RecyclerView添加分割线

标签：parent int 分割线添加 import android RecyclerView

RecyclerView 并没有 divider 属性，但是我们可以通过 RecyclerView 的 addItemDecoration() 来添加分割线，该方法参数为 RecyclerView.ItemDecoration。

介绍

当 RecyclerView 添加 ItemDecoration 后，RecyclerView 在绘制每个 item 的时候，会去绘制 decorator，也就是会调用 ItemDecoration 的 onDraw() 和 onDrawOver() 方法。

RecyclerView.ItemDecoration 是抽象类，主要提供三个方法：

onDraw(Canvas c, RecyclerView parent, State state)：在绘制item（drawChild）前调用
onDrawOver(Canvas c, RecyclerView parent, State state): 在绘制item（drawChild）后调用
getItemOffsets(Rect outRect, View view, RecyclerView parent, State state)：outRect设置 item 的偏移量，用于绘制 decorator（也就是divider）

关于 getItemOffsets 函数：
RecyclerView 添加分割线，实际上就是 RecyclerView 的 item 之间添加了用作分割线的View，自然而然后续的 item 就会有偏移量，所以用 getItemOffsets 中的 outRect 来保存 item 的偏移量，从而便于绘制 decorator。

实现

实际上在当前版本的 RecyclerView (25.3.1) 中已经有 ItemDecoration 关于分割线的默认实现类 DividerItemDecoration

package android.support.v7.widget;

import android.annotation.SuppressLint;
import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Rect;
import android.graphics.drawable.Drawable;
import android.support.annotation.NonNull;
import android.support.v4.view.ViewCompat;
import android.view.View;
import android.widget.LinearLayout;

public class DividerItemDecoration extends RecyclerView.ItemDecoration {
    public static final int HORIZONTAL = LinearLayout.HORIZONTAL;
    public static final int VERTICAL = LinearLayout.VERTICAL;

    // 如果不设置，则默认的分割线为 android.R.attr.listDivider 指定的 drawable
    private static final int[] ATTRS = new int[]{ android.R.attr.listDivider };

    private Drawable mDivider;

    /**
     * Current orientation. Either {@link #HORIZONTAL} or {@link #VERTICAL}.
     */
    private int mOrientation;

    private final Rect mBounds = new Rect();

    /**
     * Creates a divider {@link RecyclerView.ItemDecoration} that can be used with a
     * {@link LinearLayoutManager}.
     *
     * @param context Current context, it will be used to access resources.
     * @param orientation Divider orientation. Should be {@link #HORIZONTAL} or {@link #VERTICAL}.
     */
    public DividerItemDecoration(Context context, int orientation) {
        final TypedArray a = context.obtainStyledAttributes(ATTRS);
        mDivider = a.getDrawable(0);
        a.recycle();
        setOrientation(orientation);
    }

    /**
     * Sets the orientation for this divider. This should be called if
     * {@link RecyclerView.LayoutManager} changes orientation.
     *
     * @param orientation {@link #HORIZONTAL} or {@link #VERTICAL}
     */
    public void setOrientation(int orientation) {
        if (orientation != HORIZONTAL && orientation != VERTICAL) {
            throw new IllegalArgumentException(
                    "Invalid orientation. It should be either HORIZONTAL or VERTICAL");
        }
        mOrientation = orientation;
    }

    /**
     * Sets the {@link Drawable} for this divider.
     *
     * @param drawable Drawable that should be used as a divider.
     */
    public void setDrawable(@NonNull Drawable drawable) {
        if (drawable == null) {
            throw new IllegalArgumentException("Drawable cannot be null.");
        }
        mDivider = drawable;
    }

    @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);
        }
    }

    // 绘制 RecyclerView 为垂直布局时的分割线，此时分割线为水平分割线
    @SuppressLint("NewApi")
    private void drawVertical(Canvas canvas, RecyclerView parent) {
        canvas.save();
        final int left;
        final int right;
        // 需要考虑clipToPadding的boolean值
        if (parent.getClipToPadding()) {
            left = parent.getPaddingLeft();
            right = parent.getWidth() - parent.getPaddingRight();
            canvas.clipRect(left, parent.getPaddingTop(), right,
                    parent.getHeight() - parent.getPaddingBottom());
        } else {
            left = 0;
            right = parent.getWidth();
        }

