Android 活用RecyclerView分割线


1、ItemDecoration简介

Recyclerview是我们日常开发中使用频率比较高的的控件,而其中的ItemDecoration作为布局装饰又能很方便的帮助我们定义分割线,列表排行效果以及设置布局悬浮置顶效果等,所以有必要去了解ItemDecoration的诸多细节。

2、基本原理

public class MyDecoration extends RecyclerView.ItemDecoration{
    /**
     * step1 相当于itemView外还有一个矩形,我们可以自由在itemview上下左右设置空余部分,
通过outRect 的left,top,right,bottom 来进行设置,我们可在这块控件进行绘制
     * 目标针对每一个item个体
     */
    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
    }

    /**
     * step2 在item间绘制  常用于绘制分割线
     * 针对整个Recyclerview 绘制需要循环遍历item子布局 然后方能针对具体的item进行增加绘制
     */
    @Override
    public void onDraw(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDraw(c, parent, state);
    }

    /**
     * 在item上绘制
     */
    @Override
    public void onDrawOver(@NonNull Canvas c, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.onDrawOver(c, parent, state);
    }
}

2.1 getItemoffsets在RecyclerView源码中作用时机

manager#getItemDecorInsetsForChild

为指定view计算分割线矩形

Rect getItemDecorInsetsForChild(View child) {
        RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams)child.getLayoutParams();
        if (!lp.mInsetsDirty) {
            return lp.mDecorInsets;
        } else if (this.mState.isPreLayout() && (lp.isItemChanged() || lp.isViewInvalid())) {
            return lp.mDecorInsets;
        } else {
            Rect insets = lp.mDecorInsets;
            insets.set(0, 0, 0, 0);
            int decorCount = this.mItemDecorations.size();

            for(int i = 0; i < decorCount; ++i) {
                this.mTempRect.set(0, 0, 0, 0);
                ((RecyclerView.ItemDecoration)this.mItemDecorations.get(i)).getItemOffsets(this.mTempRect, child, this, this.mState);
                insets.left += this.mTempRect.left;
                insets.top += this.mTempRect.top;
                insets.right += this.mTempRect.right;
                insets.bottom += this.mTempRect.bottom;
            }

            lp.mInsetsDirty = false;
            return insets;
        }
    }

        // 测量的时候 当作padding值放入其中
        public void measureChild(@NonNull View child, int widthUsed, int heightUsed) {
            RecyclerView.LayoutParams lp = (RecyclerView.LayoutParams)child.getLayoutParams();
            Rect insets = this.mRecyclerView.getItemDecorInsetsForChild(child);
            widthUsed += insets.left + insets.right;
            heightUsed += insets.top + insets.bottom;
            int widthSpec = getChildMeasureSpec(this.getWidth(), this.getWidthMode(), this.getPaddingLeft() + this.getPaddingRight() + widthUsed, lp.width, this.canScrollHorizontally());
            int heightSpec = getChildMeasureSpec(this.getHeight(), this.getHeightMode(), this.getPaddingTop() + this.getPaddingBottom() + heightUsed, lp.height, this.canScrollVertically());
            if (this.shouldMeasureChild(child, widthSpec, heightSpec, lp)) {
                child.measure(widthSpec, heightSpec);
            }

        }

manager#calculateItemDecorationsForChild

manager向外部提供的获取分割线矩形数据的api

public void calculateItemDecorationsForChild(@NonNull View child, @NonNull Rect outRect) {
            if (this.mRecyclerView == null) {
                outRect.set(0, 0, 0, 0);
            } else {
                Rect insets = this.mRecyclerView.getItemDecorInsetsForChild(child);
                outRect.set(insets);
            }
        }

可解决问题:如何获取指定itemView的分割线的高度

Rect rect = new Rect();
View view =  mRvConflict.getLayoutManager().findViewByPosition(1);
 if (view != null){
                    mRvConflict.getLayoutManager().calculateItemDecorationsForChild(view,rect);
     Log.e("decoration", "高度 = "+rect.height() );
 }

3. 分割线使用

3.1无任何分割线的RecyclerView

private void initAdapter() {
     mMyRecvAdapter = new MyRecvAdapter(mContext,mList);
     LinearLayoutManager linearLayoutManager = new LinearLayoutManager(mContext);
     linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
     mRecyclerView.setLayoutManager(linearLayoutManager);
     mRecyclerView.setAdapter(mMyRecvAdapter);
  }

