使用RecyclerView的几个笔记

/**
* Item spacing for custom RecyclerView
* add by xiangy
*/
public class ItemMarginDecoration extends RecyclerView.ItemDecoration {

    int itemMargin = 0;
    public ItemMarginDecoration(int itemMargin){
        this.itemMargin = itemMargin;
    }

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        outRect.left = itemMargin;
        outRect.right = itemMargin;
        outRect.bottom = itemMargin;
        outRect.top = itemMargin;
    }
}

int Margin = 0; //mRecyclerView item Margin
...
mRecyclerView.addItemDecoration(new ItemMarginDecoration(Margin));

public class TopSmoothScroller extends LinearSmoothScroller {
    TopSmoothScroller(Context context) {
        super(context);
    }


    @Override
    protected int getHorizontalSnapPreference() {
        return SNAP_TO_START;//具体见源码注释
    }


    @Override
    protected int getVerticalSnapPreference() {
        return SNAP_TO_START;//具体见源码注释
    }
}

private LinearLayoutManager Manager;
...
Manager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(mManager);
...
/**接收要跳转的位置跳转**/
public void onUpdateItem(int position) {
    LinearSmoothScroller s = new TopSmoothScroller(this);
    s.setTargetPosition(position);
    Manager.startSmoothScroll(s);
}

刷新全部可见的item，notifyDataSetChanged()
刷新指定item，notifyItemChanged(int)
从指定位置开始刷新指定个item，notifyItemRangeChanged(int,int)
插入、移动一个并自动刷新，notifyItemInserted(int)、notifyItemMoved(int)、notifyItemRemoved(int)
局部刷新，notifyItemChanged(int, Object)

public class ZoomRecycleView extends RecyclerView {

    private int mScreenWidth;
    private int mMinWidth;
    private int mMaxWidth;
    private float MIN_SCALE = 1f;
    private float MAX_SCALE = 1f;
    private int mScreenHeight;
    private static final int VELOCITY = 2500; //滑动速度

    public ZoomRecycleView(@NonNull Context context) {
        this(context, null);
    }

    public ZoomRecycleView(@NonNull Context context, @Nullable AttributeSet attrs) {
        this(context, attrs, 0);
    }

    public ZoomRecycleView(@NonNull Context context, @Nullable AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);

    }

    @Override
    public boolean fling(int velocityX, int velocityY) {
        velocityX = calcVelocity(velocityX);
        velocityY = calcVelocity(velocityY);
        return super.fling(velocityX, velocityY);
    }

    private int calcVelocity(int velocity) {
        if (velocity > 0) {
            return Math.min(velocity, VELOCITY);
        } else {
            return Math.max(velocity, -VELOCITY);
        }
    }
    @Override
    protected void onMeasure(int widthSpec, int heightSpec) {
        int width = View.MeasureSpec.getSize(widthSpec);
        int height = View.MeasureSpec.getSize(heightSpec);
        mScreenWidth = width;
        mScreenHeight = height;
        mMinWidth = (int) (mScreenWidth * 0.28f);
        mMaxWidth = mScreenWidth - 2 * mMinWidth;
        super.onMeasure(width, height);
    }

    public void setScale(float min_scale,float max_scale){
        MIN_SCALE =min_scale;
        MAX_SCALE =max_scale;
    }
    @Override
    protected void onScrollChanged(int l, int t, int oldl, int oldt) {
        super.onScrollChanged(l, t, oldl, oldt);
        final int childCount = getChildCount();
        for (int i = 0; i < childCount; i++) {
            RelativeLayout child = (RelativeLayout) getChildAt(i);
            int left = child.getLeft();
            int right = mScreenWidth - child.getRight();
            final float percent = left < 0 || right < 0 ? 0 : Math.min(left, right) * 1f / Math.max(left, right);//算出一个根据位置计算的等比函数
            float scaleFactor = MIN_SCALE + Math.abs(percent) * (MAX_SCALE - MIN_SCALE);
            child.setScaleY(scaleFactor);
            child.setScaleX(scaleFactor);
            if (percent == 1f / 1) { //在中间
                ((ImageView) child.getChildAt(0)).getDrawable().setLevel(1);
            } else {
                ((ImageView) child.getChildAt(0)).getDrawable().setLevel(0);
            }
        }
    }
}