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            parent.getDecoratedBoundsWithMargins(child, mBounds);
            final int bottom = mBounds.bottom + Math.round(ViewCompat.getTranslationY(child));
            final int top = bottom - mDivider.getIntrinsicHeight();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(canvas);
        }
        canvas.restore();
    }

    // 绘制 RecyclerView 为水平布局时的分割线，此时分割线为垂直分割线
    @SuppressLint("NewApi")
    private void drawHorizontal(Canvas canvas, RecyclerView parent) {
        canvas.save();
        final int top;
        final int bottom;
        // 需要考虑clipToPadding的boolean值
        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();
        }

        final int childCount = parent.getChildCount();
        for (int i = 0; i < childCount; i++) {
            final View child = parent.getChildAt(i);
            parent.getLayoutManager().getDecoratedBoundsWithMargins(child, mBounds);
            final int right = mBounds.right + Math.round(ViewCompat.getTranslationX(child));
            final int left = right - mDivider.getIntrinsicWidth();
            mDivider.setBounds(left, top, right, bottom);
            mDivider.draw(canvas);
        }
        canvas.restore();
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent,
            RecyclerView.State state) {
        if (mOrientation == VERTICAL) { // 垂直方向的RecyclerView, item 的 bottom 偏移量 = 分割线高度
            outRect.set(0, 0, 0, mDivider.getIntrinsicHeight());
        } else { // 水平方向的RecyclerView， item 的 right 偏移量 = 分割线宽度
            outRect.set(0, 0, mDivider.getIntrinsicWidth(), 0);
        }
    }
}

在代码中添加：

recyclerView.addItemDecoration(new DividerItemDecoration(recyclerView.getContext(), mLayoutManager.getOrientation()));

就有了分割线。默认的分割线效果是系统自带的 listDivider 的效果，我们也可以在主题配置文件中自定义全局的分割线，或者调用 setDivider 为每个 RecyclerView 设置单独的分割线。

小结

总的来说，目前添加分割线只需要使用 recyclerview-v7 包下的 DividerItemDecoration 类即可，分割线可以通过 setDivider 来个性化指定，也可以通过配置主题中的 android:listDivider 来全局指定。

例如：

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

RecyclerView添加分割线_java

这个能满足一般需求，但是如果我想使用自定义的分割线呢，看以下代码

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

RecyclerView添加分割线_android_02

package com.example.administrator.myapplication;

import android.content.ContextWrapper;
import android.os.Bundle;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.DividerItemDecoration;
import android.support.v7.widget.RecyclerView;


import java.util.List;
import java.util.ArrayList;

public class BodyActivity extends AppCompatActivity {
    RecyclerView mRecyclerView;

    @Override
    protected void onCreate(Bundle saveInstanceState) {
        super.onCreate(saveInstanceState);
        setContentView(R.layout.activity_body);
        //1.获取控件
        mRecyclerView = (RecyclerView) findViewById(R.id.recycler_view);

        //设置布局方式
        mRecyclerView.setLayoutManager(new LinearLayoutManager(this, LinearLayoutManager.VERTICAL, false));//线性布局
//        mRecyclerView.setLayoutManager(new GridLayoutManager(this,2));//网格布局
        mRecyclerView.setHasFixedSize(true); //是否重新计算大小

        //3.准备数据
        List<News> newsList = new ArrayList<>();
        News news;
        for (int i = 1; i <= 20; i++) {
            news = new News();
            news.setNewsTitle("java是世界上最好的语言" + i);
            news.setNewsSource("新华网" + i);
            news.setPublishTime("2018-8-6");
            newsList.add(news);
        }


        //添加Android自带的分割线
//      mRecyclerView.addItemDecoration(new DividerItemDecoration(this, DividerItemDecoration.VERTICAL));


        //添加自定义的分割线
        DividerItemDecoration divider = new DividerItemDecoration(this, DividerItemDecoration.VERTICAL);
        divider.setDrawable(ContextCompat.getDrawable(this, R.drawable.divider));
        mRecyclerView.addItemDecoration(divider);

        //4.准备适配器
        NewsAdapter newsAdapter = new NewsAdapter(newsList);
        mRecyclerView.setAdapter(newsAdapter);


    }
}

标签：parent,int,分割线,添加,import,android,RecyclerView
From： https://blog.51cto.com/u_4387387/6078238

介绍

实现

小结

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