在上一篇android仿iPhone滚轮控件实现及源码分析（一）简单的说了下架构还有效果图，但是关于图形的绘制各方面的代码在532行到940行，如果写在一篇文章里面，可能会导致文章太长，效果不好，所以自作聪明的分成了两篇。闲言碎语不要讲，下面开始正事。
首先，先把代码贴出来：
/**
* Calculates control width and creates text layouts
* @param widthSize the input layout width
* @param mode the layout mode
* @return the calculated control width
*/
private int calculateLayoutWidth(int widthSize, int mode) {
initResourcesIfNecessary();
int width = widthSize;
int maxLength = getMaxTextLength();
if (maxLength > 0) {
float textWidth = FloatMath.ceil(Layout.getDesiredWidth("0", itemsPaint));
itemsWidth = (int) (maxLength * textWidth);
} else {
itemsWidth = 0;
}
itemsWidth += ADDITIONAL_ITEMS_SPACE; // make it some more
labelWidth = 0;
if (label != null && label.length() > 0) {
labelWidth = (int) FloatMath.ceil(Layout.getDesiredWidth(label, valuePaint));
}
boolean recalculate = false;
if (mode == MeasureSpec.EXACTLY) {
width = widthSize;
recalculate = true;
} else {
width = itemsWidth + labelWidth + 2 * PADDING;
if (labelWidth > 0) {
width += LABEL_OFFSET;
}
// Check against our minimum width
width = Math.max(width, getSuggestedMinimumWidth());
if (mode == MeasureSpec.AT_MOST && widthSize < width) {
width = widthSize;
recalculate = true;
}
}
if (recalculate) {
// recalculate width
int pureWidth = width - LABEL_OFFSET - 2 * PADDING;
if (pureWidth <= 0) {
itemsWidth = labelWidth = 0;
}
if (labelWidth > 0) {
double newWidthItems = (double) itemsWidth * pureWidth
/ (itemsWidth + labelWidth);
itemsWidth = (int) newWidthItems;
labelWidth = pureWidth - itemsWidth;
} else {
itemsWidth = pureWidth + LABEL_OFFSET; // no label
}
}
if (itemsWidth > 0) {
createLayouts(itemsWidth, labelWidth);
}
return width;
}
/**
* Creates layouts
* @param widthItems width of items layout
* @param widthLabel width of label layout
*/
private void createLayouts(int widthItems, int widthLabel) {
if (itemsLayout == null || itemsLayout.getWidth() > widthItems) {
itemsLayout = new StaticLayout(buildText(isScrollingPerformed), itemsPaint, widthItems,
widthLabel > 0 ? Layout.Alignment.ALIGN_OPPOSITE : Layout.Alignment.ALIGN_CENTER,
1, ADDITIONAL_ITEM_HEIGHT, false);
} else {
itemsLayout.increaseWidthTo(widthItems);
}
if (!isScrollingPerformed && (valueLayout == null || valueLayout.getWidth() > widthItems)) {
String text = getAdapter() != null ? getAdapter().getItem(currentItem) : null;
valueLayout = new StaticLayout(text != null ? text : "",
valuePaint, widthItems, widthLabel > 0 ?
