Android 横向ListView实现，Kafka是如何实现高性能的

Android 横向ListView实现，Kafka是如何实现高性能的

private boolean mDataChanged = false;

public HorizontalListView(Context context, AttributeSet attrs) {

super(context, attrs);

initView();

}

private synchronized void initView() {

mLeftViewIndex = -1;

mRightViewIndex = 0;

mDisplayOffset = 0;

mCurrentX = 0;

mNextX = 0;

mMaxX = Integer.MAX_VALUE;

mScroller = new Scroller(getContext());

mGesture = new GestureDetector(getContext(), mOnGesture);

}

@Override

public void setonItemSelectedListener(onItemSelectedListener listener) {

monItemSelected = listener;

}

@Override

public void setonItemClickListener(onItemClickListener listener){

monItemClicked = listener;

}

@Override

public void setonItemLongClickListener(onItemLongClickListener listener) {

monItemLongClicked = listener;

}

private DataSetObserver mDataObserver = new DataSetObserver() {

@Override

public void onChanged() {

synchronized(HorizontalListView.this){

mDataChanged = true;

}

invalidate();

requestLayout();

}

@Override

public void onInvalidated() {

reset();

invalidate();

requestLayout();

}

};

public boolean onInterceptTouchEvent(MotionEvent ev) {

getParent().requestDisallowInterceptTouchEvent(true);

return mGesture.onTouchEvent(ev);

};

@Override

public ListAdapter getAdapter() {

return mAdapter;

}

@Override

public View getSelectedView() {

return null;

}

@Override

public void setAdapter(ListAdapter adapter) {

if(mAdapter != null) {

mAdapter.unregisterDataSetObserver(mDataObserver);

}

mAdapter = adapter;

mAdapter.registerDataSetObserver(mDataObserver);

reset();

}

private synchronized void reset(){

initView();

removeAllViewsInLayout();

requestLayout();

}

@Override

public void setSelection(int position) {

}

private void addAndMeasureChild(final View child, int viewPos) {

LayoutParams params = child.getLayoutParams();

if(params == null) {

params = new LayoutParams(LayoutParams.FILL_PARENT, LayoutParams.FILL_PARENT);

}

addViewInLayout(child, viewPos, params, true);

child.measure(MeasureSpec.makeMeasureSpec(getWidth(), MeasureSpec.AT_MOST),

MeasureSpec.makeMeasureSpec(getHeight(), MeasureSpec.AT_MOST));

}

@Override

protected synchronized void onLayout(boolean changed, int left, int top, int right, int bottom) {

super.onLayout(changed, left, top, right, bottom);

if(mAdapter == null){

return;

}

if(mDataChanged){

int oldCurrentX = mCurrentX;

initView();

removeAllViewsInLayout();

mNextX = oldCurrentX;

mDataChanged = false;

}

if(mScroller.computeScrollOffset()){

int scrollx = mScroller.getCurrX();

mNextX = scrollx;

}

if(mNextX <= 0){

mNextX = 0;

mScroller.forceFinished(true);

}

if(mNextX >= mMaxX) {

mNextX = mMaxX;

mScroller.forceFinished(true);

}

int dx = mCurrentX - mNextX;

removeNonVisibleItems(dx);

fillList(dx);

positionItems(dx);

mCurrentX = mNextX;

if(!mScroller.isFinished()){

post(new Runnable(){

@Override

public void run() {

requestLayout();

}

});

}

}

private void fillList(final int dx) {

int edge = 0;

View child = getChildAt(getChildCount()-1);

if(child != null) {

edge = child.getRight();

}

fillListRight(edge, dx);

edge = 0;

child = getChildAt(0);

if(child != null) {

edge = child.getLeft();

}

fillListLeft(edge, dx);

}

private void fillListRight(int rightEdge, final int dx) {

while(rightEdge + dx < getWidth() && mRightViewIndex < mAdapter.getCount()) {

View child = mAdapter.getView(mRightViewIndex, mRemovedViewQueue.poll(), this);

addAndMeasureChild(child, -1);

rightEdge += child.getMeasuredWidth();

if(mRightViewIndex == mAdapter.getCount()-1) {

mMaxX = mCurrentX + rightEdge - getWidth();

