Android UI 之WaterFall瀑布流效果

    所谓瀑布流效果，简单说就是宽度相同但是高度不同的一大堆图片，分成几列，然后像水流一样向下排列，并随着用户的上下滑动自动加载更多的图片内容。

    语言描述比较抽象，具体效果看下面的截图：

       

    其实这个效果在web上应用的还蛮多的，在android上也有一些应用有用到。因为看起来参差不齐，所以比较有新鲜感，不像传统的九宫格那样千篇一律。

    网络上相关的文章也有几篇，但是整理后发现要么忽略了OOM的处理，要么代码的逻辑相对来说有一点混乱，滑动效果也有一点卡顿。

    所以后来自己干脆换了一下思路，重新实现了这样一个瀑布流效果。目前做的测试不多，但是加载几千张图片还没有出现过OOM的情况，滑动也比较流畅。

    本文原创，如需转载，请注明转载地址：http://blog.csdn.net/carrey1989/article/details/10950673

    下面大体讲解一下实现思路。

    要想比较好的实现这个效果主要有两个重点：

    一是在用户滑动到底部的时候加载下一组图片内容的处理。

    二是当加载图片比较多的情况下，对图片进行回收，防止OOM的处理。

    对于第一点，主要是加载时机的判断以及加载内容的异步处理。这一部分其实理解起来还是比较容易，具体可以参见下面给出的源码。

    对于第二点，在进行回收的时候，我们的整体思路是以用户当前看到的这一个屏幕为基准，向上两屏以及向下两屏一共有5屏的内容，超出这5屏范围的bitmap将被回收。

    在向上滚动的时候，将回收超过下方两屏范围的bitmap，并重载进入上方两屏的bitmap。

    在向下滚动的时候，将回收超过上方两屏范围的bitmap，并重载进入下方两屏的bitmap。

    具体的实现思路还是参见源码，我有给出比较详细的注释。

先来看一下项目的结构：

WaterFall.java

package com.carrey.waterfall.waterfall;import java.io.IOException;import java.lang.ref.WeakReference;import java.util.ArrayList;import java.util.Random;import android.content.Context;import android.graphics.Color;import android.os.Handler;import android.os.Message;import android.util.AttributeSet;import android.view.MotionEvent;import android.widget.LinearLayout;import android.widget.ScrollView;/** * 瀑布流 * 某些参数做了固定设置，如果想扩展功能，可自行修改 * @author carrey * */public class WaterFall extends ScrollView {/** 延迟发送message的handler */private DelayHandler delayHandler;/** 添加单元到瀑布流中的Handler */private AddItemHandler addItemHandler;/** ScrollView直接包裹的LinearLayout */private LinearLayout containerLayout;/** 存放所有的列Layout */private ArrayList<LinearLayout> colLayoutArray;/** 当前所处的页面（已经加载了几次） */private int currentPage;/** 存储每一列中向上方向的未被回收bitmap的单元的最小行号 */private int[] currentTopLineIndex;/** 存储每一列中向下方向的未被回收bitmap的单元的最大行号 */private int[] currentBomLineIndex;/** 存储每一列中已经加载的最下方的单元的行号 */private int[] bomLineIndex;/** 存储每一列的高度 */private int[] colHeight;/** 所有的图片资源路径 */private String[] imageFilePaths;/** 瀑布流显示的列数 */private int colCount;/** 瀑布流每一次加载的单元数量 */private int pageCount;/** 瀑布流容纳量 */private int capacity;private Random random;/** 列的宽度 */private int colWidth;private boolean isFirstPage;public WaterFall(Context context, AttributeSet attrs, int defStyle) {super(context, attrs, defStyle);init();}public WaterFall(Context context, AttributeSet attrs) {super(context, attrs);init();}public WaterFall(Context context) {super(context);init();}/** 基本初始化工作 */private void init() {delayHandler = new DelayHandler(this);addItemHandler = new AddItemHandler(this);colCount = 4;//默认情况下是4列pageCount = 30;//默认每次加载30个瀑布流单元capacity = 10000;//默认容纳10000张图random = new Random();colWidth = getResources().getDisplayMetrics().widthPixels / colCount;colHeight = new int[colCount];currentTopLineIndex = new int[colCount];currentBomLineIndex = new