Android入門之使用RecyclerView完美實現(xiàn)瀑布流界面詳解

更新時間：2023年02月22日 10:39:15 作者：TGITCIC

網(wǎng)上充滿著不完善的基于RecyclerView的瀑布流實現(xiàn)，要么根本是錯的、要么就是只知其一不知其二。本文就來用RecyclerView完美實現(xiàn)瀑布流界面，希望大家有所幫助

前言

網(wǎng)上充滿著不完善的基于RecyclerView的瀑布流實現(xiàn)，要么根本是錯的、要么就是只知其一不知其二、要么就是一充訴了一堆無用代碼、要么用的是古老的MVC設(shè)計模式。

一個真正的、用戶體驗類似于淘寶、抖音的瀑布流怎么實現(xiàn)目前基本為無解。因為本人正好自己空閑時也在做前后臺一體化開發(fā)，所以直接從本人自己項目里（mao-sir.com）公開一部分核心代碼以便于加快大家的學(xué)習(xí)進度，以使得各位不要在這種小東西上折騰太多時間。

什么是瀑布流

注意看這邊的這個布局，大家有沒有發(fā)覺這些照片分成左右、最多的還有分成三列的，但是每一行的照片、視頻、內(nèi)容的高度是“錯開”的。最早采用此布局的網(wǎng)站是Pinterest，逐漸在國內(nèi)流行開來。國內(nèi)大多數(shù)做的好的大廠的APP都是這種布局、尤以UGC（UGC它的中文意思是用戶生產(chǎn)內(nèi)容的意思，簡稱為UGC）為主的APP采用此布局最多像：知乎上的精品貼、推薦貼、小紅書種草等都是這種風(fēng)格。

瀑布流布局的優(yōu)點為：

1.吸引用戶，當(dāng)用戶在瀏覽瀑布流式布局的時候（這里拋開懶加載），用戶會產(chǎn)生一種錯覺，就是信息是不停的在更新的，這會激發(fā)用戶的好奇心，使用戶不停的往下滑動。

2.良好視覺體驗，采用瀑布流布局的方式可以打破常規(guī)網(wǎng)站布局排版，給用戶眼前一亮的新鮮感，用戶在瀏覽內(nèi)容時會感到很有新鮮感，帶來良好的視覺體驗。

3.更好的適應(yīng)移動端，由于移動設(shè)備屏幕比電腦小，一個屏幕顯示的內(nèi)容不會非常多，因此可能要經(jīng)常翻頁。而在建網(wǎng)站時使用瀑布流布局，用戶則只需要進行滾動就能夠不斷瀏覽內(nèi)容。（這一點和懶加載有一點像）

怎么實現(xiàn)瀑布流

網(wǎng)上有一些第三方控件使用了瀑布流，但是這些第三方控件都已經(jīng)廢棄或者是停更了。這些第三方控件本人都用過，不是有各種BUG就是把問題搞了很復(fù)雜。這東西其實很簡單，一天內(nèi)就可以做出生產(chǎn)級別的應(yīng)用了，哪有這么難。

難就是難在太多初學(xué)者為了趕項目或者說很多人急功近利，只想著copy paste，因此搞了一堆其實無用的代碼還把問題“混攪”了。

因此本篇會從本質(zhì)上還原最最干凈的瀑布流，同時本人會基于mvvm設(shè)計模式來講這個瀑布流。我們用的就是Android原生的控件：RecyclerView組件。下面是類淘寶、抖音用戶極致體驗的一個瀑布流“正例”（我們在文未還會給出一個體驗不好的反例供讀者對比）。

        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/rv"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
        </androidx.recyclerview.widget.RecyclerView>

下面我們來看實現(xiàn) 。

基于MVVM設(shè)計模式的RecyclerView實現(xiàn)瀑布流代碼

工程整體結(jié)構(gòu)

