Android源码解析－－超好看的下拉刷新动画

private void initiateDimens() {
        mScreenWidth = mContext.getResources().getDisplayMetrics().widthPixels;
        mJetTopOffset = mParent.getTotalDragDistance() * 0.5f;
        mTop = -mParent.getTotalDragDistance();
    }

2.为头填充图片，设置图片的大小

private void createBitmaps() {
        mLeftClouds = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.clouds_left);
        mRightClouds = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.clouds_right);
        mFrontClouds = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.clouds_center);
        mJet = BitmapFactory.decodeResource(mContext.getResources(), R.drawable.airplane);

        mJetWidthCenter = mJet.getWidth() / 2;
        mJetHeightCenter = mJet.getHeight() / 2;
        mFrontCloudWidthCenter = mFrontClouds.getWidth() / 2;
        mFrontCloudHeightCenter = mFrontClouds.getHeight() / 2;

        mRightCloudsWidthCenter = mRightClouds.getWidth() / 2;
        mRightCloudsHeightCenter = mRightClouds.getHeight() / 2;
        mLeftCloudsWidthCenter = mLeftClouds.getWidth() / 2;
        mLeftCloudsHeightCenter = mLeftClouds.getHeight() / 2;
    }

3.然后我们来画这个头

public void draw(@NonNull Canvas canvas) {
        final int saveCount = canvas.save();

        // DRAW BACKGROUND.
        canvas.drawColor(mContext.getResources().getColor(R.color.sky_background));

        if (isRefreshing) {
            // Set up new set of wind
            while (mWinds.size() < WIND_SET_AMOUNT) {
                float y = (float) (mParent.getTotalDragDistance() / (Math.random() * RANDOM_Y_COEFFICIENT));
                float x = random(MIN_WIND_X_OFFSET, MAX_WIND_X_OFFSET);

                // Magic with checking interval between winds
                if (mWinds.size() > 1) {
                    y = 0;
                    while (y == 0) {
                        float tmp = (float) (mParent.getTotalDragDistance() / (Math.random() * RANDOM_Y_COEFFICIENT));

                        for (Map.Entry<Float, Float> wind : mWinds.entrySet()) {
                            // We want that interval will be greater than fifth part of draggable distance
                            if (Math.abs(wind.getKey() - tmp) > mParent.getTotalDragDistance() / RANDOM_Y_COEFFICIENT) {
                                y = tmp;
                            } else {
                                y = 0;
                                break;
                            }
                        }
                    }
                }

                mWinds.put(y, x);
                drawWind(canvas, y, x);
            }

            // Draw current set of wind
            if (mWinds.size() >= WIND_SET_AMOUNT) {
                for (Map.Entry<Float, Float> wind : mWinds.entrySet()) {
                    drawWind(canvas, wind.getKey(), wind.getValue());
                }
            }

            // We should to create new set of winds
            if (mInverseDirection && mNewWindSet) {
                mWinds.clear();
                mNewWindSet = false;
                mWindLineWidth = random(MIN_WIND_LINE_WIDTH, MAX_WIND_LINE_WIDTH);
            }

            // needed for checking direction
            mLastAnimationTime = mLoadingAnimationTime;
        }

        drawJet(canvas);
        drawSideClouds(canvas);
        drawCenterClouds(canvas);

        canvas.restoreToCount(saveCount);
    }

/**
     * Draw wind on loading animation
     *
     * @param canvas  - area where we will draw
     * @param y       - y position fot one of lines
     * @param xOffset - x offset for on of lines
     */
    private void drawWind(Canvas canvas, float y, float xOffset) {
        /* We should multiply current animation time with this coefficient for taking all screen width in time
        Removing slowing of animation with dividing on {@LINK #SLOW_DOWN_ANIMATION_COEFFICIENT}
        And we should don't forget about distance that should "fly" line that depend on screen of device and x offset
        */
        float cof = (mScreenWidth + xOffset) / (LOADING_ANIMATION_COEFFICIENT / SLOW_DOWN_ANIMATION_COEFFICIENT);
        float time = mLoadingAnimationTime;

        // HORRIBLE HACK FOR REVERS ANIMATION THAT SHOULD WORK LIKE RESTART ANIMATION
        if (mLastAnimationTime - mLoadingAnimationTime > 0) {
            mInverseDirection = true;
            // take time from 0 to end of animation time
            time = (LOADING_ANIMATION_COEFFICIENT / SLOW_DOWN_ANIMATION_COEFFICIENT) - mLoadingAnimationTime;
        } else {
            mNewWindSet = true;
            mInverseDirection = false;
        }

