更新图片缓存

app/src/main/java/com/example/myapplication/ImageLoader.java

@@ -2,45 +2,104 @@ package com.example.myapplication;
 
 import android.graphics.Bitmap;
 import android.graphics.BitmapFactory;
+import android.os.AsyncTask;
 import android.os.Handler;
 import android.os.Message;
+import android.util.LruCache;
 import android.widget.ImageView;
+import android.widget.ListView;
 
 import javax.net.ssl.HttpsURLConnection;
 import java.io.BufferedInputStream;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.URL;
+import java.util.HashSet;
+import java.util.Set;
 
 public class ImageLoader {
 
     private ImageView mImageView;
     private String murl;
-    private Handler handler = new Handler(){
-        @Override
-        public void handleMessage(Message msg) {
-            super.handleMessage(msg);
-            if(mImageView.getTag().equals(murl)) {
-                mImageView.setImageBitmap((Bitmap) msg.obj);
-            }
-        }
-    };
+    //创建Cache
+    private LruCache<String, Bitmap> mCaches;
+    private ListView mListView;
+    private Set<NewsAsyncTask> mTask;
 
-    public void showImagerByThread(ImageView imageView, final String url){
-        mImageView = imageView;
-        murl = url;
-        new Thread(){
+    public ImageLoader(ListView listView){
+        //构造方法
+        mListView = listView;
+        mTask = new HashSet<>();
+        //获取最大可用内存
+        int  maxMemory = (int) Runtime.getRuntime().maxMemory();
+        //缓存为内存的四分之一
+        int cacheSize = maxMemory / 4;
+        mCaches = new LruCache<String, Bitmap>(cacheSize){
             @Override
-            public void run() {
-                super.run();
-                Bitmap bitmap = getBitmapFromURL(url);
-                Message message = Message.obtain();
-                message.obj = bitmap;
-                handler.sendMessage(message);
+            protected int sizeOf(String key, Bitmap value) {
+                //每次加入内存缓存的时候进行调用,把value的实际大小放进去
+                return value.getByteCount();
             }
-        }.start();
+        };
+
+    }
+
+    /**
+     * 增加到缓存
+     * @param url
+     * @param bitmap
+     */
+    public void addBitmapToCache(String url, Bitmap bitmap){
+        //判断缓存中是否有这个值
+        if(getBitmapFromCache(url) == null){
+            mCaches.put(url, bitmap);
+        }
+    }
+
+    /**
+     * 从缓存中读取数据
+     * @param url
+     * @return
+     */
+    public Bitmap getBitmapFromCache(String url){
+        //获取缓存的对象
+        return mCaches.get(url);
     }
 
+//    private Handler handler = new Handler(){
+//        @Override
+//        public void handleMessage(Message msg) {
+//            super.handleMessage(msg);
+//            //接受message
+//            if(mImageView.getTag().equals(murl)) {
+//                //url相同的时候才设置view，防止图片一样
+//                mImageView.setImageBitmap((Bitmap) msg.obj);
+//            }
+//        }
+//    };
+//
+//    public void showImagerByThread(ImageView imageView, final String url){
+//        //把两个值保存给上面的子线程使用
+//        mImageView = imageView;
+//        murl = url;
+//        new Thread(){
+//            @Override
+//            public void run() {
+//                super.run();
+//                Bitmap bitmap = getBitmapFromURL(url);
+//                Message message = Message.obtain();
+//                message.obj = bitmap;
+//                //发送message
+//                handler.sendMessage(message);
+//            }
+//        }.start();
+//    }
+
+    /**
+     * 根据url获取图片的Bitmap对象
+     * @param urlString
+     * @return
+     */
     public Bitmap getBitmapFromURL(String urlString){
         Bitmap bitmap;
         InputStream is = null;
@@ -62,4 +121,90 @@ public class ImageLoader {
         }
         return null;
     }
+
+    public void showImageByAsyncTask(ImageView imageView,String url){
+        //判断缓存中是否有
+        Bitmap bitmap = getBitmapFromCache(url);
+        if(bitmap == null){
+            //缓存中没有就去下载
+            //new NewsAsyncTask(imageView, url).execute(url);
+
+            //没有就给默认的
+            imageView.setImageResource(R.mipmap.ic_launcher);
+        }else{
+            imageView.setImageBitmap(bitmap);
+        }
+
+    }
+
+    /**
+     * 停止运行的任务
+     */
+    public void cancelAllTasks(){
+        if(mTask != null){
+            for (NewsAsyncTask task : mTask){
+                task.cancel(false);
+            }
+        }
+    }
+    
+    public void loadImages(int start, int end){
+        for (int i = start; i < end; i++) {
+            String url = NewsAdapter.URLS[i];
+            //判断缓存中是否有
+            Bitmap bitmap = getBitmapFromCache(url);
+            if(bitmap == null){
+                //缓存中没有就去下载
+                //new NewsAsyncTask(imageView, url).execute(url);
+                NewsAsyncTask task = new NewsAsyncTask(url);
+                task.execute(url);
+                mTask.add(task);
+            }else{
+                //imageView.setImageBitmap(bitmap);
+                ImageView imageView = mListView.findViewWithTag(url);
+                imageView.setImageBitmap(bitmap);
+            }
+        }
+    }
+
+    /**
+     * AsyncTask的方式把图片放入view
+     */
+    private class NewsAsyncTask extends AsyncTask<String, Void, Bitmap>{
+
+        //private ImageView mImageView;
+        private String murl;
+
+        public NewsAsyncTask(String url){
+            //mImageView = imageView;
+            murl = url;
+        }
+
+        @Override
+        protected Bitmap doInBackground(String... strings) {
+            String url = strings[0];
+            //从网络中获取图片
+            Bitmap bitmap = getBitmapFromURL(url);
+            if(bitmap != null){
+                //增加到缓存
+                addBitmapToCache(url, bitmap);
+            }
+            return bitmap;
+        }
+
+        @Override
+        protected void onPostExecute(Bitmap bitmap) {
+            super.onPostExecute(bitmap);
+            //防止图片重复判断唯一性
+//            if(mImageView.getTag().equals(murl)) {
+//                mImageView.setImageBitmap(bitmap);
+//            }
+            ImageView imageView = mListView.findViewWithTag(murl);
+            imageView.setImageBitmap(bitmap);
+            if(imageView != null && bitmap != null){
+                imageView.setImageBitmap(bitmap);
+            }
+            mTask.remove(this);
+        }
+    }
 }