這是一個使用androidx的基于mvvm的工程。

至于如何把一個工程變成androidx和mvvm此處就不再贅述了，在我前面的博客中已經(jīng)寫了很詳細(xì)了。

布局

activity_main.xml布局

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools">
 
    <data>
 
    </data>
 
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:orientation="vertical"
        tools:context=".MainActivity">
 
        <androidx.recyclerview.widget.RecyclerView
            android:id="@+id/rv"
            android:layout_width="match_parent"
            android:layout_height="wrap_content">
        </androidx.recyclerview.widget.RecyclerView>
    </LinearLayout>
</layout>

瀑布流中具體的明細(xì)布局-rv_item.xml

在明細(xì)布局里，整體瀑布流墻就兩個元素，一個是照片的url另一個是文本框，實現(xiàn)很簡單。

<?xml version="1.0" encoding="utf-8"?>
<layout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto">
 
    <data>
 
        <variable
            name="item"
            type="org.mk.android.demo.demo.staggerdrecyclerview.RVBean" />
    </data>
 
    <LinearLayout
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
 
        <androidx.cardview.widget.CardView
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_margin="8dp"
            app:cardCornerRadius="8dp"
            app:cardElevation="4dp">
 
            <LinearLayout
                android:layout_width="match_parent"
                android:layout_height="wrap_content"
                android:orientation="vertical">
 
                <ImageView
                    android:id="@+id/rvImageView"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:adjustViewBounds="true"
                    android:scaleType="fitXY"
                    app:url="@{item.url}" />
 
                <TextView
                    android:id="@+id/rvTextView"
                    android:layout_width="match_parent"
                    android:layout_height="wrap_content"
                    android:textAlignment="center"
                    android:layout_margin="4dp"
                    android:text="@{item.text}" />
            </LinearLayout>
        </androidx.cardview.widget.CardView>
    </LinearLayout>
</layout>

現(xiàn)在就來看我們的代碼。

后端代碼

RVBean.java

package org.mk.android.demo.demo.staggerdrecyclerview;
 
import android.util.Log;
import android.widget.ImageView;
 
import androidx.databinding.BindingAdapter;
 
import com.bumptech.glide.Glide;
 
import java.util.Objects;
 
public class RVBean {
    private String url;
    private String text;
    private final static String TAG = "DemoStaggerdRecyclerView";
 
    @BindingAdapter("url")
    public static void loadImg(ImageView imageView, String url) {
        Glide.with(imageView).load(url).into(imageView);
    }
 
    public String getUrl() {
        return url;
    }
 
    public void setUrl(String url) {
        this.url = url;
    }
 
    public String getText() {
        return text;
    }
 
    public void setText(String text) {
        this.text = text;
    }
 
    public RVBean(String url, String text) {
        this.url = url;
        this.text = text;
    }
 
    @Override
    public boolean equals(Object o) {
        if (this == o) {
            //Log.i(TAG, ">>>>>>this==o return true");
            return true;
        }
        if (o == null || getClass() != o.getClass()) {
            //Log.i(TAG, ">>>>>>o==null||getClass()!=o.getClass() is false");
            return false;
        }
        RVBean rvBean = (RVBean) o;
        if (rvBean.url.length() != url.length() || rvBean.text.length() != text.length()) {
            //Log.i(TAG, ">>>>>>target length()!=existed url length");
            return false;
        }
        if(url.equals(rvBean.url)&&text.equals(rvBean.text)){
            //Log.i(TAG,">>>>>>url euqlas && text equals");
            return true;
        }else{
            //Log.i(TAG,">>>>>>not url euqlas && text equals");
            return false;
        }
    }
 
    @Override
    public int hashCode() {
        int hashCode = Objects.hash(url, text);
        //Log.i(TAG, ">>>>>>hashCode->" + hashCode);
        return hashCode;
    }
}

代碼中它定義了兩個元素，一個為文本框，一個為用于加載網(wǎng)絡(luò)圖片的url，網(wǎng)絡(luò)圖片我用的是我另一臺VM上的Nginx做的靜態(tài)圖片資源服務(wù)。