        // Taking current x position of drawing wind
        // For fully disappearing of line we should subtract wind line width
        float x = (mScreenWidth - (time * cof)) + xOffset - mWindLineWidth;
        float xEnd = x + mWindLineWidth;

        canvas.drawLine(x, y, xEnd, y, mWindPaint);
    }

    private void drawSideClouds(Canvas canvas) {
        Matrix matrixLeftClouds = mMatrix;
        Matrix matrixRightClouds = mAdditionalMatrix;
        matrixLeftClouds.reset();
        matrixRightClouds.reset();

        // Drag percent will newer get more then 1 here
        float dragPercent = Math.min(1f, Math.abs(mPercent));

        boolean overdrag = false;

        // But we check here for overdrag
        if (mPercent > 1.0f) {
            overdrag = true;
        }

        float scale;
        float scalePercentDelta = dragPercent - SCALE_START_PERCENT;
        if (scalePercentDelta > 0) {
            float scalePercent = scalePercentDelta / (1.0f - SCALE_START_PERCENT);
            scale = SIDE_CLOUDS_INITIAL_SCALE + (SIDE_CLOUDS_FINAL_SCALE - SIDE_CLOUDS_INITIAL_SCALE) * scalePercent;
        } else {
            scale = SIDE_CLOUDS_INITIAL_SCALE;
        }

        // Current y position of clouds
        float dragYOffset = mParent.getTotalDragDistance() * (1.0f - dragPercent);

        // Position where clouds fully visible on screen and we should drag them with content of listView
        int cloudsVisiblePosition = mParent.getTotalDragDistance() / 2 - mLeftCloudsHeightCenter;

        boolean needMoveCloudsWithContent = false;
        if (dragYOffset < cloudsVisiblePosition) {
            needMoveCloudsWithContent = true;
        }

        float offsetRightX = mScreenWidth - mRightClouds.getWidth();
        float offsetRightY = (needMoveCloudsWithContent
                ? mParent.getTotalDragDistance() * dragPercent - mLeftClouds.getHeight()
                : dragYOffset)
                + (overdrag ? mTop : 0);

        float offsetLeftX = 0;
        float offsetLeftY = (needMoveCloudsWithContent
                ? mParent.getTotalDragDistance() * dragPercent - mLeftClouds.getHeight()
                : dragYOffset)
                + (overdrag ? mTop : 0);

        // Magic with animation on loading process
        if (isRefreshing) {
            if (checkCurrentAnimationPart(AnimationPart.FIRST)) {
                offsetLeftY += getAnimationPartValue(AnimationPart.FIRST) / Y_SIDE_CLOUDS_SLOW_DOWN_COF;
                offsetRightX -= getAnimationPartValue(AnimationPart.FIRST) / X_SIDE_CLOUDS_SLOW_DOWN_COF;
            } else if (checkCurrentAnimationPart(AnimationPart.SECOND)) {
                offsetLeftY += getAnimationPartValue(AnimationPart.SECOND) / Y_SIDE_CLOUDS_SLOW_DOWN_COF;
                offsetRightX -= getAnimationPartValue(AnimationPart.SECOND) / X_SIDE_CLOUDS_SLOW_DOWN_COF;
            } else if (checkCurrentAnimationPart(AnimationPart.THIRD)) {
                offsetLeftY -= getAnimationPartValue(AnimationPart.THIRD) / Y_SIDE_CLOUDS_SLOW_DOWN_COF;
                offsetRightX += getAnimationPartValue(AnimationPart.THIRD) / X_SIDE_CLOUDS_SLOW_DOWN_COF;
            } else if (checkCurrentAnimationPart(AnimationPart.FOURTH)) {
                offsetLeftY -= getAnimationPartValue(AnimationPart.FOURTH) / X_SIDE_CLOUDS_SLOW_DOWN_COF;
                offsetRightX += getAnimationPartValue(AnimationPart.FOURTH) / Y_SIDE_CLOUDS_SLOW_DOWN_COF;
            }
        }

        matrixRightClouds.postScale(scale, scale, mRightCloudsWidthCenter, mRightCloudsHeightCenter);
        matrixRightClouds.postTranslate(offsetRightX, offsetRightY);

        matrixLeftClouds.postScale(scale, scale, mLeftCloudsWidthCenter, mLeftCloudsHeightCenter);
        matrixLeftClouds.postTranslate(offsetLeftX, offsetLeftY);

        canvas.drawBitmap(mLeftClouds, matrixLeftClouds, null);
        canvas.drawBitmap(mRightClouds, matrixRightClouds, null);
    }