app/src/main/java/com/example/myapplication/MainActivity.java

@@ -30,6 +30,7 @@ public class MainActivity extends AppCompatActivity {
         setContentView(R.layout.activity_main);
         mListView = (ListView) findViewById(R.id.new_main);
 
+        //点击事件
         mListView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
             @Override
             public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
@@ -60,7 +61,7 @@ public class MainActivity extends AppCompatActivity {
         @Override
         protected void onPostExecute(List<NewBean> newBeans) {
             super.onPostExecute(newBeans);
-            NewsAdapter adapter = new NewsAdapter(MainActivity.this, newBeans);
+            NewsAdapter adapter = new NewsAdapter(MainActivity.this, newBeans, mListView);
             mListView.setAdapter(adapter);
         }
     }

app/src/main/java/com/example/myapplication/NewBean.java

@@ -1,7 +1,5 @@
 package com.example.myapplication;
 
-import java.util.Date;
-
 public class NewBean {
 
     private String id;

app/src/main/java/com/example/myapplication/NewsAdapter.java

@@ -4,20 +4,33 @@ import android.content.Context;
 import android.view.LayoutInflater;
 import android.view.View;
 import android.view.ViewGroup;
-import android.widget.BaseAdapter;
-import android.widget.ImageView;
-import android.widget.TextView;
+import android.widget.*;
 
 import java.util.List;
 
-public class NewsAdapter extends BaseAdapter {
+public class NewsAdapter extends BaseAdapter implements AbsListView.OnScrollListener {
 
     private List<NewBean> mList;
     private LayoutInflater mInflater;
+    private ImageLoader mImageLoader;
+    private int mstart,mend;
+    public static String[] URLS;
+    //是否第一次启动
+    private boolean mFirst;
 
-    public NewsAdapter(Context context, List<NewBean> data){
+    public NewsAdapter(Context context, List<NewBean> data, ListView listView){
+        //构造方法
         mList = data;
         mInflater = LayoutInflater.from(context);
+        mImageLoader = new ImageLoader(listView);
+        URLS = new String[data.size()];
+        for (int i = 0;i < data.size();i++){
+            URLS[i] = data.get(i).getPicUrl();
+        }
+        //绑定监听事件
+        listView.setOnScrollListener(this);
+        //初始化值
+        mFirst = true;
     }
 
     @Override
@@ -53,7 +66,9 @@ public class NewsAdapter extends BaseAdapter {
         viewHolder.newPic.setImageResource(R.mipmap.ic_launcher);
         String url = mList.get(position).getPicUrl();
         viewHolder.newPic.setTag(url);
-        new ImageLoader().showImagerByThread(viewHolder.newPic, mList.get(position).getPicUrl());
+        //new ImageLoader().showImagerByThread(viewHolder.newPic, mList.get(position).getPicUrl());
+        //new ImageLoader().showImageByAsyncTask(viewHolder.newPic, mList.get(position).getPicUrl());
+        mImageLoader.showImageByAsyncTask(viewHolder.newPic, mList.get(position).getPicUrl());
         viewHolder.newTitle.setText(mList.get(position).getTitle());
         viewHolder.newTime.setText(mList.get(position).getTime());
         viewHolder.newDesc.setText(mList.get(position).getDesc());
@@ -61,6 +76,30 @@ public class NewsAdapter extends BaseAdapter {
         return convertView;
     }
 
+    @Override
+    public void onScrollStateChanged(AbsListView view, int scrollState) {
+        //滑动状态的时候调用
+        if(scrollState == SCROLL_STATE_IDLE){
+            //停止滚动的时候
+            mImageLoader.loadImages(mstart,mend);
+        } else{
+            //停止任务
+            mImageLoader.cancelAllTasks();
+        }
+    }
+
+    @Override
+    public void onScroll(AbsListView view, int firstVisibleItem, int visibleItemCount, int totalItemCount) {
+        //滑不滑动都会调用
+        mstart = firstVisibleItem;
+        mend = firstVisibleItem + visibleItemCount;
+        //第一次显示调用
+        if(mFirst == true && visibleItemCount > 0){
+            mImageLoader.loadImages(mstart,mend);
+            mFirst = false;
+        }
+    }
+
     class ViewHolder{
         public TextView newTitle, newTime, newDesc, newContent;
         public ImageView newPic;