int[colCount];bomLineIndex = new int[colCount];colLayoutArray = new ArrayList<LinearLayout>();}/** * 在外部调用 第一次装载页面 必须调用 */public void setup() {containerLayout = new LinearLayout(getContext());containerLayout.setBackgroundColor(Color.WHITE);LinearLayout.LayoutParams layoutParams = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.MATCH_PARENT);addView(containerLayout, layoutParams);for (int i = 0; i < colCount; i++) {LinearLayout colLayout = new LinearLayout(getContext());LinearLayout.LayoutParams colLayoutParams = new LinearLayout.LayoutParams(colWidth, LinearLayout.LayoutParams.WRAP_CONTENT);colLayout.setPadding(2, 2, 2, 2);colLayout.setOrientation(LinearLayout.VERTICAL);containerLayout.addView(colLayout, colLayoutParams);colLayoutArray.add(colLayout);}try {imageFilePaths = getContext().getAssets().list("images");} catch (IOException e) {e.printStackTrace();}//添加第一页addNextPageContent(true);}@Overridepublic boolean onTouchEvent(MotionEvent ev) {switch (ev.getAction()) {case MotionEvent.ACTION_DOWN:break;case MotionEvent.ACTION_UP://手指离开屏幕的时候向DelayHandler延时发送一个信息，然后DelayHandler//届时来判断当前的滑动位置，进行不同的处理。delayHandler.sendMessageDelayed(delayHandler.obtainMessage(), 200);break;}return super.onTouchEvent(ev);}@Overrideprotected void onScrollChanged(int l, int t, int oldl, int oldt) {//在滚动过程中，回收滚动了很远的bitmap,防止OOM/*---回收算法说明： * 回收的整体思路是： * 我们只保持当前手机显示的这一屏以及上方两屏和下方两屏 一共5屏内容的Bitmap, * 超出这个范围的单元Bitmap都被回收。 * 这其中又包括了一种情况就是之前回收过的单元的重新加载。 * 详细的讲解： * 向下滚动的时候：回收超过上方两屏的单元Bitmap,重载进入下方两屏以内Bitmap * 向上滚动的时候：回收超过下方两屏的单元bitmao,重载进入上方两屏以内bitmap * ---*/int viewHeight = getHeight();if (t > oldt) {//向下滚动if (t > 2 * viewHeight) {for (int i = 0; i < colCount; i++) {LinearLayout colLayout = colLayoutArray.get(i);//回收上方超过两屏bitmapFlowingView topItem = (FlowingView) colLayout.getChildAt(currentTopLineIndex[i]);if (topItem.getFootHeight() < t - 2 * viewHeight) {topItem.recycle();currentTopLineIndex[i] ++;}//重载下方进入(+1)两屏以内bitmapFlowingView bomItem = (FlowingView) colLayout.getChildAt(Math.min(currentBomLineIndex[i] + 1, bomLineIndex[i]));if (bomItem.getFootHeight() <= t + 3 * viewHeight) {bomItem.reload();currentBomLineIndex[i] = Math.min(currentBomLineIndex[i] + 1, bomLineIndex[i]);}}}} else {//向上滚动for (int i = 0; i < colCount; i++) {LinearLayout colLayout = colLayoutArray.get(i);//回收下方超过两屏bitmapFlowingView bomItem = (FlowingView) colLayout.getChildAt(currentBomLineIndex[i]);if (bomItem.getFootHeight() > t + 3 * viewHeight) {bomItem.recycle();currentBomLineIndex[i] --;}//重载上方进入(-1)两屏以内bitmapFlowingView topItem = (FlowingView) colLayout.getChildAt(Math.max(currentTopLineIndex[i] - 1, 0));if (topItem.getFootHeight() >= t - 2 * viewHeight) {topItem.reload();currentTopLineIndex[i] = Math.max(currentTopLineIndex[i] - 1, 0);}}}super.onScrollChanged(l, t, oldl, oldt);}/** * 