    private void drawCenterClouds(Canvas canvas) {
        Matrix matrix = mMatrix;
        matrix.reset();
        float dragPercent = Math.min(1f, Math.abs(mPercent));

        float scale;
        float overdragPercent = 0;
        boolean overdrag = false;

        if (mPercent > 1.0f) {
            overdrag = true;
            // Here we want know about how mach percent of over drag we done
            overdragPercent = Math.abs(1.0f - mPercent);
        }

        float scalePercentDelta = dragPercent - SCALE_START_PERCENT;
        if (scalePercentDelta > 0) {
            float scalePercent = scalePercentDelta / (1.0f - SCALE_START_PERCENT);
            scale = CENTER_CLOUDS_INITIAL_SCALE + (CENTER_CLOUDS_FINAL_SCALE - CENTER_CLOUDS_INITIAL_SCALE) * scalePercent;
        } else {
            scale = CENTER_CLOUDS_INITIAL_SCALE;
        }

        float parallaxPercent = 0;
        boolean parallax = false;
        // Current y position of clouds
        float dragYOffset = mParent.getTotalDragDistance() * dragPercent;
        // Position when should start parallax scrolling
        int startParallaxHeight = mParent.getTotalDragDistance() - mFrontCloudHeightCenter;

        if (dragYOffset > startParallaxHeight) {
            parallax = true;
            parallaxPercent = dragYOffset - startParallaxHeight;
        }

        float offsetX = (mScreenWidth / 2) - mFrontCloudWidthCenter;
        float offsetY = dragYOffset
                - (parallax ? mFrontCloudHeightCenter + parallaxPercent : mFrontCloudHeightCenter)
                + (overdrag ? mTop : 0);

        float sx = overdrag ? scale + overdragPercent / 4 : scale;
        float sy = overdrag ? scale + overdragPercent / 2 : scale;

        if (isRefreshing && !overdrag) {
            if (checkCurrentAnimationPart(AnimationPart.FIRST)) {
                sx = scale - (getAnimationPartValue(AnimationPart.FIRST) / LOADING_ANIMATION_COEFFICIENT) / 8;
            } else if (checkCurrentAnimationPart(AnimationPart.SECOND)) {
                sx = scale - (getAnimationPartValue(AnimationPart.SECOND) / LOADING_ANIMATION_COEFFICIENT) / 8;
            } else if (checkCurrentAnimationPart(AnimationPart.THIRD)) {
                sx = scale + (getAnimationPartValue(AnimationPart.THIRD) / LOADING_ANIMATION_COEFFICIENT) / 6;
            } else if (checkCurrentAnimationPart(AnimationPart.FOURTH)) {
                sx = scale + (getAnimationPartValue(AnimationPart.FOURTH) / LOADING_ANIMATION_COEFFICIENT) / 6;
            }
            sy = sx;
        }

        matrix.postScale(sx, sy, mFrontCloudWidthCenter, mFrontCloudHeightCenter);
        matrix.postTranslate(offsetX, offsetY);

        canvas.drawBitmap(mFrontClouds, matrix, null);
    }

    private void drawJet(Canvas canvas) {
        Matrix matrix = mMatrix;
        matrix.reset();

        float dragPercent = mPercent;
        float rotateAngle = 0;

        // Check overdrag
        if (dragPercent > 1.0f && !mEndOfRefreshing) {
            rotateAngle = (dragPercent % 1) * 10;
            dragPercent = 1.0f;
        }

        float offsetX = ((mScreenWidth * dragPercent) / 2) - mJetWidthCenter;

        float offsetY = mJetTopOffset
                + (mParent.getTotalDragDistance() / 2)
                * (1.0f - dragPercent)
                - mJetHeightCenter;

        if (isRefreshing) {
            if (checkCurrentAnimationPart(AnimationPart.FIRST)) {
                offsetY -= getAnimationPartValue(AnimationPart.FIRST);
            } else if (checkCurrentAnimationPart(AnimationPart.SECOND)) {
                offsetY -= getAnimationPartValue(AnimationPart.SECOND);
            } else if (checkCurrentAnimationPart(AnimationPart.THIRD)) {
                offsetY += getAnimationPartValue(AnimationPart.THIRD);
            } else if (checkCurrentAnimationPart(AnimationPart.FOURTH)) {
                offsetY += getAnimationPartValue(AnimationPart.FOURTH);
            }
        }

        matrix.setTranslate(offsetX, offsetY);

        if (dragPercent == 1.0f) {
            matrix.preRotate(rotateAngle, mJetWidthCenter, mJetHeightCenter);
        }

        canvas.drawBitmap(mJet, matrix, null);
    }

private RefreshView mRefreshView;