Layout.Alignment.ALIGN_OPPOSITE : Layout.Alignment.ALIGN_CENTER,
1, ADDITIONAL_ITEM_HEIGHT, false);
} else if (isScrollingPerformed) {
valueLayout = null;
} else {
valueLayout.increaseWidthTo(widthItems);
}
if (widthLabel > 0) {
if (labelLayout == null || labelLayout.getWidth() > widthLabel) {
labelLayout = new StaticLayout(label, valuePaint,
widthLabel, Layout.Alignment.ALIGN_NORMAL, 1,
ADDITIONAL_ITEM_HEIGHT, false);
} else {
labelLayout.increaseWidthTo(widthLabel);
}
}
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
int width = calculateLayoutWidth(widthSize, widthMode);
int height;
if (heightMode == MeasureSpec.EXACTLY) {
height = heightSize;
} else {
height = getDesiredHeight(itemsLayout);
if (heightMode == MeasureSpec.AT_MOST) {
height = Math.min(height, heightSize);
}
}
setMeasuredDimension(width, height);
}
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (itemsLayout == null) {
if (itemsWidth == 0) {
calculateLayoutWidth(getWidth(), MeasureSpec.EXACTLY);
} else {
createLayouts(itemsWidth, labelWidth);
}
}
if (itemsWidth > 0) {
canvas.save();
// Skip padding space and hide a part of top and bottom items
canvas.translate(PADDING, -ITEM_OFFSET);
drawItems(canvas);
drawValue(canvas);
canvas.restore();
}
drawCenterRect(canvas);
drawShadows(canvas);
}
/**
* Draws shadows on top and bottom of control
* @param canvas the canvas for drawing
*/
private void drawShadows(Canvas canvas) {
topShadow.setBounds(0, 0, getWidth(), getHeight() / visibleItems);
topShadow.draw(canvas);
bottomShadow.setBounds(0, getHeight() - getHeight() / visibleItems,
getWidth(), getHeight());
bottomShadow.draw(canvas);
}
/**
* Draws value and label layout
* @param canvas the canvas for drawing
*/
private void drawValue(Canvas canvas) {
valuePaint.setColor(VALUE_TEXT_COLOR);
valuePaint.drawableState = getDrawableState();
Rect bounds = new Rect();
itemsLayout.getLineBounds(visibleItems / 2, bounds);
// draw label
if (labelLayout != null) {
canvas.save();
canvas.translate(itemsLayout.getWidth() + LABEL_OFFSET, bounds.top);
labelLayout.draw(canvas);
canvas.restore();
}
// draw current value
if (valueLayout != null) {
canvas.save();
canvas.translate(0, bounds.top + scrollingOffset);
valueLayout.draw(canvas);
canvas.restore();
}
}
/**
* Draws items
* @param canvas the canvas for drawing
*/
private void drawItems(Canvas canvas) {
canvas.save();
int top = itemsLayout.getLineTop(1);
canvas.translate(0, - top + scrollingOffset);
itemsPaint.setColor(ITEMS_TEXT_COLOR);
itemsPaint.drawableState = getDrawableState();
itemsLayout.draw(canvas);
canvas.restore();
}
/**
* Draws rect for current value
* @param canvas the canvas for drawing
*/
private void drawCenterRect(Canvas canvas) {
int center = getHeight() / 2;
int offset = getItemHeight() / 2;
centerDrawable.setBounds(0, center - offset, getWidth(), center + offset);
centerDrawable.draw(canvas);
}
@Override
public boolean onTouchEvent(MotionEvent event) {
WheelAdapter adapter = getAdapter();
if (adapter == null) {
return true;
}
if (!gestureDetector.onTouchEvent(event) && event.getAction() == MotionEvent.ACTION_UP) {
justify();
}
return true;
}
/**
* Scrolls the wheel
* @param delta the scrolling value
*/
private void doScroll(int delta) {
scrollingOffset += delta;
int count = scrollingOffset / getItemHeight();
int pos = currentItem - count;
if (isCyclic && adapter.getItemsCount() > 0) {
// fix position by rotating
while (pos < 0) {
pos += adapter.getItemsCount();
}
pos %= adapter.getItemsCount();
} else if (isScrollingPerformed) {
//
if (pos < 0) {
count = currentItem;
pos = 0;
} else if (pos >= adapter.getItemsCount()) {
count = currentItem - adapter.getItemsCount() + 1;
pos = adapter.getItemsCount() - 1;
}
} else {
// fix position
pos = Math.max(pos, 0);
pos = Math.min(pos, adapter.getItemsCount() - 1);
}
int offset = scrollingOffset;
if (pos != currentItem) {
setCurrentItem(pos, false);
} else {
invalidate();
}
// update offset
scrollingOffset = offset - count * getItemHeight();
if (scrollingOffset > getHeight()) {
scrollingOffset = scrollingOffset % getHeight() + getHeight();
}
}
// gesture listener
private SimpleOnGestureListener gestureListener = new SimpleOnGestureListener() {
public boolean onDown(MotionEvent e) {
if (isScrollingPerformed) {
scroller.forceFinished(true);
clearMessages();
return true;
}
return false;
}
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
startScrolling();
doScroll((int)-distanceY);
return true;
}
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
lastScrollY = currentItem * getItemHeight() + scrollingOffset;
int maxY = isCyclic ? 0x7FFFFFFF : adapter.getItemsCount() * getItemHeight();
int minY = isCyclic ? -maxY : 0;
scroller.fling(0, lastScrollY, 0, (int) -velocityY / 2, 0, 0, minY, maxY);
setNextMessage(MESSAGE_SCROLL);
return true;
}
};
// Messages
private final int MESSAGE_SCROLL = 0;
private final int MESSAGE_JUSTIFY = 1;
/**
* Set next message to queue. Clears queue before.