RVAdapter.java

package org.mk.android.demo.demo.staggerdrecyclerview;
 
import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
 
import androidx.annotation.NonNull;
import androidx.databinding.DataBindingUtil;
import androidx.recyclerview.widget.RecyclerView;
 
import com.bumptech.glide.Glide;
 
import org.mk.android.demo.demo.staggerdrecyclerview.databinding.RvItemBinding;
 
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import java.util.Locale;
 
public class RVAdapter extends RecyclerView.Adapter<RVAdapter.VH> {
    private Context context;
    private List<RVBean> rvBeans;
    private final static String TAG = "DemoStaggerdRecyclerView";
 
    public RVAdapter(Context context, List<RVBean> rvBeans) {
        this.context = context;
        this.rvBeans = rvBeans;
    }
    @Override
    public int getItemViewType(int position) {
        return position;
    }
    @NonNull
    @Override
    public VH onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
        return new VH(DataBindingUtil.inflate(
                LayoutInflater.from(context), R.layout.rv_item, parent, false).getRoot());
    }
 
    @Override
    public void onBindViewHolder(@NonNull VH holder, int position) {
        //try {
            RvItemBinding binding = DataBindingUtil.bind(holder.itemView);
            //binding.rvTextView.setText(rvBeans.get(position).getText());
            binding.setItem(rvBeans.get(position));
            /*
            //Set size
            BitmapFactory.Options options = new BitmapFactory.Options();
            options.inJustDecodeBounds = true;//這個參數(shù)設(shè)置為true才有效，
            Bitmap bmp = BitmapFactory.decodeFile(rvBeans.get(position).getUrl(), options);
            //這里的bitmap是個空
            int outHeight = options.outHeight;
            int outWidth = options.outWidth;
            Glide.with(context).load(rvBeans.get(position).getUrl()).override(outWidth,
                    outHeight).into(binding.rvImageView);
        } catch (Exception e) {
            Log.e(TAG, ">>>>>>onbindViewHolder error: " + e.getMessage(), e);
        }
             */
    }
 
    @Override
    public int getItemCount() {
        return rvBeans.size();
    }
 
    public class VH extends RecyclerView.ViewHolder {
        public VH(@NonNull View itemView) {
            super(itemView);
        }
    }
 
    //增加外部調(diào)用增加一條記錄
    public void refreshDatas(List<RVBean> datas) {
        int pc=0;
        if (datas != null && datas.size() > 0) {
            int oldSize = rvBeans.size();
            //List<RVBean> refreshedData = new ArrayList<RVBean>();
            boolean isItemExisted = false;
            for (Iterator<RVBean> newData = datas.iterator(); newData.hasNext(); ) {
                RVBean a = newData.next();
                for (Iterator<RVBean> existedData = rvBeans.iterator(); existedData.hasNext(); ) {
                    RVBean b = existedData.next();
                    if (b.equals(a)) {
                        {
                            isItemExisted = true;
                            //Log.i(TAG, b.getText() + " -> " + b.getUrl() + " is existed");
                            break;
                        }
                    }
                }
                if (!isItemExisted) {
                    pc+=1;
                    rvBeans.add(a);
                }
            }
            Log.i(TAG,">>>>>>pc->"+pc);
            if(pc>0){
                notifyItemRangeChanged(oldSize,rvBeans.size());
            }
        }
    }
}

核心代碼導(dǎo)讀

1.這個adapter用的正是mvvm設(shè)計模式做的adapter；

2.這個adapter和網(wǎng)上那些錯誤、有坑的例子最大的不同在于getItemViewType方法內(nèi)必須返回position，否則你的瀑布流在上劃加載新數(shù)據(jù)時會產(chǎn)生界面內(nèi)對照片重新進行左右切換、重排、或者把照片底部留出很大一塊空白如：左邊垂直排3張，右邊一大邊空白或者反之亦然的情況；