<pre name="code" class="java">private ImageView mRefreshImageView;

<pre name="code" class="java">mRefreshImageView = new ImageView(context);
        mRefreshView = new RefreshView(getContext(), this);
        mRefreshImageView.setImageDrawable(mRefreshView);

        addView(mRefreshImageView);

2.然后我们设置OntouchEvent()事件

@Override
    public boolean onTouchEvent(@NonNull MotionEvent ev) {

        if (!mIsBeingDragged) {
            return super.onTouchEvent(ev);
        }

        final int action = MotionEventCompat.getActionMasked(ev);

        switch (action) {
            case MotionEvent.ACTION_MOVE: {
                final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
                if (pointerIndex < 0) {
                    return false;
                }

                final float y = MotionEventCompat.getY(ev, pointerIndex);
                final float yDiff = y - mInitialMotionY;
                final float scrollTop = yDiff * DRAG_RATE;
                mCurrentDragPercent = scrollTop / mTotalDragDistance;
                if (mCurrentDragPercent < 0) {
                    return false;
                }
                float boundedDragPercent = Math.min(1f, Math.abs(mCurrentDragPercent));
                float extraOS = Math.abs(scrollTop) - mTotalDragDistance;
                float slingshotDist = mTotalDragDistance;
                float tensionSlingshotPercent = Math.max(0,
                        Math.min(extraOS, slingshotDist * 2) / slingshotDist);
                float tensionPercent = (float) ((tensionSlingshotPercent / 4) - Math.pow(
                        (tensionSlingshotPercent / 4), 2)) * 2f;
                float extraMove = (slingshotDist) * tensionPercent / 2;
                int targetY = (int) ((slingshotDist * boundedDragPercent) + extraMove);

                mRefreshView.setPercent(mCurrentDragPercent);
                setTargetOffsetTop(targetY - mCurrentOffsetTop, true);
                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: {
                if (mActivePointerId == INVALID_POINTER) {
                    return false;
                }
                final int pointerIndex = MotionEventCompat.findPointerIndex(ev, mActivePointerId);
                final float y = MotionEventCompat.getY(ev, pointerIndex);
                final float overScrollTop = (y - mInitialMotionY) * DRAG_RATE;
                mIsBeingDragged = false;
                if (overScrollTop > mTotalDragDistance) {
                    setRefreshing(true, true);
                } else {
                    mRefreshing = false;
                    animateOffsetToPosition(mAnimateToStartPosition);
                }
                mActivePointerId = INVALID_POINTER;
                return false;
            }
        }

        return true;
    }

三、最后我们看怎样在Activity中使用这个下拉刷新控件

1.先看一下布局文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".PullToRefreshActivity">

    <com.hankkin.AnimationPullToRefreshDemo.PullToRefreshView
        android:id="@+id/pull_to_refresh"
        android:layout_width="match_parent"
        android:layout_height="match_parent">

        <ListView
            android:id="@+id/list_view"
            android:divider="@null"
            android:dividerHeight="0dp"
            android:fadingEdge="none"
            android:layout_width="match_parent"
            android:layout_height="match_parent" />

    </com.hankkin.AnimationPullToRefreshDemo.PullToRefreshView>

</RelativeLayout>

Map<String, Integer> map;
        List<Map<String, Integer>> sampleList = new ArrayList<Map<String, Integer>>();


        int[] colors = {
                R.color.saffron,
                R.color.eggplant,
                R.color.sienna};

        int[] tripNames = {
                R.string.trip_to_india,
                R.string.trip_to_italy,
                R.string.trip_to_indonesia};

        for (int i = 0; i < tripNames.length; i++) {
            map = new HashMap<String, Integer>();
            map.put(SampleAdapter.KEY_NAME, tripNames[i]);
            map.put(SampleAdapter.KEY_COLOR, colors[i]);
            sampleList.add(map);
        }

        ListView listView = (ListView) findViewById(R.id.list_view);
        listView.setAdapter(new SampleAdapter(this, R.layout.list_item, sampleList));

mPullToRefreshView = (PullToRefreshView) findViewById(R.id.pull_to_refresh);
        mPullToRefreshView.setOnRefreshListener(new PullToRefreshView.OnRefreshListener() {
            @Override
            public void onRefresh() {
                mPullToRefreshView.postDelayed(new Runnable() {
                    @Override
                    public void run() {
                        mPullToRefreshView.setRefreshing(false);
                    }
                }, REFRESH_DELAY);
            }
        });