向納什致敬，鳳凰城永遠的英雄！phoenix

Yalantis 致力於提供世界一流的 Android 和 iOS 應用開發服務，因一些

動畫很棒的開源庫為大家所熟知

Phoenix-Android 旨在提供一個簡單的可定製的下拉重新整理功能。

<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>  
 

首先看他的構造方法

public PullToRefreshView(Context context, AttributeSet attrs) {
	super(context, attrs);
	TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.RefreshView);
	final int type = a.getInteger(R.styleable.RefreshView_type, STYLE_SUN);
	a.recycle();

	mDecelerateInterpolator = new DecelerateInterpolator(DECELERATE_INTERPOLATION_FACTOR);
	mTouchSlop = ViewConfiguration.get(context).getScaledTouchSlop();
	mTotalDragDistance = Utils.convertDpToPixel(context, DRAG_MAX_DISTANCE);

	mRefreshView = new ImageView(context);

	setRefreshStyle(type);

	addView(mRefreshView);
	//保證ondraw會執行，如果是true的話ondraw不會執行
	setWillNotDraw(false);
	ViewCompat.setChildrenDrawingOrderEnabled(this, true);
}
 

public void setRefreshStyle(int type) {
	setRefreshing(false);
	switch (type) {
		case STYLE_SUN:
			mBaseRefreshView = new SunRefreshView(getContext(), this);
			break;
		default:
			throw new InvalidParameterException("Type does not exist");
	}
	mRefreshView.setImageDrawable(mBaseRefreshView);
}

onMeasure

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
	super.onMeasure(widthMeasureSpec, heightMeasureSpec);

	ensureTarget();
	if (mTarget == null)
		return;

	widthMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredWidth() - getPaddingRight() - getPaddingLeft(), MeasureSpec.EXACTLY);
	heightMeasureSpec = MeasureSpec.makeMeasureSpec(getMeasuredHeight() - getPaddingTop() - getPaddingBottom(), MeasureSpec.EXACTLY);
	mTarget.measure(widthMeasureSpec, heightMeasureSpec);
	mRefreshView.measure(widthMeasureSpec, heightMeasureSpec);
}

private void ensureTarget() {
	if (mTarget != null)
		return;
	if (getChildCount() > 0) {
		for (int i = 0; i < getChildCount(); i++) {
			View child = getChildAt(i);
			if (child != mRefreshView) {
				mTarget = child;
				mTargetPaddingBottom = mTarget.getPaddingBottom();
				mTargetPaddingLeft = mTarget.getPaddingLeft();
				mTargetPaddingRight = mTarget.getPaddingRight();
				mTargetPaddingTop = mTarget.getPaddingTop();
			}
		}
	}
}

一開始mTarget 是空的，然後到getChildCount方法，想一下這個時候這個viewgroup中也就兩個孩子，一個imageview，一個listview，ensureTarget的作用就是把listview的例項賦值給mTarget，以及給幾個padding賦值，隨後在onmeasure中設定imageview和listview與外層的viewgroup一樣大小。

@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {

	ensureTarget();
	if (mTarget == null)
		return;

	int height = getMeasuredHeight();
	int width = getMeasuredWidth();
	int left = getPaddingLeft();
	int top = getPaddingTop();
	int right = getPaddingRight();
	int bottom = getPaddingBottom();

	mTarget.layout(left, top + mCurrentOffsetTop, left + width - right, top + height - bottom + mCurrentOffsetTop);
	mRefreshView.layout(left, top, left + width - right, top + height - bottom);
}

ontouchevent和onInterceptTouchEvent

@Override
public boolean onInterceptTouchEvent(MotionEvent ev) {

	if (!isEnabled() || canChildScrollUp() || mRefreshing) {
		return false;
	}

	final int action = MotionEventCompat.getActionMasked(ev);

	switch (action) {
		case MotionEvent.ACTION_DOWN:
			setTargetOffsetTop(0, true);
			mActivePointerId = MotionEventCompat.getPointerId(ev, 0);
			mIsBeingDragged = false;
			final float initialMotionY = getMotionEventY(ev, mActivePointerId);
			if (initialMotionY == -1) {
				return false;
			}
			mInitialMotionY = initialMotionY;
			break;
		case MotionEvent.ACTION_MOVE:
			if (mActivePointerId == INVALID_POINTER) {
				return false;
			}
			final float y = getMotionEventY(ev, mActivePointerId);
			if (y == -1) {
				return false;
			}
			final float yDiff = y - mInitialMotionY;
			if (yDiff > mTouchSlop && !mIsBeingDragged) {
				mIsBeingDragged = true;
			}
			break;
		case MotionEvent.ACTION_UP:
		case MotionEvent.ACTION_CANCEL:
			mIsBeingDragged = false;
			mActivePointerId = INVALID_POINTER;
			break;
		case MotionEventCompat.ACTION_POINTER_UP:
			onSecondaryPointerUp(ev);
			break;
	}

	return mIsBeingDragged;
}

@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);


            mBaseRefreshView.setPercent(mCurrentDragPercent, true);
            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;
                animateOffsetToStartPosition();
            }
            mActivePointerId = INVALID_POINTER;
            return false;
        }
    }


    return true;
}

頭部動畫效果

@Override
public void draw(Canvas canvas) {
	if (mScreenWidth <= 0) return;

	final int saveCount = canvas.save();

	canvas.translate(0, mTop);
	canvas.clipRect(0, -mTop, mScreenWidth, mParent.getTotalDragDistance());

	drawSky(canvas);
	drawSun(canvas);
	drawTown(canvas);

	canvas.restoreToCount(saveCount);
}

示例程式碼：

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);
    }
 });