void setColorSchemeResources(int... colorResIds) {
        final Resources res = getResources();
        int[] colorRes = new int[colorResIds.length];
        for (int i = 0; i < colorResIds.length; i++) {
            colorRes[i] = res.getColor(colorResIds[i]);
        }
        setColorSchemeColors(colorRes);
    }

    /**
     * Set the colors used in the progress animation. The first
     * color will also be the color of the bar that grows in response to a user
     * swipe gesture.
     *
     * @param colors
     */
    public void setColorSchemeColors(int... colors) {
        ensureTarget();
        mProgress.setColorSchemeColors(colors);
    }

    /**
     * @return Whether the SwipeRefreshWidget is actively showing refresh
     *         progress.
     */
    public boolean isRefreshing() {
        return mRefreshing;
    }

    private void ensureTarget() {
        // Don't bother getting the parent height if the parent hasn't been laid
        // out yet.
        if (mTarget == null) {
            for (int i = 0; i < getChildCount(); i++) {
                View child = getChildAt(i);
                if (!child.equals(mCircleView)) {
                    mTarget = child;
                    break;
                }
            }
        }
    }

    /**
     * Set the distance to trigger a sync in dips
     *
     * @param distance
     */
    public void setDistanceToTriggerSync(int distance) {
        mDistanceToTriggerSync = distance;
    }

    @Override
    protected void onLayout(boolean changed, int left, int top, int right, int bottom) {
        final int width = getMeasuredWidth();
        final int height = getMeasuredHeight();
        if (getChildCount() == 0) {
            return;
        }
        if (mTarget == null) {
            ensureTarget();
        }
        if (mTarget == null) {
            return;
        }
        final View child = mTarget;
        final int childLeft = getPaddingLeft();
        final int childTop = getPaddingTop();
        final int childWidth = width - getPaddingLeft() - getPaddingRight();
        final int childHeight = height - getPaddingTop() - getPaddingBottom();
        child.layout(childLeft, childTop, childLeft + childWidth, childTop + childHeight);
        mCircleView.layout((width / 2 - mCircleWidth / 2), mCurrentTargetOffsetTop,
                (width / 2 + mCircleWidth / 2), mCurrentTargetOffsetTop + mCircleHeight);
    }

    @Override
    public void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        if (mTarget == null) {
            ensureTarget();
        }
        if (mTarget == null) {
            return;
        }
        mTarget.measure(MeasureSpec.makeMeasureSpec(
                getMeasuredWidth() - getPaddingLeft() - getPaddingRight(),
                MeasureSpec.EXACTLY), MeasureSpec.makeMeasureSpec(
                getMeasuredHeight() - getPaddingTop() - getPaddingBottom(), MeasureSpec.EXACTLY));
        mCircleView.measure(MeasureSpec.makeMeasureSpec(mCircleWidth, MeasureSpec.EXACTLY),
                MeasureSpec.makeMeasureSpec(mCircleHeight, MeasureSpec.EXACTLY));
    }

    /**
     * @return Whether it is possible for the child view of this layout to
     *         scroll up. Override this if the child view is a custom view.
     */
    public boolean canChildScrollUp() {
        if (android.os.Build.VERSION.SDK_INT < 14) {
            if (mTarget instanceof AbsListView) {
                final AbsListView absListView = (AbsListView) mTarget;
                return absListView.getChildCount() > 0
                        && (absListView.getFirstVisiblePosition() > 0 || absListView.getChildAt(0)
                                .getTop() < absListView.getPaddingTop());
            } else {
                return mTarget.getScrollY() > 0;
            }
        } else {
            return ViewCompat.canScrollVertically(mTarget, -1);
        }
    }

    @Override
    public boolean onInterceptTouchEvent(MotionEvent ev) {
        ensureTarget();

        final int action = MotionEventCompat.getActionMasked(ev);

        if (mReturningToStart && action == MotionEvent.ACTION_DOWN) {
            mReturningToStart = false;
        }

        if (!isEnabled() || mReturningToStart || canChildScrollUp() || mRefreshing) {
            // Fail fast if we're not in a state where a swipe is possible
            return false;
        }