这里之所以要用一个Handler，是为了使用他的延迟发送message的函数 * 延迟的效果在于，如果用户快速滑动，手指很早离开屏幕，然后滑动到了底部的时候， * 因为信息稍后发送，在手指离开屏幕到滑动到底部的这个时间差内，依然能够加载图片 * @author carrey * */private static class DelayHandler extends Handler {private WeakReference<WaterFall> waterFallWR;private WaterFall waterFall;public DelayHandler(WaterFall waterFall) {waterFallWR = new WeakReference<WaterFall>(waterFall);this.waterFall = waterFallWR.get();}@Overridepublic void handleMessage(Message msg) {//判断当前滑动到的位置，进行不同的处理if (waterFall.getScrollY() + waterFall.getHeight() >= waterFall.getMaxColHeight() - 20) {//滑动到底部，添加下一页内容waterFall.addNextPageContent(false);} else if (waterFall.getScrollY() == 0) {//滑动到了顶部} else {//滑动在中间位置}super.handleMessage(msg);}}/** * 添加单元到瀑布流中的Handler * @author carrey * */private static class AddItemHandler extends Handler {private WeakReference<WaterFall> waterFallWR;private WaterFall waterFall;public AddItemHandler(WaterFall waterFall) {waterFallWR = new WeakReference<WaterFall>(waterFall);this.waterFall = waterFallWR.get();}@Overridepublic void handleMessage(Message msg) {switch (msg.what) {case 0x00:FlowingView flowingView = (FlowingView)msg.obj;waterFall.addItem(flowingView);break;}super.handleMessage(msg);}}/** * 添加单元到瀑布流中 * @param flowingView */private void addItem(FlowingView flowingView) {int minHeightCol = getMinHeightColIndex();colLayoutArray.get(minHeightCol).addView(flowingView);colHeight[minHeightCol] += flowingView.getViewHeight();flowingView.setFootHeight(colHeight[minHeightCol]);if (!isFirstPage) {bomLineIndex[minHeightCol] ++;currentBomLineIndex[minHeightCol] ++;}}/** * 添加下一个页面的内容 */private void addNextPageContent(boolean isFirstPage) {this.isFirstPage = isFirstPage;//添加下一个页面的pageCount个单元内容for (int i = pageCount * currentPage; i < pageCount * (currentPage + 1) && i < capacity; i++) {new Thread(new PrepareFlowingViewRunnable(i)).run();}currentPage ++;}/** * 异步加载要添加的FlowingView * @author carrey * */private class PrepareFlowingViewRunnable implements Runnable {private int id;public PrepareFlowingViewRunnable (int id) {this.id = id;}@Overridepublic void run() {FlowingView flowingView = new FlowingView(getContext(), id, colWidth);String imageFilePath = "images/" + imageFilePaths[random.nextInt(imageFilePaths.length)];flowingView.setImageFilePath(imageFilePath);flowingView.loadImage();addItemHandler.sendMessage(addItemHandler.obtainMessage(0x00, flowingView));}}/** * 获得所有列中的最大高度 * @return */private int getMaxColHeight() {int maxHeight = colHeight[0];for (int i = 1; i < colHeight.length; i++) {if (colHeight[i] > maxHeight)maxHeight = colHeight[i];}return maxHeight;}/** * 获得目前高度最小的列的索引 * @return */private int getMinHeightColIndex() {int index = 0;for (int i = 1; i < colHeight.length; i++) {if (colHeight[i] < colHeight[index])index = i;}return index;}}