3.必須使用notifyItemRangeChanged來通知刷新新數(shù)據(jù)，網(wǎng)上很多例子用的是notifyDataSetChange或者是其它相關(guān)的notify，它們都是錯的，這是因為RecyclerViewer在上劃下劃時會導(dǎo)致整個瀑布流重新布局、而RecyclerView里用的是Glide異步加載網(wǎng)絡(luò)圖片的，這會導(dǎo)致組件看到有一個組片就去開始計算它的高度而實際這個照片還未加載好因此才會導(dǎo)致RecyclerView在上劃下劃時整體布局重新刷新和重布局。一定記得這個notifyItemRangeChanged，同時這個方法在使用前加載所有的圖片（list數(shù)據(jù)），傳參有兩個參數(shù)，參數(shù)1：加載新數(shù)據(jù)前原數(shù)據(jù)行.size()，參數(shù)2：新加載數(shù)據(jù).size()；

有了adapter我們來看我們的應(yīng)用了。

應(yīng)用前先別急，我們自定義了一個StaggeredGridLayoutManager。

自定義FullyStaggeredGridLayoutManager

這邊先說一下，為什么要自定義這個StaggeredGridLayoutManager？

public class FullyStaggeredGridLayoutManager extends StaggeredGridLayoutManager {

大家可以認(rèn)為，這個類是一個策略。這也是網(wǎng)上絕大部分教程根本不說的，這個策略就是從根本上避免RecyclerViewer在上劃下劃時不要進行左右切換、重新布局、圖片閃爍以及“解決Scrollview中嵌套RecyclerView實現(xiàn)瀑布流時無法顯示的問題，同時修復(fù)了子View顯示時底部多出空白區(qū)域的問題”用的，我在代碼中也做了注釋。

此處要敲一下黑板了。因此整個RecyclerView要做到類淘寶、抖音的這種用戶體驗必須是adapter里的代碼和這個自定義StaggeredGridLayoutManager結(jié)合起來才能做到。

因此我們下面就來看在MainActivity里如何把adapter結(jié)合著這個自定義的StaggeredGridLayoutManager的應(yīng)用吧。

先上我們自定義的這個StaggeredGridLayoutManager-我們在此把它命名叫做：FullyStaggeredGridLayoutManager的全代碼。

FullyStaggeredGridLayoutManager.java代碼

package org.mk.android.demo.demo.staggerdrecyclerview;
 
import android.content.Context;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.util.Log;
import android.view.View;
 
import androidx.recyclerview.widget.RecyclerView;
import androidx.recyclerview.widget.StaggeredGridLayoutManager;
 
 
import java.lang.reflect.Field;
 
/**
 * @descride 解決Scrollview中嵌套RecyclerView實現(xiàn)瀑布流時無法顯示的問題，同時修復(fù)了子View顯示時底部多出空白區(qū)域的問題
 */
public class FullyStaggeredGridLayoutManager extends StaggeredGridLayoutManager {
    private static boolean canMakeInsetsDirty = true;
    private static Field insetsDirtyField = null;
 
    private static final int CHILD_WIDTH = 0;
    private static final int CHILD_HEIGHT = 1;
    private static final int DEFAULT_CHILD_SIZE = 100;
    private int spanCount = 0;
 
    private final int[] childDimensions = new int[2];
    private int[] childColumnDimensions;
 
    private int childSize = DEFAULT_CHILD_SIZE;
    private boolean hasChildSize;
    private final Rect tmpRect = new Rect();
 
    public FullyStaggeredGridLayoutManager(Context context, AttributeSet attrs, int defStyleAttr,
                                           int defStyleRes) {
        super(context, attrs, defStyleAttr, defStyleRes);
    }
 
    public FullyStaggeredGridLayoutManager(int spanCount, int orientation) {
        super(spanCount, orientation);
        this.spanCount = spanCount;
    }
 
    public static int makeUnspecifiedSpec() {
        return View.MeasureSpec.makeMeasureSpec(0, View.MeasureSpec.UNSPECIFIED);
    }
 