        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mLastY = mInitialMotionY = ev.getY();
                setTargetOffsetTopAndBottom(mOriginalOffsetTop - mCircleView.getTop(), true);
                mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
                mIsBeingDragged = false;
                break;

            case MotionEvent.ACTION_MOVE:
                if (mActivePointerId == INVALID_POINTER) {
                    Log.e(LOG_TAG, "Got ACTION_MOVE event but don't have an active pointer id.");
                    return false;
                }

                final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
                if (pointerIndex < 0) {
                    Log.e(LOG_TAG, "Got ACTION_MOVE event but have an invalid active pointer id.");
                    return false;
                }

                final float y = MotionEventCompat.getY(ev, pointerIndex);
                final float yDiff = y - mInitialMotionY;
                if (yDiff > mTouchSlop) {
                    mIsBeingDragged = true;
                }
                break;

            case MotionEventCompat.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                break;

            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                mIsBeingDragged = false;
                mActivePointerId = INVALID_POINTER;
                break;
        }

        return mIsBeingDragged;
    }

    @Override
    public void requestDisallowInterceptTouchEvent(boolean b) {
        // Nope.
    }

    @Override
    public boolean onTouchEvent(MotionEvent ev) {
        final int action = MotionEventCompat.getActionMasked(ev);

        if (mReturningToStart && action == MotionEvent.ACTION_DOWN) {
            mReturningToStart = false;
        }

        if (!isEnabled() || mReturningToStart || canChildScrollUp()) {
            // Fail fast if we're not in a state where a swipe is possible
            return false;
        }

        switch (action) {
            case MotionEvent.ACTION_DOWN:
                mLastY = mInitialMotionY = ev.getY();
                mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
                mIsBeingDragged = false;
                break;

            case MotionEvent.ACTION_MOVE:
                final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
                if (pointerIndex < 0) {
                    Log.e(LOG_TAG, "Got ACTION_MOVE event but have an invalid active pointer id.");
                    return false;
                }

                final float y = MotionEventCompat.getY(ev, pointerIndex);
                final float yDiff = y - mInitialMotionY;

                if (!mIsBeingDragged && yDiff > mTouchSlop) {
                    mIsBeingDragged = true;
                }

                if (mIsBeingDragged) {
                    // User velocity passed min velocity; trigger a refresh
                    if (yDiff > mDistanceToTriggerSync) {
                        // Continue updating circle, but at a reduced rate
                        float p = Math.max(0,
                                Math.min((yDiff - mDistanceToTriggerSync), MAX_OVERSWIPE)
                                        / MAX_OVERSWIPE / 2);
                        double q = (p - Math.pow(p, 2));
                        double extraDrag = (2 * MAX_OVERSWIPE * q);
                        if (mTargetCirclePosition + extraDrag
                                <= (mTargetCirclePosition + MAX_OVERSWIPE)) {
                            setTargetOffsetTopAndBottom(
                                    (int) (mTargetCirclePosition + extraDrag
                                            - mCurrentTargetOffsetTop),
                                    true /* requires update */);
                        }
                        if (mScale || mCurrentTargetOffsetTop > -mCircleHeight / 2) {
                            // start showing the arrow
                            float pullPercent = yDiff / mDistanceToTriggerSync * DRAG_RATE;
                            mProgress.setProgressRotation((float) (Math.PI / 4 * pullPercent));
                            mProgress.setArrowScale(1f);
                        }
                    } else {
                        if (mCircleView.getVisibility() != View.VISIBLE) {
                            mCircleView.setVisibility(View.VISIBLE);
                        }
                        mProgress.showArrow(true);
                        if (mScale) {
                            setAnimationProgress(yDiff / mDistanceToTriggerSync);
                        }
                        // Just track the user's movement
                        setTargetOffsetTopAndBottom((int) ((y - mLastY) * DRAG_RATE),
                                true /* requires update */);
                        if (mScale || mCurrentTargetOffsetTop > -mCircleHeight / 2) {
                            // start showing the arrow
                            float pullPercent = yDiff / mDistanceToTriggerSync;
                            float startTrim = (float) (.2 * Math.min(.75f, (pullPercent)));
                            mProgress.setStartEndTrim(startTrim,
                                    Math.min(.75f, pullPercent));
                            mProgress.setProgressRotation((float) (Math.PI / 4 * pullPercent));
                            mProgress.setArrowScale(Math.min(1f, pullPercent));
                        }
                    }
                }
                mLastY = y;
                break;

