Use ViewGroup to implement RecyclerView

Use ViewGroup to implement RecyclerView

Recyclerview is now gradually replacing listview. This control is very handsome and much more powerful than listview. Here we don’t want to discuss how to use it. Here I think we can customize a ViewGroup to implement RecyclerView. Stop talking nonsense, direct code:

package com.example.skateboard.myapplication;

import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.support.v4.widget.EdgeEffectCompat;
import android.util.AttributeSet;
import android.view.MotionEvent;
import android.view.View;
import android.view.ViewGroup;
import android.widget.Scroller;

import java.util.HashMap;

/**
 * Created by skateboard on 16-3-8.
 */
public class FinalViewPagaIndicator extends ViewGroup {
    
    

    private EdgeEffectCompat leftEdge;//用来展示滑动到边界，这个以后再说

    private EdgeEffectCompat rightEdge;

    private Scroller scroller;

    private ViewPageIndicatorAdapter adapter;

    private HashMap<Integer, FinalIndicatorViewHolder> viewPos = new HashMap<>();

    private int screenWidth;

    private int itemWidth;

    private int itemHeight;

    private int oneScreenItemNumber;

    private int willShowNumber;

    private int curIndex;

    private int firstIndex;

    private int childCount;

    private float touchX;

    private int touchScrollX;

    private boolean hasAdapter;


    public FinalViewPagaIndicator(Context context) {
        super(context);
        init(context);
    }

    public FinalViewPagaIndicator(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context);
    }

    public FinalViewPagaIndicator(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context);
    }

    private void init(Context context) {
        calculateScreenWidth(context);
        initEdge(context);

    }
//计算屏幕大小
    private int calculateScreenWidth(Context context) {
        screenWidth = context.getResources().getDisplayMetrics().widthPixels;
        return screenWidth;
    }

    private void initScroller(Context context) {
        scroller = new Scroller(context);
    }

    private void initEdge(Context context) {
        leftEdge = new EdgeEffectCompat(context);
        rightEdge = new EdgeEffectCompat(context);
    }

    public void setAdapter(ViewPageIndicatorAdapter adapter) {
        this.adapter = adapter;
        postInvalidate();
        scrollTo(300,0);
        scrollTo(0,0);
    }


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


    private void firstSetAdapter(int widthMeasureSpec, int heightMeasureSpec)
    {
        calculateItemNumber(widthMeasureSpec, heightMeasureSpec);
        addAdapterViews();
        hasAdapter=true;
    }

    private void addAdapterViews() {
        if(adapter!=null && !hasAdapter)
        {
            viewPos.clear();
            for (int i = 0; i < willShowNumber; i++) {
                FinalIndicatorViewHolder itemViewHolder = adapter.onCreateViewHolder(this);
                addView(itemViewHolder.itemView);
                adapter.onBindViewHolder(itemViewHolder, i);
                viewPos.put(i, itemViewHolder);
            }
            childCount = getChildCount();
        }
    }

//计算一屏能容纳几个item（做多容纳的item+2）
    private void calculateItemNumber(int widthMeasureSpec, int heightMeasureSpec) {
        if (adapter != null && !hasAdapter) {
            FinalIndicatorViewHolder viewHolder = adapter.onCreateViewHolder(this);
            View itemView = viewHolder.itemView;
            this.addView(itemView);
            measureChild(itemView, widthMeasureSpec, heightMeasureSpec);
            itemWidth = itemView.getMeasuredWidth();
            itemHeight = itemView.getMeasuredHeight();
            oneScreenItemNumber = screenWidth / itemWidth + 2;
            int adapterItemCount = adapter.getItemCount();
            if (adapterItemCount > oneScreenItemNumber) {
                willShowNumber = oneScreenItemNumber;
            } else {
                willShowNumber = adapterItemCount;
            }
            curIndex=willShowNumber-1;
            firstIndex=0;
            removeAllViews();
        }

    }

    @Override
    protected void onLayout(boolean changed, int l, int t, int r, int b) {
        int curLeft = 0;
        for (int i = 0; i < willShowNumber; i++) {
            View item = getChildAt(i);
            item.layout(curLeft, 0, curLeft + item.getMeasuredWidth(), item.getMeasuredHeight());
            curLeft += item.getMeasuredWidth();
        }
    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        switch (event.getAction()) {
            case MotionEvent.ACTION_DOWN:
                touchX = event.getX();
                touchScrollX = getScrollX();
                break;
            case MotionEvent.ACTION_MOVE:
                float movX = event.getX();
                float changeX = movX - touchX;
//                if(firstIndex==0 && changeX>0)
//                {
    
    
//                    return true;
//                }
//                else if(curIndex==adapter.getItemCount()-1 && changeX<0)
//                {
    
    
//                    return true;
//                }
                if (getScrollX()>= itemWidth && changeX<0) {
                    loadNext();
                } else if (getScrollX() <= 0 && changeX>0) {
                    loadPre();
                }
                else
                {
                    scrollBy(-(int) changeX, 0);
                }
                touchX = event.getX();
                break;
        }
        return true;
    }

//加载下一个item
    private void loadNext() {

        if (curIndex >= (adapter.getItemCount() - 1)) {
            return;
        }
        scrollTo(0,0);
        postInvalidate();
        ++curIndex;
        FinalIndicatorViewHolder itemViewHolder=viewPos.get(firstIndex);
        View itemView=itemViewHolder.itemView;
        removeView(itemView);
        adapter.onBindViewHolder(itemViewHolder,curIndex);
        addView(itemView);




        viewPos.put(curIndex,itemViewHolder);

        viewPos.remove(firstIndex);
        ++firstIndex;

    }

//加载前一个item
    private void loadPre() {
        if (firstIndex <=0) {
            return;
        }

        firstIndex--;
        FinalIndicatorViewHolder itemViewHolder=viewPos.get(curIndex);
        View itemView=itemViewHolder.itemView;
        removeView(itemView);
        adapter.onBindViewHolder(itemViewHolder,firstIndex);
        scrollTo(itemWidth,0);
        addView(itemView,0);
        viewPos.put(firstIndex,itemViewHolder);
        viewPos.remove(curIndex);
        curIndex--;
    }

    @Override
    public void computeScroll() {
        super.computeScroll();
        if (scroller.computeScrollOffset()) {
            scrollTo(scroller.getCurrX(), scroller.getCurrY());
            postInvalidate();
        }
    }

    public static class ViewPageIndicatorAdapter {
    
    
        public int getItemCount() {
            return 0;
        }

        public FinalIndicatorViewHolder onCreateViewHolder(ViewGroup parent) {
            return null;
        }

        public void onBindViewHolder(FinalIndicatorViewHolder holder, int position) {

        }

    }

    public static class FinalIndicatorViewHolder {
    
    
        public View itemView;

        public FinalIndicatorViewHolder(View view) {
            this.itemView = view;
        }
    }

//    @Override
//    protected void dispatchDraw(Canvas canvas) {
    
    
//        int state=canvas.save();
//        canvas.translate(getScrollX(),0);
//        super.dispatchDraw(canvas);
//        canvas.restoreToCount(state);
//    }

}