    @Override
    public void onMeasure(RecyclerView.Recycler recycler, RecyclerView.State state, int widthSpec,
                          int heightSpec) {
        final int widthMode = View.MeasureSpec.getMode(widthSpec);
        final int heightMode = View.MeasureSpec.getMode(heightSpec);
 
        final int widthSize = View.MeasureSpec.getSize(widthSpec);
        final int heightSize = View.MeasureSpec.getSize(heightSpec);
 
        final boolean hasWidthSize = widthMode != View.MeasureSpec.UNSPECIFIED;
        final boolean hasHeightSize = heightMode != View.MeasureSpec.UNSPECIFIED;
 
        final boolean exactWidth = widthMode == View.MeasureSpec.EXACTLY;
        final boolean exactHeight = heightMode == View.MeasureSpec.EXACTLY;
 
        final int unspecified = makeUnspecifiedSpec();
 
        if (exactWidth && exactHeight) {
            // in case of exact calculations for both dimensions let's use default "onMeasure" implementation
            super.onMeasure(recycler, state, widthSpec, heightSpec);
            return;
        }
 
        final boolean vertical = getOrientation() == VERTICAL;
 
        initChildDimensions(widthSize, heightSize, vertical);
 
        int width = 0;
        int height = 0;
 
        // it's possible to get scrap views in recycler which are bound to old (invalid) adapter entities. This
        // happens because their invalidation happens after "onMeasure" method. As a workaround let's clear the
        // recycler now (it should not cause any performance issues while scrolling as "onMeasure" is never
        // called whiles scrolling)
        recycler.clear();
 
        final int stateItemCount = state.getItemCount();
        final int adapterItemCount = getItemCount();
 
        childColumnDimensions = new int[adapterItemCount];
        // adapter always contains actual data while state might contain old data (f.e. data before the animation is
        // done). As we want to measure the view with actual data we must use data from the adapter and not from  the
        // state
        for (int i = 0; i < adapterItemCount; i++) {
            if (vertical) {
                if (!hasChildSize) {
                    if (i < stateItemCount) {
                        // we should not exceed state count, otherwise we'll get IndexOutOfBoundsException. For such items
                        // we will use previously calculated dimensions
                        measureChild(recycler, i, widthSize, unspecified, childDimensions);
                    } else {
                        logMeasureWarning(i);
                    }
                }
                childColumnDimensions[i] = childDimensions[CHILD_HEIGHT];
                //height += childDimensions[CHILD_HEIGHT];
                if (i == 0) {
                    width = childDimensions[CHILD_WIDTH];
                }
                if (hasHeightSize && height >= heightSize) {
                    break;
                }
            } else {
                if (!hasChildSize) {
                    if (i < stateItemCount) {
                        // we should not exceed state count, otherwise we'll get IndexOutOfBoundsException. For such items
                        // we will use previously calculated dimensions
                        measureChild(recycler, i, unspecified, heightSize, childDimensions);
                    } else {
                        logMeasureWarning(i);
                    }
                }
                width += childDimensions[CHILD_WIDTH];
                if (i == 0) {
                    height = childDimensions[CHILD_HEIGHT];
                }
                if (hasWidthSize && width >= widthSize) {
                    break;
                }
            }
        }
 
        int[] maxHeight = new int[spanCount];
        for (int i = 0; i < adapterItemCount; i++) {
            int position = i % spanCount;
            if (i < spanCount) {
                maxHeight[position] += childColumnDimensions[i];
            } else if (position < spanCount) {
                int mixHeight = maxHeight[0];
                int mixPosition = 0;
                for (int j = 0; j < spanCount; j++) {
                    if (mixHeight > maxHeight[j]) {
                        mixHeight = maxHeight[j];
                        mixPosition = j;
                    }
                }
                maxHeight[mixPosition] += childColumnDimensions[i];
            }
        }
 
