RecyclerView一般作为Android显示列表的控件，有诸多优异的性能。
回收池策略能加载上亿级数据并不发生卡顿
适配器模式能展示任意显示需求
1、RecyclerView架构中核心组件
回收池：能回收任意Item控件，并返回符合类型的Item控件；比如onBindViewHolder方法中的第一个参数是从回收池中返回的
适配器：Adapter接口，经常辅助RecyclerView实现类表展示；适配器模式，将用户界面展示与交互分离
RecyclerView：是触摸事件的交互，主要实现边界值判断；根据用户的触摸反馈，协调回收池对象与适配器对象之间的工作。
2、RecyclerView架构实现
架构：充分利用传送带原理，只有用户看到的数据才会加载到内存，而看不到的在等待被加载。传送带能够源源不断的传送亿级货物，RecyclerView也能够显示加载亿级Item.
传送带的工作机制可以比作生产者与消费者模式。
下面就来手写实现一下RecyclerView：
/**
* 回收池
*/
public class Recycler {
private Stack[] views ;
public Recycler(int typeNumber) {
views = new Stack[typeNumber];
for (int i=0;i();
}
}
public void put(View view, int type){
views[type].push(view);
}
public View get(int type) {
try {
return views[type].pop();
} catch (Exception e) {
return null;
}
}
}
public class RecyclerView extends ViewGroup {
private Adapter adapter;
//当前显示的View
private List viewList;
//当前滑动的y值
private int currentY;
//行数
private int rowCount;
//view的第一行 是占内容的几行
private int firstRow;
//y偏移量
private int scrollY;
//初始化 第一屏最慢
private boolean needRelayout;
private int width;
private int height;
private int[] heights;//item 高度
Recycler recycler;//回收池
//最小滑动距离
private int touchSlop;
public Adapter getAdapter() {
return adapter;
}
public void setAdapter(Adapter adapter) {
this.adapter = adapter;
if (adapter != null) {
recycler = new Recycler(adapter.getViewTypeCount());//线程池
scrollY = 0;
firstRow = 0;
needRelayout = true;
requestLayout();//1 onMeasure 2 onLayout
}
}
public RecyclerView(Context context, AttributeSet attrs) {
super(context, attrs);
init(context, attrs);
}
private void init(Context context, AttributeSet attrs) {
ViewConfiguration configuration = ViewConfiguration.get(context);
this.touchSlop = configuration.getScaledTouchSlop();//获取最小滑动距离
this.viewList = new ArrayList<>();
this.needRelayout = true;
}
//初始化
@Override
protected void onLayout(boolean changed, int l, int t, int r, int b) {
if (needRelayout || changed) {
needRelayout = false;
viewList.clear();
removeAllViews();
if (adapter != null) {
//摆放
width = r - l;
height = b - t;
int left, top = 0, right, bottom;
for (int i = 0; i < rowCount && top < height; i++) {
right = width;
bottom = top + heights[i];
//生成一个View
View view = makeAndStep(i, 0, top, width, bottom);
viewList.add(view);
top = bottom;//循环摆放
}
}
}
}
private View makeAndStep(int row, int left, int top, int right, int bottom) {
View view = obtainView(row, right - left, bottom - top);
view.layout(left, top, right, bottom);
return view;
}
private View obtainView(int row, int width, int height) {
//key type
int itemType = adapter.getItemViewType(row);
//取不到
View reclyView = recycler.get(itemType);
View view = null;
if (reclyView == null) {
view = adapter.onCreateViewHodler(row, reclyView, this);
if (view == null) {
throw new RuntimeException("onCreateViewHodler 必须填充布局");
}
} else {
view = adapter.onBinderViewHodler(row, reclyView, this);
}
view.setTag(R.id.tag_type_view, itemType);
view.measure(MeasureSpec.makeMeasureSpec(width, MeasureSpec.EXACTLY)
, MeasureSpec.makeMeasureSpec(height, MeasureSpec.EXACTLY));
addView(view, 0);
return view;
}
@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
final int widthSize = MeasureSpec.getSize(widthMeasureSpec);
final int heightSize = MeasureSpec.getSize(heightMeasureSpec);
int h = 0;
if (adapter != null) {
this.rowCount = adapter.getCount();
heights = new int[rowCount];
for (int i = 0; i < heights.length; i++) {
heights[i] = adapter.getHeight(i);
}
}
//数据的高度
int tmpH = sumArray(heights, 0, heights.length);
h = Math.min(heightSize, tmpH);
setMeasuredDimension(widthSize, h);
super.onMeasure(widthMeasureSpec, heightMeasureSpec);
}
//firstIndex firstIndex+count
private int sumArray(int array[], int firstIndex, int count) {
int sum = 0;
count += firstIndex;
for (int i = firstIndex; i < count; i++) {
