RecycleView学习3 ItemDecoration 自定义

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RecycleView ItemDecoration设置RecycleView 间隔，设置方式RecycleView.addItemDecoration();

public class DividedLinerDecorator extends RecyclerView.ItemDecoration {
    private Paint mPaint;
    private Drawable mDivider;
    private int mDividerHeight = 1;
    private int mOrientation;
    private static final int[] ATTRS = new int[]{android.R.attr.listDivider};

    public DividedLinerDecorator(Context context, int orientation) {
        if (orientation != LinearLayoutManager.VERTICAL && orientation != LinearLayoutManager.HORIZONTAL) {
            throw new IllegalArgumentException("");
        }
        mOrientation = orientation;

        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        mDivider = a.getDrawable(0);
        a.recycle();
    }

    public DividedLinerDecorator(Context context, int orientation, int drawableId) {
        this(context, orientation);
        mDivider = ContextCompat.getDrawable(context, drawableId);
        mDividerHeight = mDivider.getIntrinsicHeight();
    }

    public DividedLinerDecorator(Context context, int orientation, int dividerHeight, int dividerColor) {
        this(context, orientation);
        mDividerHeight = dividerHeight;
        mPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mPaint.setColor(dividerColor);
        mPaint.setStyle(Paint.Style.FILL);
    }

	//设置上下左右间距
    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        if (mOrientation == LinearLayoutManager.HORIZONTAL){
            outRect.set(0, 0, 0, mDividerHeight);
        }else{
            outRect.set(0, 0, mDividerHeight, 0);
        }
    }

//绘制间隔
    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        if (mOrientation == LinearLayoutManager.VERTICAL) {
            drawVertical(c, parent);
        } else {
            drawHorizontal(c, parent);
        }
    }

    private void drawHorizontal(Canvas canvas, RecyclerView parent) {
        final int left = parent.getPaddingLeft();
        final int right = parent.getMeasuredWidth() - parent.getPaddingRight();
        final int childSize = parent.getChildCount();
        for (int i = 0; i < childSize - 1; i++) {
            final View child = parent.getChildAt(i);
            RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
            final int top = child.getBottom() + layoutParams.bottomMargin;
            final int bottom = top + mDividerHeight;
            if (mDivider != null) {
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(canvas);
            }
            if (mPaint != null) {
                canvas.drawRect(left, top, right, bottom, mPaint);
            }
        }
    }

    private void drawVertical(Canvas canvas, RecyclerView parent) {
        final int top = parent.getPaddingTop();
        final int bottom = parent.getMeasuredHeight() - parent.getPaddingBottom();
        final int childSize = parent.getChildCount();
        for (int i = 0; i < childSize - 1; i++) {
            final View child = parent.getChildAt(i);
            RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams) child.getLayoutParams();
            final int left = child.getRight() + layoutParams.rightMargin;
            final int right = left + mDividerHeight;
            if (mDivider != null) {
                mDivider.setBounds(left, top, right, bottom);
                mDivider.draw(canvas);
            }
            if (mPaint != null) {
                canvas.drawRect(left, top, right, bottom, mPaint);
            }
        }
    }
}

getItemOffsets 中设置上下左右的边界：

@Override
    public void getItemOffsets( Rect outRect, View view,
                                RecyclerView parent, RecyclerView.State state ) {

        if ( portrait ) {
            if ( parent.getChildPosition( view ) == 0 )
                outRect.top = space;
            outRect.bottom = space;
        } else {
            if ( parent.getChildPosition( view ) == 0 )
                outRect.left = space;
            outRect.right = space;
        }
    }

onDraw 可以不重写，按照默认绘制方式，重写之后可以绘制成任意样式。