        for (int i = 0; i < spanCount; i++) {
            for (int j = 0; j < spanCount - i - 1; j++) {
                if (maxHeight[j] < maxHeight[j + 1]) {
                    int temp = maxHeight[j];
                    maxHeight[j] = maxHeight[j + 1];
                    maxHeight[j + 1] = temp;
                }
            }
        }
        height = maxHeight[0];//this is max height
 
        if (exactWidth) {
            width = widthSize;
        } else {
            width += getPaddingLeft() + getPaddingRight();
            if (hasWidthSize) {
                width = Math.min(width, widthSize);
            }
        }
 
        if (exactHeight) {
            height = heightSize;
        } else {
            height += getPaddingTop() + getPaddingBottom();
            if (hasHeightSize) {
                height = Math.min(height, heightSize);
            }
        }
 
        setMeasuredDimension(width, height);
    }
 
    private void logMeasureWarning(int child) {
        if (BuildConfig.DEBUG) {
            Log.w("LinearLayoutManager", "Can't measure child #"
                    + child
                    + ", previously used dimensions will be reused."
                    + "To remove this message either use #setChildSize() method or don't run RecyclerView animations");
        }
    }
 
    private void initChildDimensions(int width, int height, boolean vertical) {
        if (childDimensions[CHILD_WIDTH] != 0 || childDimensions[CHILD_HEIGHT] != 0) {
            // already initialized, skipping
            return;
        }
        if (vertical) {
            childDimensions[CHILD_WIDTH] = width;
            childDimensions[CHILD_HEIGHT] = childSize;
        } else {
            childDimensions[CHILD_WIDTH] = childSize;
            childDimensions[CHILD_HEIGHT] = height;
        }
    }
 
    @Override public void setOrientation(int orientation) {
        // might be called before the constructor of this class is called
        //noinspection ConstantConditions
        if (childDimensions != null) {
            if (getOrientation() != orientation) {
                childDimensions[CHILD_WIDTH] = 0;
                childDimensions[CHILD_HEIGHT] = 0;
            }
        }
        super.setOrientation(orientation);
    }
 
    public void clearChildSize() {
        hasChildSize = false;
        setChildSize(DEFAULT_CHILD_SIZE);
    }
 
    public void setChildSize(int childSize) {
        hasChildSize = true;
        if (this.childSize != childSize) {
            this.childSize = childSize;
            requestLayout();
        }
    }
 
    private void measureChild(RecyclerView.Recycler recycler, int position, int widthSize,
                              int heightSize, int[] dimensions) {
        final View child;
        try {
            child = recycler.getViewForPosition(position);
        } catch (IndexOutOfBoundsException e) {
            if (BuildConfig.DEBUG) {
                Log.w("LinearLayoutManager",
                        "LinearLayoutManager doesn't work well with animations. Consider switching them off",
                        e);
            }
            return;
        }
 
        final RecyclerView.LayoutParams p = (RecyclerView.LayoutParams) child.getLayoutParams();
 
        final int hPadding = getPaddingLeft() + getPaddingRight();
        final int vPadding = getPaddingTop() + getPaddingBottom();
 
        final int hMargin = p.leftMargin + p.rightMargin;
        final int vMargin = p.topMargin + p.bottomMargin;
 