相信大家对如何说些一个RecyclerView列表再熟悉不过了吧,不过推荐大家可以使用BRVAH出来蛮久的了,可以大大提升开发效率。

3.2 一行代码添加系统分割线

mRecyclerView.addItemDecoration(new DividerItemDecoration(this,DividerItemDecoration.VERTICAL));

运行效果:

分析一下: RecyclerView 为我们提供的DividerItemDecoration的用于添加分割线的类中 代码其实不多,主要是继承了ItemDecoration并实现了 getItemOffsets()和onDra()方法,这里的getItemOffsets( )实际上是在条目之间分配一块矩形区域用来放置我们的分割线,注意一下方法参数Rect outRect,而通过onDraw( )方法把条目画在刚刚申请的间隔矩形中。没错就是这么简单,有兴趣的可以对照着源码细看一下。

public class DividerItemDecoration extends RecyclerView.ItemDecoration {
    ......

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
            RecyclerView.State state) {
        if (mOrientation == VERTICAL) {
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else {
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
        // 设置矩形区域 
        // set(left,top,right,bottom) = outRect.left = left ...
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        if (parent.getLayoutManager() == null) {
            return;
        }
        if (mOrientation == VERTICAL) {
            drawVertical(c, parent);
        } else {
            drawHorizontal(c, parent);
        }
    }

   .......
}

getitemOffset可依据混排的条目数 设置间距效果

View view = null;
        GridLayoutManager.LayoutParams layoutParams = (GridLayoutManager.LayoutParams) view.getLayoutParams();
        int spanSize = layoutParams.getSpanSize();
        // 获得每行的下标 0,1
        int spanIndex = layoutParams.getSpanIndex();

3.3 不用系统的分割线,自己设定分割线的宽度和颜色

看下面只需要知己设置drawable就可以了,你想要什么形状就可以添加什么样的形状。

DividerItemDecoration dividerItemDecoration = new DividerItemDecoration(this, DividerItemDecoration.VERTICAL);
 dividerItemDecoration.setDrawable(ContextCompat.getDrawable(this,R.drawable.shape_devider_line_red));
 mRecyclerView.addItemDecoration(dividerItemDecoration);

如上右图所示

3. 4 扩展

前面已经分析了DeivderItemDecoration的实现了,我们也可以自己手动撸一个来实现不是嘛,我们可以发现前面虽然是可以设置drawable进去,那么每次还需要写一个drawable文件或者弄张.9图进去,但通常的业务环境是只需要带颜色的线条就可以了吧,所以基于此我们可以自己手写一个。

直接上代码了额:

/**
 * @author zxl on 2018/7/14.
 *         discription: 自定义分割线支持水平和垂直布局 设置默认,图片和颜色为分割线
 */

public class MyRecyclerViewDivider extends RecyclerView.ItemDecoration {
    private Paint mPaint;
    private Drawable mDivider;
    private int mDividerHeight;
    private int mOrientation;
    /**
     *  系统默认的分割线
     * */
    private static final int[] ATTRS = new int[]{android.R.attr.listDivider};

    /**
     *  设置默认的分割线
     *  @param orientation 指代分割线的方向
     * */
    public MyRecyclerViewDivider(Context context, int orientation) {
        this.mDividerHeight = 2;
        if(orientation != 1 && orientation != 0) {
            throw new IllegalArgumentException("请输入正确的参数!");
        } else {
            this.mOrientation = orientation;
            TypedArray a = context.obtainStyledAttributes(ATTRS);
            this.mDivider = a.getDrawable(0);
            a.recycle();
        }
    }

    /**
     *  设置图片资源为分割线
     * */
    public MyRecyclerViewDivider(Context context, int orientation, int drawableId) {
        this(context, orientation);
        this.mDivider = ContextCompat.getDrawable(context, drawableId);
        this.mDividerHeight = this.mDivider.getIntrinsicHeight();
    }

    /**
     *  设置线条颜色和高度给分割线
     * */
    public MyRecyclerViewDivider(Context context, int orientation, int dividerHeight, int dividerColor) {
        this(context, orientation);
        this.mDividerHeight = dividerHeight;
        this.mPaint = new Paint(1);
        this.mPaint.setColor(dividerColor);
        this.mPaint.setStyle(Paint.Style.FILL);
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);
        outRect.set(0, 0, 0, this.mDividerHeight);
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        super.onDraw(c, parent, state);
        if(this.mOrientation == 1) {
            this.drawVertical(c, parent);
        } else {
            this.drawHorizontal(c, parent);
        }
    }