sum += array[i];
}
return sum;
}
@Override
public boolean onInterceptTouchEvent(MotionEvent event) {
boolean intercept = false;
switch (event.getAction()) {
case MotionEvent.ACTION_DOWN: {
currentY = (int) event.getRawY();
break;
}
case MotionEvent.ACTION_MOVE: {
int y2 = Math.abs(currentY - (int) event.getRawY());
if (y2 > touchSlop) {
intercept = true;
}
}
}
return intercept;
}
@Override
public boolean onTouchEvent(MotionEvent event) {
switch (event.getAction()) {
case MotionEvent.ACTION_MOVE: {
//移动的距离 y方向
int y2 = (int) event.getRawY();
//上滑正 下滑负
int diffY = currentY - y2;
//画布移动 并不影响子控件的位置
scrollBy(0, diffY);
}
}
return super.onTouchEvent(event);
}
private int scrollBounds(int scrollY) {
//上滑
if (scrollY > 0) {
scrollY = Math.min(scrollY, sumArray(heights, firstRow, heights.length - firstRow) - height);
} else { //下滑
//极限值 会取零 非极限值的情况下 socrlly
scrollY = Math.max(scrollY, -sumArray(heights, 0, firstRow));
}
return scrollY;
}
@Override
public void scrollBy(int x, int y) {
//scrollY表示 第一个可见Item的左上顶点 距离屏幕的左上顶点的距离
scrollY += y;
scrollY = scrollBounds(scrollY);
//scrolly
if (scrollY > 0) {
//上滑正 下滑负 边界值
while (scrollY > heights[firstRow]) {
//1 上滑移除 2 上划加载 3下滑移除 4 下滑加载
removeView(viewList.remove(0));
scrollY -= heights[firstRow];
firstRow++;
}
while (getFillHeight() < height) {
int addLast = firstRow + viewList.size();
View view = obtainView(addLast, width, heights[addLast]);
viewList.add(viewList.size(), view);
}
} else if (scrollY < 0) {
//4 下滑加载
while (scrollY < 0) {
int firstAddRow = firstRow - 1;
View view = obtainView(firstAddRow, width, heights[firstAddRow]);
viewList.add(0, view);
firstRow--;
scrollY += heights[firstRow + 1];
}
//3下滑移除
while (sumArray(heights, firstRow, viewList.size()) - scrollY - heights[firstRow + viewList.size() - 1] >= height) {
removeView(viewList.remove(viewList.size() - 1));
}
} else {
}
repositionViews();
}
private void repositionViews() {
int left, top, right, bottom, i;
top = -scrollY;
i = firstRow;
for (View view : viewList) {
bottom = top + heights[i++];
view.layout(0, top, width, bottom);
top = bottom;
}
}
private int getFillHeight() {
//数据的高度 -scrollY
return sumArray(heights, firstRow, viewList.size()) - scrollY;
}
private int getFilledHeight() {
//数据高度-scrolly
return sumArray(heights, firstRow, viewList.size()) - scrollY;
}
@Override
public void removeView(View view) {
super.removeView(view);
int key = (int) view.getTag(R.id.tag_type_view);
recycler.put(view, key);
}
interface Adapter {
View onCreateViewHodler(int position, View convertView, ViewGroup parent);
View onBinderViewHodler(int position, View convertView, ViewGroup parent);
//Item的类型
int getItemViewType(int row);
//Item的类型数量
int getViewTypeCount();
int getCount();
public int getHeight(int index);
}
}
RecyclerView recyclerView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
recyclerView = findViewById(R.id.table);
recyclerView.setAdapter(new RecyclerView.Adapter() {
@Override
public View onCreateViewHodler(int position, View convertView, ViewGroup parent) {
convertView= MainActivity.this.getLayoutInflater().inflate( R.layout.item_table,parent,false);
TextView textView= (TextView) convertView.findViewById(R.id.text1);
textView.setText("波光水门"+position);
Log.i(TAG, "onCreateViewHodler: " + convertView.hashCode());
return convertView;
}
@Override
public View onBinderViewHodler(int position, View convertView, ViewGroup parent) {
TextView textView= (TextView) convertView.findViewById(R.id.text1);
textView.setText("波光水门 "+position);
Log.i(TAG, "onBinderViewHodler: " + convertView.hashCode());
return convertView;
}
@Override
public int getItemViewType(int row) {
return 0;
}
@Override
public int getViewTypeCount() {
return 1;
}
@Override
public int getCount() {
return 30;
}
@Override
public int getHeight(int index) {
return 100;
}
});
}