}

if (mMaxX < 0) {

mMaxX = 0;

}

mRightViewIndex++;

}

}

private void fillListLeft(int leftEdge, final int dx) {

while(leftEdge + dx > 0 && mLeftViewIndex >= 0) {

View child = mAdapter.getView(mLeftViewIndex, mRemovedViewQueue.poll(), this);

addAndMeasureChild(child, 0);

leftEdge -= child.getMeasuredWidth();

mLeftViewIndex–;

mDisplayOffset -= child.getMeasuredWidth();

}

}

private void removeNonVisibleItems(final int dx) {

View child = getChildAt(0);

while(child != null && child.getRight() + dx <= 0) {

mDisplayOffset += child.getMeasuredWidth();

mRemovedViewQueue.offer(child);

removeViewInLayout(child);

mLeftViewIndex++;

child = getChildAt(0);

}

child = getChildAt(getChildCount()-1);

while(child != null && child.getLeft() + dx >= getWidth()) {

mRemovedViewQueue.offer(child);

removeViewInLayout(child);

mRightViewIndex–;

child = getChildAt(getChildCount()-1);

}

}

private void positionItems(final int dx) {

if(getChildCount() > 0){

mDisplayOffset += dx;

int left = mDisplayOffset;

for(int i=0;i

View child = getChildAt(i);

int childWidth = child.getMeasuredWidth();

child.layout(left, 0, left + childWidth, child.getMeasuredHeight());

left += childWidth + child.getPaddingRight();

}

}

}

public synchronized void scrollTo(int x) {

mScroller.startScroll(mNextX, 0, x -

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mNextX, 0);

requestLayout();

}

@Override

public boolean dispatchTouchEvent(MotionEvent ev) {

boolean handled = super.dispatchTouchEvent(ev);

handled |= mGesture.onTouchEvent(ev);

return handled;

}

protected boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,

float velocityY) {

synchronized(HorizontalListView.this){

mScroller.fling(mNextX, 0, (int)-velocityX, 0, 0, mMaxX, 0, 0);

}

requestLayout();

return true;

}

protected boolean onDown(MotionEvent e) {

mScroller.forceFinished(true);

return true;

}

private onGestureListener monGesture = new GestureDetector.SimpleonGestureListener() {

@Override

public boolean onDown(MotionEvent e) {

return HorizontalListView.this.onDown(e);

}

@Override

public boolean onFling(MotionEvent e1, MotionEvent e2, float velocityX,

float velocityY) {

return HorizontalListView.this.onFling(e1, e2, velocityX, velocityY);

}

总结

最后为了帮助大家深刻理解Android相关知识点的原理以及面试相关知识，这里放上相关的我搜集整理的14套腾讯、字节跳动、阿里、百度等2021面试真题解析，我把技术点整理成了视频和PDF（实际上比预期多花了不少精力），包知识脉络 + 诸多细节。

网上学习 Android的资料一大堆，但如果学到的知识不成体系，遇到问题时只是浅尝辄止，不再深入研究，那么很难做到真正的技术提升。希望这份系统化的技术体系对大家有一个方向参考。

locityX,

float velocityY) {

return HorizontalListView.this.onFling(e1, e2, velocityX, velocityY);

}

总结

最后为了帮助大家深刻理解Android相关知识点的原理以及面试相关知识，这里放上相关的我搜集整理的14套腾讯、字节跳动、阿里、百度等2021面试真题解析，我把技术点整理成了视频和PDF（实际上比预期多花了不少精力），包知识脉络 + 诸多细节。

[外链图片转存中…(img-ObHQ2mVT-1640921790477)]
[外链图片转存中…(img-KF4KoPR2-1640921790479)]

[外链图片转存中…(img-cqpHL0ev-1640921790479)]

[外链图片转存中…(img-UtEeToWI-1640921790480)]
网上学习 Android的资料一大堆，但如果学到的知识不成体系，遇到问题时只是浅尝辄止，不再深入研究，那么很难做到真正的技术提升。希望这份系统化的技术体系对大家有一个方向参考。

[外链图片转存中…(img-k94dQ2vf-1640921790480)]

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