    private void drawHorizontal(Canvas canvas, RecyclerView parent) {
        canvas.save();
        final  int left;
        final int right;
        // 判断RecyclerView是否要裁剪padding值
        if (parent.getClipToPadding()){
            // 需要裁剪那么就进行裁剪
            left = parent.getPaddingLeft();
            right = parent.getWidth()-parent.getPaddingRight();
            // 裁剪rv可视区域,  限制视图在该区域内是可见的,很重要的,这里
            canvas.clipRect(left,parent.getPaddingTop(),right,parent.getHeight()-parent.getPaddingBottom());
        }else {
            //  不裁剪则宽贼为rv的宽
            left = 0;
            right = parent.getWidth();
        }

        int childSize = parent.getChildCount();
        for(int i = 0; i < childSize; ++i) {
            View child = parent.getChildAt(i);
            // 获得item的信息包
            RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams)child.getLayoutParams();
            // 分割线顶部 = item的底部 + item到底部的距离 + 动画偏移
            int top = child.getBottom() + layoutParams.bottomMargin + Math.round(ViewCompat.getTranslationY(child));
            // 分割线底部 =  分割线底部 + 高度
            int bottom = top + this.mDividerHeight;
            if(this.mDivider != null) {
                this.mDivider.setBounds(left, top, right, bottom);
                this.mDivider.draw(canvas);
            }

            if(this.mPaint != null) {
                canvas.drawRect((float)left, (float)top, (float)right, (float)bottom, this.mPaint);
            }
        }
        canvas.restore();
    }

    private void drawVertical(Canvas canvas, RecyclerView parent) {
        canvas.save();
        final int top;
        final int bottom;
        if (parent.getClipToPadding()){
            top = parent.getPaddingTop();
            bottom = parent.getHeight() - parent.getPaddingBottom();
            canvas.clipRect(parent.getPaddingLeft(),top,parent.getWidth()-parent.getPaddingRight(),bottom);
        }else {
            top  = 0;
            bottom = parent.getHeight();
        }
        int childSize = parent.getChildCount();
        for(int i = 0; i < childSize; ++i) {
            View child = parent.getChildAt(i);
            RecyclerView.LayoutParams layoutParams = (RecyclerView.LayoutParams)child.getLayoutParams();
            int left = child.getRight() + layoutParams.rightMargin + Math.round(ViewCompat.getTranslationX(child));
            int right = left + this.mDividerHeight;
            if(this.mDivider != null) {
                this.mDivider.setBounds(left, top, right, bottom);
                this.mDivider.draw(canvas);
            }

            if(this.mPaint != null) {
                canvas.drawRect((float)left, (float)top, (float)right, (float)bottom, this.mPaint);
            }
        }
        canvas.restore();
    }
}

用法如下也是很简单,优点不用多说既囊括了系统提供的也支持drawable设置而且支持简易的线条颜色等,用途很大对的吧。

mRecyclerView.addItemDecoration(new MyRecyclerViewDivider(this, LinearLayoutManager.HORIZONTAL,2,ContextCompat.getColor(this,R.color.colorAccent)));

效果我下方左图所示

弄个表格出来

以下为 addItemDecoration的源码,可以发现的是可以设置多条分割线,哈哈,那么我们不就能画表格了嘛,6666

public void addItemDecoration(ItemDecoration decor, int index) {
        if (mLayout != null) {
            mLayout.assertNotInLayoutOrScroll("Cannot add item decoration during a scroll  or"
                    + " layout");
        }
        if (mItemDecorations.isEmpty()) {
            setWillNotDraw(false);
        }
        if (index < 0) {
            mItemDecorations.add(decor);
        } else {
            mItemDecorations.add(index, decor);
        }
        markItemDecorInsetsDirty();
        requestLayout();
    }

activity中的代码如下:

mMyRecvAdapter = new MyRecvAdapter(mContext,mList);
        mRecyclerView.addItemDecoration(new MyRecyclerViewDivider(this, LinearLayoutManager.HORIZONTAL,2,ContextCompat.getColor(this,R.color.colorAccent)));
        mRecyclerView.addItemDecoration(new MyRecyclerViewDivider(this,LinearLayoutManager.VERTICAL,2,ContextCompat.getColor(this,R.color.colorAccent)));
        mRecyclerView.setLayoutManager(new GridLayoutManager(this,3));
        mRecyclerView.setAdapter(mMyRecvAdapter);

原创文章,作者:ItWorker,如若转载,请注明出处:https://blog.ytso.com/291842.html

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