Android 基础之图片加载（三）
2019-02-18 本文已影响0人
Kevin_小飞象
LruCache和DiskLruCache完美结合。
效果图
photo.jpg
1. 配置一下 AndroidManifest.xml 文件，并加入相应的权限
<uses-permission android:name="android.permission.INTERNET" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
2. 新建一个 libcore.io 包，并将 DiskLruCache.java 文件拷贝到这个包下
io.jpg
3. 图片资源，新建一个 Images 类
/**
* Created on 2019/2/18 14:55
*
* @author Scarf Gong
*/
public class Images {
public final static String[] imageThumbUrls = new String[] {
"https://img-my.csdn.net/uploads/201407/26/1406383299_1976.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383291_6518.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383291_8239.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383290_9329.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383290_1042.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383275_3977.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383265_8550.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383264_3954.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383264_4787.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383264_8243.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383248_3693.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383243_5120.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383242_3127.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383242_9576.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383242_1721.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383219_5806.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383214_7794.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383213_4418.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383213_3557.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383210_8779.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383172_4577.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383166_3407.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383166_2224.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383166_7301.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383165_7197.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383150_8410.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383131_3736.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383130_5094.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383130_7393.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383129_8813.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383100_3554.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383093_7894.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383092_2432.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383092_3071.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383091_3119.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383059_6589.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383059_8814.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383059_2237.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383058_4330.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406383038_3602.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382942_3079.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382942_8125.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382942_4881.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382941_4559.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382941_3845.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382924_8955.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382923_2141.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382923_8437.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382922_6166.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382922_4843.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382905_5804.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382904_3362.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382904_2312.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382904_4960.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382900_2418.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382881_4490.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382881_5935.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382880_3865.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382880_4662.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382879_2553.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382862_5375.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382862_1748.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382861_7618.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382861_8606.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382861_8949.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382841_9821.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382840_6603.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382840_2405.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382840_6354.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382839_5779.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382810_7578.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382810_2436.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382809_3883.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382809_6269.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382808_4179.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382790_8326.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382789_7174.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382789_5170.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382789_4118.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382788_9532.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382767_3184.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382767_4772.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382766_4924.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382766_5762.jpg",