        // we must make insets dirty in order calculateItemDecorationsForChild to work
        makeInsetsDirty(p);
        // this method should be called before any getXxxDecorationXxx() methods
        calculateItemDecorationsForChild(child, tmpRect);
 
        final int hDecoration = getRightDecorationWidth(child) + getLeftDecorationWidth(child);
        final int vDecoration = getTopDecorationHeight(child) + getBottomDecorationHeight(child);
 
        final int childWidthSpec =
                getChildMeasureSpec(widthSize, hPadding + hMargin + hDecoration, p.width,
                        canScrollHorizontally());
        final int childHeightSpec =
                getChildMeasureSpec(heightSize, vPadding + vMargin + vDecoration, p.height,
                        canScrollVertically());
 
        child.measure(childWidthSpec, childHeightSpec);
 
        dimensions[CHILD_WIDTH] = getDecoratedMeasuredWidth(child) + p.leftMargin + p.rightMargin;
        dimensions[CHILD_HEIGHT] = getDecoratedMeasuredHeight(child) + p.bottomMargin + p.topMargin;
 
        // as view is recycled let's not keep old measured values
        makeInsetsDirty(p);
        recycler.recycleView(child);
    }
 
    private static void makeInsetsDirty(RecyclerView.LayoutParams p) {
        if (!canMakeInsetsDirty) {
            return;
        }
        try {
            if (insetsDirtyField == null) {
                insetsDirtyField = RecyclerView.LayoutParams.class.getDeclaredField("mInsetsDirty");
                insetsDirtyField.setAccessible(true);
            }
            insetsDirtyField.set(p, true);
        } catch (NoSuchFieldException e) {
            onMakeInsertDirtyFailed();
        } catch (IllegalAccessException e) {
            onMakeInsertDirtyFailed();
        }
    }
 
    private static void onMakeInsertDirtyFailed() {
        canMakeInsetsDirty = false;
        if (BuildConfig.DEBUG) {
            Log.w("LinearLayoutManager",
                    "Can't make LayoutParams insets dirty, decorations measurements might be incorrect");
        }
    }
}

MainActivity.java

從這兒開始我們要進入正題了，這邊要說真正的RecyclerView的應(yīng)用了。

在此演示代碼塊里為了同時便于初學(xué)者和正在尋找RecyclerView上劃下劃時錯位過大、重新布局影響體驗的老手同時閱讀和查詢問題時方便，我要說一下整個Demo代碼運行的設(shè)計思路如下：

1.上手先加載12條數(shù)據(jù)；

2.對上劃（手指按住屏幕向上拉），一直拉、拉、拉，拉到第12條，觸發(fā)了RecyclerView的onScrollStateChanged中的“往上拉拉不動”事件后開始再加載6條數(shù)據(jù)，以模擬實際項目中的“翻頁時走一下后臺API取新數(shù)據(jù)”的過程；

package org.mk.android.demo.demo.staggerdrecyclerview;
 
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.databinding.DataBindingUtil;
import androidx.recyclerview.widget.DefaultItemAnimator;
import androidx.recyclerview.widget.RecyclerView;
import androidx.recyclerview.widget.SimpleItemAnimator;
import androidx.recyclerview.widget.StaggeredGridLayoutManager;
 
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
 
import org.mk.android.demo.demo.staggerdrecyclerview.databinding.ActivityMainBinding;
 
import java.util.ArrayList;
import java.util.List;
 
public class MainActivity extends AppCompatActivity {
    private ActivityMainBinding binding;
    private List<RVBean> rvBeanList = new ArrayList<>();
    private RVAdapter adapter;
    private final static String TAG = "DemoStaggerdRecyclerView";
    private final static String CDN_URL="http://172.16.4.249/mkcdn";
    private FullyStaggeredGridLayoutManager slm=null;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        binding = DataBindingUtil.inflate(LayoutInflater.from(this), R.layout.activity_main, null, false);
        setContentView(binding.getRoot());
        slm=new FullyStaggeredGridLayoutManager(2,
                FullyStaggeredGridLayoutManager.VERTICAL);
 
        binding.rv.setLayoutManager(slm);
 
        ((SimpleItemAnimator)binding.rv.getItemAnimator()).setSupportsChangeAnimations(false);
        ((DefaultItemAnimator) binding.rv.getItemAnimator()).setSupportsChangeAnimations(false);
 
        binding.rv.getItemAnimator().setChangeDuration(0);
        binding.rv.setHasFixedSize(true);
        initData();
 
