Android：瀑布流效果 的简单实现

  瀑布流布局结构：

 ScrollView
 *     ------------------------------------------------------------
 *     |      LinearLayout (horizontal)                           |
 *     | -------------------------------------------------------- |
 *     | |      LinearLayout     LinearLayout    LinearLayout   | |
 *     | |  ----------------  ---------------  ---------------  | |
 *     | |  |              |  |             |  |             |  | |
 *     | |  |              |  |             |  |             |  | |
 *     | |  |              |  |             |  |             |  | |
 *     | |  |   Column1    |  |  Column2    |  |  Column3    |  | |
 *     | |  |   Vertical   |  |  Vertical   |  |  Vertical   |  | |
 *     | |  |              |  |             |  |             |  | |
 *     | |  |              |  |             |  |             |  | |
 *     | |  ----------------  ---------------  ---------------  | |
 *     | -------------------------------------------------------- |
 *     ------------------------------------------------------------

布局文件代码如下：

<ScrollView 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"
    android:id="@+id/scrollView"
     >
<LinearLayout
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/pool"
    android:orientation="horizontal"
    >
    
    
</LinearLayout>

</ScrollView>

功能实现代码如下：

package com.don.waterfall_test;

import java.io.IOException;
import java.io.InputStream;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

import android.app.Activity;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.Bundle;
import android.view.Display;
import android.view.MotionEvent;
import android.view.View;
import android.view.View.OnTouchListener;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.LinearLayout.LayoutParams;
import android.widget.ScrollView;

public class MainActivity extends Activity implements OnTouchListener {
   private ScrollView scrollView;
   private LinearLayout pool;
   private List<LinearLayout> items_layout; //用于存放动态生成的线性布局
   private AssetManager manager; //assets文件夹的管理器
   private int screenWidth;  //屏幕的宽度
   private List<String> namesList; //用于存放所有图片文件的文件名    
   private int currentIndex = 0;; //表示当前页从第几
    
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        
        scrollView = (ScrollView) findViewById(R.id.scrollView);
        scrollView.setOnTouchListener(this);
        pool = (LinearLayout) findViewById(R.id.pool);
        
        manager = getAssets();
        
        Display display = getWindowManager().getDefaultDisplay();
        screenWidth = display.getWidth();
        
        createLayouts();
        
        getPicNameList();
         loadImage(currentIndex);
   
    }
    
    /**
     *  动态生成三个垂直的线性布局
     */
    public void createLayouts(){
        items_layout = new ArrayList<LinearLayout>();
        for(int i = 0; i < 3; i++){
            LinearLayout item_layout = new LinearLayout(this);
            item_layout.setOrientation(LinearLayout.VERTICAL);
            LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(screenWidth/3,android.view.ViewGroup.LayoutParams.WRAP_CONTENT);
            item_layout.setLayoutParams(params);
            //将该线性布局添加到pool中
            pool.addView(item_layout);
            //将该线性布局添加到集合中
            items_layout.add(item_layout);
        }
        
    }
    
    /**
     *   //将assets文件夹下的图片名存到集合中
     */
    public void getPicNameList(){
        
        namesList = new ArrayList<String>();
        try {
            //获取到images文件夹下所有图片的文件名数组
            String[] names = manager.list("images");
            //将字符串数据转换为集合
            namesList.addAll(Arrays.asList(names));
        } catch (IOException e) {
            e.printStackTrace();
        }
        
    }
    /**
     *  从指定索引位置处加载图片
     * @param currentIndex
     */
    public void loadImage(int index ){
        
        //用于一次加载的图片的文件名，一次加载9张
        String[] paths = new String[9];
        for(int i = index ,j = 0; i < index +9;i++,j++){
            if(i >= namesList.size()){
                break;
            }
            paths[j] = namesList.get(i);
            
        }
        
       //获取到图片路径后，就开始加载图片
        int count = 0; //用于计算加载的paths中的第几张图片
        for(String fileName : paths){
            try {
                //获得bitmap对象
                InputStream is = manager.open("images/"+fileName);
                Bitmap bitmap = BitmapFactory.decodeStream(is);
                
                //动态创建ImageView
                ImageView image = new ImageView(this);
                //设置image的初始尺寸
                LinearLayout.LayoutParams params1 = new LinearLayout.LayoutParams(screenWidth/3,LinearLayout.LayoutParams.WRAP_CONTENT);
                image.setLayoutParams(params1);
                //为image设置默认图片
                image.setImageResource(R.drawable.ic_launcher);
                
                //根据bitmap的大小，重新设置image的高度
                LayoutParams params2 =   (LayoutParams) image.getLayoutParams();
                params2.height = params2.width * bitmap.getHeight()/bitmap.getWidth();
                image.setLayoutParams(params2);
                image.setImageBitmap(bitmap);
                
                //将image添加到垂直线性布局中
                  items_layout.get(count%3).addView(image);
                  count++;
                
            } catch (IOException e) {
                e.printStackTrace();
            }
        }
    }
    
    /**
     *  为scrollView添加触摸事件
     */
    @Override
    public boolean onTouch(View view , MotionEvent event) {
    
        int action = event.getAction();
        if(action == MotionEvent.ACTION_UP){ //手指离开屏幕时加载图片
            
            int sy = scrollView.getScrollY(); //滑出scrollView上边界的部分的高度
            int sh = scrollView.getHeight();  //scrollView的高度
            
            int ph = pool.getHeight(); //得到pool的高度
             
            if(sy + sh >= ph){
                currentIndex += 9;
                
                /** 
                 *   方式一：
                 *   
                 * 重复加载所有的图片，过多时，会发生OOM异常
                 * *//*
                if(currentIndex >= namesList.size()){
                    currentIndex = 0;
                }
                loadImage(currentIndex);*/
                
                
                /**
                 *  方式二： 
                 *   将所有的图片只加载一次
                 */
                if(currentIndex < namesList.size()){
                    loadImage(currentIndex);
                }
            }
            
        }
        return false;
    }

}