*
* @param message the message to set
*/
private void setNextMessage(int message) {
clearMessages();
animationHandler.sendEmptyMessage(message);
}
/**
* Clears messages from queue
*/
private void clearMessages() {
animationHandler.removeMessages(MESSAGE_SCROLL);
animationHandler.removeMessages(MESSAGE_JUSTIFY);
}
// animation handler
private Handler animationHandler = new Handler() {
public void handleMessage(Message msg) {
scroller.computeScrollOffset();
int currY = scroller.getCurrY();
int delta = lastScrollY - currY;
lastScrollY = currY;
if (delta != 0) {
doScroll(delta);
}
// scrolling is not finished when it comes to final Y
// so, finish it manually
if (Math.abs(currY - scroller.getFinalY()) < MIN_DELTA_FOR_SCROLLING) {
currY = scroller.getFinalY();
scroller.forceFinished(true);
}
if (!scroller.isFinished()) {
animationHandler.sendEmptyMessage(msg.what);
} else if (msg.what == MESSAGE_SCROLL) {
justify();
} else {
finishScrolling();
}
}
};
/**
* Justifies wheel
*/
private void justify() {
if (adapter == null) {
return;
}
lastScrollY = 0;
int offset = scrollingOffset;
int itemHeight = getItemHeight();
boolean needToIncrease = offset > 0 ? currentItem < adapter.getItemsCount() : currentItem > 0;
if ((isCyclic || needToIncrease) && Math.abs((float) offset) > (float) itemHeight / 2) {
if (offset < 0)
offset += itemHeight + MIN_DELTA_FOR_SCROLLING;
else
offset -= itemHeight + MIN_DELTA_FOR_SCROLLING;
}
if (Math.abs(offset) > MIN_DELTA_FOR_SCROLLING) {
scroller.startScroll(0, 0, 0, offset, SCROLLING_DURATION);
setNextMessage(MESSAGE_JUSTIFY);
} else {
finishScrolling();
}
}
/**
* Starts scrolling
*/
private void startScrolling() {
if (!isScrollingPerformed) {
isScrollingPerformed = true;
notifyScrollingListenersAboutStart();
}
}
/**
* Finishes scrolling
*/
void finishScrolling() {
if (isScrollingPerformed) {
notifyScrollingListenersAboutEnd();
isScrollingPerformed = false;
}
invalidateLayouts();
invalidate();
}
/**
* Scroll the wheel
* @param itemsToSkip items to scroll
* @param time scrolling duration
*/
public void scroll(int itemsToScroll, int time) {
scroller.forceFinished(true);
lastScrollY = scrollingOffset;
int offset = itemsToScroll * getItemHeight();
scroller.startScroll(0, lastScrollY, 0, offset - lastScrollY, time);
setNextMessage(MESSAGE_SCROLL);
startScrolling();
}
在629行到744行的代码是绘制图形，747行onTouchEvent()里面主要是调用了882行的justify()方法，用于调整画面，
@Override
public boolean onTouchEvent(MotionEvent event) {
WheelAdapter adapter = getAdapter();
if (adapter == null) {
return true;
}
if (!gestureDetector.onTouchEvent(event) && event.getAction() == MotionEvent.ACTION_UP) {
justify();
}
return true;
}
/**
* Justifies wheel
*/
private void justify() {
if (adapter == null) {
return;
}
lastScrollY = 0;
int offset = scrollingOffset;
int itemHeight = getItemHeight();
boolean needToIncrease = offset > 0 ? currentItem < adapter.getItemsCount() : currentItem > 0;
if ((isCyclic || needToIncrease) && Math.abs((float) offset) > (float) itemHeight / 2) {
if (offset < 0)
offset += itemHeight + MIN_DELTA_FOR_SCROLLING;
else
offset -= itemHeight + MIN_DELTA_FOR_SCROLLING;
}
if (Math.abs(offset) > MIN_DELTA_FOR_SCROLLING) {
scroller.startScroll(0, 0, 0, offset, SCROLLING_DURATION);
setNextMessage(MESSAGE_JUSTIFY);
} else {
finishScrolling();
}
}
我们看下重写的系统回调函数onMeasure()(用于测量各个控件距离，父子控件空间大小等)：
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
int widthMode = MeasureSpec.getMode(widthMeasureSpec);
int heightMode = MeasureSpec.getMode(heightMeasureSpec);
int widthSize = MeasureSpec.getSize(widthMeasureSpec);