FlowingView.java

package com.carrey.waterfall.waterfall;import java.io.IOException;import java.io.InputStream;import android.content.Context;import android.graphics.Bitmap;import android.graphics.BitmapFactory;import android.graphics.Canvas;import android.graphics.Color;import android.graphics.Paint;import android.graphics.Rect;import android.view.View;import android.widget.Toast;/** * 瀑布流中流动的单元 * @author carrey * */public class FlowingView extends View implements View.OnClickListener, View.OnLongClickListener {/** 单元的编号,在整个瀑布流中是唯一的,可以用来标识身份 */private int index;/** 单元中要显示的图片Bitmap */private Bitmap imageBmp;/** 图像文件的路径 */private String imageFilePath;/** 单元的宽度,也是图像的宽度 */private int width;/** 单元的高度,也是图像的高度 */private int height;/** 画笔 */private Paint paint;/** 图像绘制区域 */private Rect rect;/** 这个单元的底部到它所在列的顶部之间的距离 */private int footHeight;public FlowingView(Context context, int index, int width) {super(context);this.index = index;this.width = width;init();}/** * 基本初始化工作 */private void init() {setOnClickListener(this);setOnLongClickListener(this);paint = new Paint();paint.setAntiAlias(true);}@Overrideprotected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {setMeasuredDimension(width, height);}@Overrideprotected void onDraw(Canvas canvas) {//绘制图像canvas.drawColor(Color.WHITE);if (imageBmp != null && rect != null) {canvas.drawBitmap(imageBmp, null, rect, paint);}super.onDraw(canvas);}/** * 被WaterFall调用异步加载图片数据 */public void loadImage() {InputStream inStream = null;try {inStream = getContext().getAssets().open(imageFilePath);imageBmp = BitmapFactory.decodeStream(inStream);inStream.close();inStream = null;} catch (IOException e) {e.printStackTrace();}if (imageBmp != null) {int bmpWidth = imageBmp.getWidth();int bmpHeight = imageBmp.getHeight();height = (int) (bmpHeight * width / bmpWidth);rect = new Rect(0, 0, width, height);}}/** * 重新加载回收了的Bitmap */public void reload() {if (imageBmp == null) {new Thread(new Runnable() {@Overridepublic void run() {InputStream inStream = null;try {inStream = getContext().getAssets().open(imageFilePath);imageBmp = BitmapFactory.decodeStream(inStream);inStream.close();inStream = null;postInvalidate();} catch (IOException e) {e.printStackTrace();}}}).start();}}/** * 防止OOM进行回收 */public void recycle() {if (imageBmp == null || imageBmp.isRecycled()) return;new Thread(new Runnable() {@Overridepublic void run() {imageBmp.recycle();imageBmp = null;postInvalidate();}}).start();}@Overridepublic boolean onLongClick(View v) {Toast.makeText(getContext(), "long click : " + index, Toast.LENGTH_SHORT).show();return true;}@Overridepublic void onClick(View v) {Toast.makeText(getContext(), "click : " + index, Toast.LENGTH_SHORT).show();}/** * 获取单元的高度 * @return */public int getViewHeight() {return height;}/** * 设置图片路径 * @param imageFilePath */public void setImageFilePath(String imageFilePath) {this.imageFilePath = imageFilePath;}public Bitmap getImageBmp() {return imageBmp;}public void setImageBmp(Bitmap imageBmp) {this.imageBmp = imageBmp;}public int getFootHeight() {return footHeight;}public void setFootHeight(int footHeight) {this.footHeight = footHeight;}}

MainActivity.java

package com.carrey.waterfall;import com.carrey.waterfall.waterfall.WaterFall;import android.os.Bundle;import android.app.Activity;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);WaterFall waterFall = (WaterFall) findViewById(R.id.waterfall);waterFall.setup();}}

activity_main.xml

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:tools="http://schemas.android.com/tools"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context=".MainActivity" >    <com.carrey.waterfall.waterfall.WaterFall         android:id="@+id/waterfall"        android:layout_width="match_parent"        android:layout_height="match_parent"/></RelativeLayout>

源码下载