            case MotionEventCompat.ACTION_POINTER_DOWN: {
                final int index = MotionEventCompat.getActionIndex(ev);
                mActivePointerId = MotionEventCompat.getPointerId(ev, index);
                break;
            }

            case MotionEventCompat.ACTION_POINTER_UP:
                onSecondaryPointerUp(ev);
                break;

            case MotionEvent.ACTION_UP:
            case MotionEvent.ACTION_CANCEL:
                mIsBeingDragged = false;
                if (mCurrentTargetOffsetTop >= mTargetCirclePosition) {
                    setRefreshing(true, true /* notify */);
                    mProgress.showArrow(false);
                } else {
                    // cancel refresh
                    mRefreshing = false;
                    mProgress.setStartEndTrim(0f, 0f);
                    animateOffsetToStartPosition(mCurrentTargetOffsetTop, null);
                    mProgress.showArrow(false);
                }
                mActivePointerId = INVALID_POINTER;
                return false;
        }

        return true;
    }

    private void animateOffsetToCorrectPosition(int from, AnimationListener listener) {
        mFrom = from;
        mAnimateToCorrectPosition.reset();
        mAnimateToCorrectPosition.setDuration(mMediumAnimationDuration);
        mAnimateToCorrectPosition.setInterpolator(mDecelerateInterpolator);
        if (listener != null) {
            mCircleView.setAnimationListener(listener);
        }
        mCircleView.clearAnimation();
        mCircleView.startAnimation(mAnimateToCorrectPosition);
    }

    private void animateOffsetToStartPosition(int from, AnimationListener listener) {
        mFrom = from;
        mAnimateToStartPosition.reset();
        mAnimateToStartPosition.setDuration(mMediumAnimationDuration);
        mAnimateToStartPosition.setInterpolator(mDecelerateInterpolator);
        if (listener != null) {
            mCircleView.setAnimationListener(listener);
        }
        mCircleView.clearAnimation();
        mCircleView.startAnimation(mAnimateToStartPosition);
    }

    private final Animation mAnimateToCorrectPosition = new Animation() {
        @Override
        public void applyTransformation(float interpolatedTime, Transformation t) {
            int targetTop = 0;
            int endTarget = (int) (mTargetCirclePosition);
            if (mFrom != endTarget) {
                targetTop = (mFrom + (int) ((endTarget - mFrom) * interpolatedTime));
            }
            int offset = targetTop - mCircleView.getTop();
            setTargetOffsetTopAndBottom(offset, false /* requires update */);
        }
    };

    private final Animation mAnimateToStartPosition = new Animation() {
        @Override
        public void applyTransformation(float interpolatedTime, Transformation t) {
            int targetTop = 0;
            if (mFrom != mOriginalOffsetTop) {
                targetTop = (mFrom + (int) ((mOriginalOffsetTop - mFrom) * interpolatedTime));
            }
            int offset = targetTop - mCircleView.getTop();
            setTargetOffsetTopAndBottom(offset, false /* requires update */);
        }
    };

    private void setTargetOffsetTopAndBottom(int offset, boolean requiresUpdate) {
        mCircleView.bringToFront();
        mCircleView.offsetTopAndBottom(offset);
        mCurrentTargetOffsetTop = mCircleView.getTop();
        if (requiresUpdate && android.os.Build.VERSION.SDK_INT <= 10) {
            mCircleView.invalidate();
        }
    }

    private void onSecondaryPointerUp(MotionEvent ev) {
        final int pointerIndex = MotionEventCompat.getActionIndex(ev);
        final int pointerId = MotionEventCompat.getPointerId(ev, pointerIndex);
        if (pointerId == mActivePointerId) {
            // This was our active pointer going up. Choose a new
            // active pointer and adjust accordingly.
            final int newPointerIndex = pointerIndex == 0 ? 1 : 0;
            mActivePointerId = MotionEventCompat.getPointerId(ev, newPointerIndex);
        }
    }

    /**
     * Classes that wish to be notified when the swipe gesture correctly
     * triggers a refresh should implement this interface.
     */
    public interface OnRefreshListener {
        public void onRefresh();
    }
}