    }
 
    private void initData() {
 
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_13.jpeg", "1"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_14.jpeg", "2"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_15.jpeg", "3"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_16.jpeg", "4"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_17.jpeg", "5"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_18.jpeg", "6"));
        rvBeanList.add(new RVBean(CDN_URL+"img/recommend/recom_19.jpeg", "7"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_20.jpeg", "8"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_21.jpeg", "9"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_22.jpeg", "10"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_23.jpeg", "11"));
        rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_24.jpeg", "12"));
        adapter = new RVAdapter(this, rvBeanList);
        //主要就是這個LayoutManager，就是用這個來實現(xiàn)瀑布流的，2表示有2列(垂直)或3行(水平)，我們這里用的垂直VERTICAL
 
        //binding.rv.addItemDecoration(new SpaceItemDecoration(2, 20));
 
 
        binding.rv.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(@NonNull RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                if (!recyclerView.canScrollVertically(1) && newState == RecyclerView.SCROLL_STATE_IDLE) {
                    Log.i(TAG, "上拉拉不動時觸發(fā)加載新數(shù)據(jù)");
                    rvBeanList = new ArrayList<>();
                    rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_25.jpeg", "13"));
                    rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_26.jpeg", "14"));
                    rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_27.jpeg", "15"));
                    rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_28.jpeg", "16"));
                    rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_29.jpeg", "17"));
                    rvBeanList.add(new RVBean(CDN_URL+"/img/recommend/recom_30.jpeg", "18"));
                    adapter.refreshDatas(rvBeanList);
                }
                if (!recyclerView.canScrollVertically(-1) && newState == RecyclerView.SCROLL_STATE_IDLE) {
                    Log.i(TAG, "下拉拉不動時觸發(fā)加載新數(shù)據(jù)");
                }
            }
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                slm.invalidateSpanAssignments();//防止第一行到頂部有空白
            }
        });
        //((SimpleItemAnimator)RecyclerView.getItemAnimator()).setSupportsChangeAnimations(false);
        binding.rv.setAdapter(adapter);
    }
}

核心代碼導(dǎo)讀：

以下這一陀就是我說的使用自定義的StaggeredGridLayoutManager+adapter中的事件覆蓋一起實現(xiàn)了著名的RecyclerView上劃下劃時重新布局、翻頁的梗。

同時，一定要記得覆蓋RecyclerView的onScrolled事件，在事件中加入這樣的代碼

@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
     super.onScrolled(recyclerView, dx, dy);
     slm.invalidateSpanAssignments();//防止第一行到頂部有空白
}

總結(jié)

正確的做法

因此這邊總結(jié)一下共有5個點，做到這5個點才能真正避免網(wǎng)上一堆的關(guān)于RecyclerView快速上劃下劃時整個界面產(chǎn)生了春左右列切換、重新布局、布局不合理如：左邊垂直排了3-4個圖片而把右邊留出一大塊空白的梗的綜合手段：

1.必須使用一個自定義的StaggeredGridLayoutManager，你可以直接使用我博客中的代碼，它來自于我正在制作的上生產(chǎn)的mao-sir.com的app中的代碼，這是我的個人的一個開源中臺產(chǎn)品；

2.必須要設(shè)置上面代碼截圖中的4個屬性即：

SimpleItemAnimator里的setSupportsChangeAnimations(false);
DefaultItemAnimator里的setSupportsChangeAnimations(false);
setChangeDuration(0);
setHasFixedSize(true);

3.必須要覆蓋RecyclerView的onScrolled方法，在方法里設(shè)置防止第一行到頂部有空白的操作；

4.必須要在adapter里覆蓋getItemViewType，在方法內(nèi)返回position；

5.必須要在adapter里刷新數(shù)據(jù)時使用：notifyItemRangeChanged；