Android：瀑布流效果 的简单实现

  1 package com.don.waterfall_test;
  2 
  3 import java.io.IOException;
  4 import java.io.InputStream;
  5 import java.util.ArrayList;
  6 import java.util.Arrays;
  7 import java.util.List;
  8 
  9 import android.app.Activity;
 10 import android.content.res.AssetManager;
 11 import android.graphics.Bitmap;
 12 import android.graphics.BitmapFactory;
 13 import android.os.Bundle;
 14 import android.view.Display;
 15 import android.view.MotionEvent;
 16 import android.view.View;
 17 import android.view.View.OnTouchListener;
 18 import android.widget.ImageView;
 19 import android.widget.LinearLayout;
 20 import android.widget.LinearLayout.LayoutParams;
 21 import android.widget.ScrollView;
 22 
 23 public class MainActivity extends Activity implements OnTouchListener {
 24    private ScrollView scrollView;
 25    private LinearLayout pool;
 26    private List<LinearLayout> items_layout; //用于存放动态生成的线性布局
 27    private AssetManager manager; //assets文件夹的管理器
 28    private int screenWidth;  //屏幕的宽度
 29    private List<String> namesList; //用于存放所有图片文件的文件名    
 30    private int currentIndex = 0;; //表示当前页从第几
 31     
 32     @Override
 33     protected void onCreate(Bundle savedInstanceState) {
 34         super.onCreate(savedInstanceState);
 35         setContentView(R.layout.activity_main);
 36         
 37         scrollView = (ScrollView) findViewById(R.id.scrollView);
 38         scrollView.setOnTouchListener(this);
 39         pool = (LinearLayout) findViewById(R.id.pool);
 40         
 41         manager = getAssets();
 42         
 43         Display display = getWindowManager().getDefaultDisplay();
 44         screenWidth = display.getWidth();
 45         
 46         createLayouts();
 47         
 48         getPicNameList();
 49          loadImage(currentIndex);
 50    
 51     }
 52     
 53     /**
 54      *  动态生成三个垂直的线性布局
 55      */
 56     public void createLayouts(){
 57         items_layout = new ArrayList<LinearLayout>();
 58         for(int i = 0; i < 3; i++){
 59             LinearLayout item_layout = new LinearLayout(this);
 60             item_layout.setOrientation(LinearLayout.VERTICAL);
 61             LinearLayout.LayoutParams params = new LinearLayout.LayoutParams(screenWidth/3,android.view.ViewGroup.LayoutParams.WRAP_CONTENT);
 62             item_layout.setLayoutParams(params);
 63             //将该线性布局添加到pool中
 64             pool.addView(item_layout);
 65             //将该线性布局添加到集合中
 66             items_layout.add(item_layout);
 67         }
 68         
 69     }
 70     
 71     /**
 72      *   //将assets文件夹下的图片名存到集合中
 73      */
 74     public void getPicNameList(){
 75         
 76         namesList = new ArrayList<String>();
 77         try {
 78             //获取到images文件夹下所有图片的文件名数组
 79             String[] names = manager.list("images");
 80             //将字符串数据转换为集合
 81             namesList.addAll(Arrays.asList(names));
 82         } catch (IOException e) {
 83             e.printStackTrace();
 84         }
 85         
 86     }
 87     /**
 88      *  从指定索引位置处加载图片
 89      * @param currentIndex
 90      */
 91     public void loadImage(int index ){
 92         
 93         //用于一次加载的图片的文件名，一次加载9张
 94         String[] paths = new String[9];
 95         for(int i = index ,j = 0; i < index +9;i++,j++){
 96             if(i >= namesList.size()){
 97                 break;
 98             }
 99             paths[j] = namesList.get(i);
100             
101         }
102         
103        //获取到图片路径后，就开始加载图片
104         int count = 0; //用于计算加载的paths中的第几张图片
105         for(String fileName : paths){
106             try {
107                 //获得bitmap对象
108                 InputStream is = manager.open("images/"+fileName);
109                 Bitmap bitmap = BitmapFactory.decodeStream(is);
110                 
111                 //动态创建ImageView
112                 ImageView image = new ImageView(this);
113                 //设置image的初始尺寸
114                 LinearLayout.LayoutParams params1 = new LinearLayout.LayoutParams(screenWidth/3,LinearLayout.LayoutParams.WRAP_CONTENT);
115                 image.setLayoutParams(params1);
116                 //为image设置默认图片
117                 image.setImageResource(R.drawable.ic_launcher);
118                 
119                 //根据bitmap的大小，重新设置image的高度
120                 LayoutParams params2 =   (LayoutParams) image.getLayoutParams();
121                 params2.height = params2.width * bitmap.getHeight()/bitmap.getWidth();
122                 image.setLayoutParams(params2);
123                 image.setImageBitmap(bitmap);
124                 
125                 //将image添加到垂直线性布局中
126                   items_layout.get(count%3).addView(image);
127                   count++;
128                 
129             } catch (IOException e) {
130                 e.printStackTrace();
131             }
132         }
133     }
134     
135     /**
136      *  为scrollView添加触摸事件
137      */
138     @Override
139     public boolean onTouch(View view , MotionEvent event) {
140     
141         int action = event.getAction();
142         if(action == MotionEvent.ACTION_UP){ //手指离开屏幕时加载图片
143             
144             int sy = scrollView.getScrollY(); //滑出scrollView上边界的部分的高度
145             int sh = scrollView.getHeight();  //scrollView的高度
146             
147             int ph = pool.getHeight(); //得到pool的高度
148              
149             if(sy + sh >= ph){
150                 currentIndex += 9;
151                 
152                 /** 
153                  *   方式一：
154                  *   
155                  * 重复加载所有的图片，过多时，会发生OOM异常
156                  * *//*
157                 if(currentIndex >= namesList.size()){
158                     currentIndex = 0;
159                 }
160                 loadImage(currentIndex);*/
161                 
162                 
163                 /**
164                  *  方式二： 
165                  *   将所有的图片只加载一次
166                  */
167                 if(currentIndex < namesList.size()){
168                     loadImage(currentIndex);
169                 }
170             }
171             
172         }
173         return false;
174     }
175 
176 }