int heightSize = MeasureSpec.getSize(heightMeasureSpec);
int width = calculateLayoutWidth(widthSize, widthMode);
int height;
if (heightMode == MeasureSpec.EXACTLY) {
height = heightSize;
} else {
height = getDesiredHeight(itemsLayout);
if (heightMode == MeasureSpec.AT_MOST) {
height = Math.min(height, heightSize);
}
}
setMeasuredDimension(width, height);
}
里面用到了532行calculateLayoutWidth()的方法，就是计算Layout的宽度，在calculateLayoutWidth()这个方法里面调用了
/**
* Creates layouts
* @param widthItems width of items layout
* @param widthLabel width of label layout
*/
private void createLayouts(int widthItems, int widthLabel) {
if (itemsLayout == null || itemsLayout.getWidth() > widthItems) {
itemsLayout = new StaticLayout(buildText(isScrollingPerformed), itemsPaint, widthItems,
widthLabel > 0 ? Layout.Alignment.ALIGN_OPPOSITE : Layout.Alignment.ALIGN_CENTER,
1, ADDITIONAL_ITEM_HEIGHT, false);
} else {
itemsLayout.increaseWidthTo(widthItems);
}
if (!isScrollingPerformed && (valueLayout == null || valueLayout.getWidth() > widthItems)) {
String text = getAdapter() != null ? getAdapter().getItem(currentItem) : null;
valueLayout = new StaticLayout(text != null ? text : "",
valuePaint, widthItems, widthLabel > 0 ?
Layout.Alignment.ALIGN_OPPOSITE : Layout.Alignment.ALIGN_CENTER,
1, ADDITIONAL_ITEM_HEIGHT, false);
} else if (isScrollingPerformed) {
valueLayout = null;
} else {
valueLayout.increaseWidthTo(widthItems);
}
if (widthLabel > 0) {
if (labelLayout == null || labelLayout.getWidth() > widthLabel) {
labelLayout = new StaticLayout(label, valuePaint,
widthLabel, Layout.Alignment.ALIGN_NORMAL, 1,
ADDITIONAL_ITEM_HEIGHT, false);
} else {
labelLayout.increaseWidthTo(widthLabel);
}
}
}
然后我们接着看onDraw()方法：
@Override
protected void onDraw(Canvas canvas) {
super.onDraw(canvas);
if (itemsLayout == null) {
if (itemsWidth == 0) {
calculateLayoutWidth(getWidth(), MeasureSpec.EXACTLY);
} else {
createLayouts(itemsWidth, labelWidth);
}
}
if (itemsWidth > 0) {
canvas.save();
// Skip padding space and hide a part of top and bottom items
canvas.translate(PADDING, -ITEM_OFFSET);
drawItems(canvas);
drawValue(canvas);
canvas.restore();
}
drawCenterRect(canvas);
drawShadows(canvas);
}
在onDraw方法中，也调用了CreateLayout()方法，然后在后面调用drawCenterRect()、drawItems()、drawValue()、绘制阴影drawShadows()两个方法：
/**
* Draws shadows on top and bottom of control
* @param canvas the canvas for drawing
*/
private void drawShadows(Canvas canvas) {
topShadow.setBounds(0, 0, getWidth(), getHeight() / visibleItems);
topShadow.draw(canvas);
bottomShadow.setBounds(0, getHeight() - getHeight() / visibleItems,
getWidth(), getHeight());
bottomShadow.draw(canvas);
}
/**
* Draws value and label layout
* @param canvas the canvas for drawing
*/
private void drawValue(Canvas canvas) {
valuePaint.setColor(VALUE_TEXT_COLOR);
valuePaint.drawableState = getDrawableState();
Rect bounds = new Rect();
itemsLayout.getLineBounds(visibleItems / 2, bounds);
// draw label
if (labelLayout != null) {
canvas.save();
canvas.translate(itemsLayout.getWidth() + LABEL_OFFSET, bounds.top);
labelLayout.draw(canvas);
canvas.restore();
}
// draw current value
if (valueLayout != null) {
canvas.save();
canvas.translate(0, bounds.top + scrollingOffset);
valueLayout.draw(canvas);
canvas.restore();
}
}
/**
* Draws items
* @param canvas the canvas for drawing
*/
private void drawItems(Canvas canvas) {
canvas.save();
int top = itemsLayout.getLineTop(1);
canvas.translate(0, - top + scrollingOffset);
itemsPaint.setColor(ITEMS_TEXT_COLOR);
itemsPaint.drawableState = getDrawableState();
itemsLayout.draw(canvas);
canvas.restore();
}
/**
* Draws rect for current value
* @param canvas the canvas for drawing
*/
private void drawCenterRect(Canvas canvas) {
int center = getHeight() / 2;
int offset = getItemHeight() / 2;
centerDrawable.setBounds(0, center - offset, getWidth(), center + offset);
centerDrawable.draw(canvas);
}
主要就是通过canvas类进行图形的绘制。
最后，我们看下840行定义的手势监听：
// gesture listener
private SimpleOnGestureListener gestureListener = new SimpleOnGestureListener() {
public boolean onDown(MotionEvent e) {
if (isScrollingPerformed) {
scroller.forceFinished(true);
clearMessages();
return true;
}
return false;
}
public boolean onScroll(MotionEvent e1, MotionEvent e2, float distanceX, float distanceY) {
startScrolling();
doScroll((int)-distanceY);
return true;
}
public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX, float velocityY) {
lastScrollY = currentItem * getItemHeight() + scrollingOffset;
int maxY = isCyclic ? 0x7FFFFFFF : adapter.getItemsCount() * getItemHeight();
int minY = isCyclic ? -maxY : 0;
scroller.fling(0, lastScrollY, 0, (int) -velocityY / 2, 0, 0, minY, maxY);
setNextMessage(MESSAGE_SCROLL);
return true;
}
};
里面主要调用的方法：clearMessages()、startScrolling()、doScroll()、setNextMessage()，先看下中间的两个方法开始滑动和滑动
/**
* Scrolls the wheel
* @param delta the scrolling value
*/
private void doScroll(int delta) {
scrollingOffset += delta;
int count = scrollingOffset / getItemHeight();
int pos = currentItem - count;
if (isCyclic && adapter.getItemsCount() > 0) {
// fix position by rotating
while (pos < 0) {
pos += adapter.getItemsCount();
}
pos %= adapter.getItemsCount();
} else if (isScrollingPerformed) {
//
if (pos < 0) {
count = currentItem;
pos = 0;
} else if (pos >= adapter.getItemsCount()) {
count = currentItem - adapter.getItemsCount() + 1;
pos = adapter.getItemsCount() - 1;
}
} else {
// fix position
pos = Math.max(pos, 0);
pos = Math.min(pos, adapter.getItemsCount() - 1);
}
int offset = scrollingOffset;
if (pos != currentItem) {
setCurrentItem(pos, false);
} else {
invalidate();
}
// update offset
scrollingOffset = offset - count * getItemHeight();
if (scrollingOffset > getHeight()) {
scrollingOffset = scrollingOffset % getHeight() + getHeight();
}
}
/**
* Starts scrolling
*/
private void startScrolling() {
if (!isScrollingPerformed) {
isScrollingPerformed = true;
notifyScrollingListenersAboutStart();
}
}
在startScrolling方法里面有287行的notifyScrollingListenersAboutStart函数。
再看clearMessages()、setMessageNext()
private void setNextMessage(int message) {
clearMessages();
animationHandler.sendEmptyMessage(message);
}
/**
* Clears messages from queue
*/
private void clearMessages() {
animationHandler.removeMessages(MESSAGE_SCROLL);
animationHandler.removeMessages(MESSAGE_JUSTIFY);
}
里面使用到了animationHandler，用来传递动画有段的操作：
// animation handler
private Handler animationHandler = new Handler() {
public void handleMessage(Message msg) {
scroller.computeScrollOffset();
int currY = scroller.getCurrY();
int delta = lastScrollY - currY;
lastScrollY = currY;
if (delta != 0) {
doScroll(delta);
}
// scrolling is not finished when it comes to final Y
// so, finish it manually
if (Math.abs(currY - scroller.getFinalY()) < MIN_DELTA_FOR_SCROLLING) {
currY = scroller.getFinalY();
scroller.forceFinished(true);
}
if (!scroller.isFinished()) {
animationHandler.sendEmptyMessage(msg.what);
} else if (msg.what == MESSAGE_SCROLL) {
justify();
} else {
finishScrolling();
}
}
};
里面调用了finishScrolling()
/**
* Finishes scrolling
*/
void finishScrolling() {
if (isScrollingPerformed) {
notifyScrollingListenersAboutEnd();
isScrollingPerformed = false;
}
invalidateLayouts();
invalidate();
}