"https://img-my.csdn.net/uploads/201407/26/1406382765_7341.jpg"
};
}
4. 修改activity_main.xml中的代码,添加GridView
<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout 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">
<GridView
android:id="@+id/photo_wall"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:columnWidth="@dimen/image_thumbnail_size"
android:gravity="center"
android:horizontalSpacing="@dimen/image_thumbnail_spacing"
android:numColumns="auto_fit"
android:stretchMode="columnWidth"
android:verticalSpacing="@dimen/image_thumbnail_spacing"/>
</android.support.constraint.ConstraintLayout>
5. 定义 GridView 中每一个子View的布局，新建一个 item_grid_photo.xml 布局
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="wrap_content"
android:layout_height="wrap_content">
<ImageView
android:id="@+id/photo"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:layout_centerInParent="true"
android:scaleType="fitXY"/>
</RelativeLayout>
6. 新建 PhotoWallAdapter 做为 GridView 的适配器，代码如下所示：
import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.os.AsyncTask;
import android.os.Environment;
import android.support.annotation.NonNull;
import android.support.annotation.Nullable;
import android.util.LruCache;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.GridView;
import android.widget.ImageView;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileDescriptor;
import java.io.FileInputStream;
import java.io.IOException;
import java.io.OutputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.util.HashSet;
import java.util.Set;
import libcore.io.DiskLruCache;
/**
* Created on 2019/2/18 15:03
*
* GridView的适配器，负责异步从网络上下载图片展示在照片墙上。
*
* @author Scarf Gong
*/
public class PhotoWallAdapter extends ArrayAdapter<String> {
// 记录所有正在下载或等待下载的任务。
private Set<BitmapWorkerTask> taskCollection;
//图片缓存技术的核心类，用于缓存所有下载好的图片，在程序内存达到设定值时会将最少最近使用的图片移除掉。
private LruCache<String, Bitmap> mMemoryCache;
//图片硬盘缓存核心类。
private DiskLruCache mDiskLruCache;
//GridView的实例
private GridView mPhotoWall;
//记录每个子项的高度。
private int mItemHeight = 0;
public PhotoWallAdapter(Context context, int textViewResourceId, String[] objects, GridView photoWall) {
super(context, textViewResourceId, objects);
mPhotoWall = photoWall;
taskCollection = new HashSet<BitmapWorkerTask>();
// 获取应用程序最大可用内存
int maxMemory = (int) Runtime.getRuntime().maxMemory();
int cacheSize = maxMemory / 8;
// 设置图片缓存大小为程序最大可用内存的1/8
mMemoryCache = new LruCache<String, Bitmap>(cacheSize) {
@Override
protected int sizeOf(String key, Bitmap bitmap) {
return bitmap.getByteCount();
}
};
try {
// 获取图片缓存路径
File cacheDir = getDiskCacheDir(context, "thumb");
if (!cacheDir.exists()) {
cacheDir.mkdirs();
}
// 创建DiskLruCache实例，初始化缓存数据
mDiskLruCache = DiskLruCache
.open(cacheDir, getAppVersion(context), 1, 10 * 1024 * 1024);
} catch (IOException e) {
e.printStackTrace();
}
}
@NonNull
@Override
public View getView(int position, @Nullable View convertView, @NonNull ViewGroup parent) {
final String url = getItem(position);
View view;
if (convertView == null) {
view = LayoutInflater.from(getContext()).inflate(R.layout.item_grid_photo, null);
} else {
view = convertView;
}
final ImageView imageView = (ImageView) view.findViewById(R.id.photo);
if (imageView.getLayoutParams().height != mItemHeight) {
imageView.getLayoutParams().height = mItemHeight;
}
// 给ImageView设置一个Tag，保证异步加载图片时不会乱序
imageView.setTag(url);
imageView.setImageResource(R.drawable.empty_photo);
loadBitmaps(imageView, url);
return view;
}
/**
* 将一张图片存储到LruCache中。
*/
public void addBitmapToMemoryCache(String key, Bitmap bitmap) {
if (getBitmapFromMemoryCache(key) == null) {
mMemoryCache.put(key, bitmap);
}
}
/**
* 从LruCache中获取一张图片，如果不存在就返回null。
*
* @param key
* LruCache的键，这里传入图片的URL地址。
* @return 对应传入键的Bitmap对象，或者null。
*/
public Bitmap getBitmapFromMemoryCache(String key) {
return mMemoryCache.get(key);
}
/**
* 加载Bitmap对象。此方法会在LruCache中检查所有屏幕中可见的ImageView的Bitmap对象，
* 如果发现任何一个ImageView的Bitmap对象不在缓存中，就会开启异步线程去下载图片。
*/
public void loadBitmaps(ImageView imageView, String imageUrl) {
try {
Bitmap bitmap = getBitmapFromMemoryCache(imageUrl);
if (bitmap == null) {
BitmapWorkerTask task = new BitmapWorkerTask();
taskCollection.add(task);
task.execute(imageUrl);
} else {
if (imageView != null && bitmap != null) {
imageView.setImageBitmap(bitmap);
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
/**
* 取消所有正在下载或等待下载的任务。
*/
public void cancelAllTasks() {
if (taskCollection != null) {
for (BitmapWorkerTask task : taskCollection) {
task.cancel(false);
}
}
}
/**
* 根据传入的uniqueName获取硬盘缓存的路径地址。
*/
public File getDiskCacheDir(Context context, String uniqueName) {
String cachePath;
if (Environment.MEDIA_MOUNTED.equals(Environment.getExternalStorageState())
|| !Environment.isExternalStorageRemovable()) {
cachePath = context.getExternalCacheDir().getPath();
} else {
cachePath = context.getCacheDir().getPath();
}
return new File(cachePath + File.separator + uniqueName);
}
/**
* 获取当前应用程序的版本号。
*/
public int getAppVersion(Context context) {
try {
PackageInfo info = context.getPackageManager().getPackageInfo(context.getPackageName(),
0);
return info.versionCode;
} catch (PackageManager.NameNotFoundException e) {
e.printStackTrace();
}
return 1;
}
/**
* 设置item子项的高度。
*/
public void setItemHeight(int height) {
if (height == mItemHeight) {
return;
}
mItemHeight = height;
notifyDataSetChanged();
}
/**
* 使用MD5算法对传入的key进行加密并返回。
*/
public String hashKeyForDisk(String key) {
String cacheKey;
try {
final MessageDigest mDigest = MessageDigest.getInstance("MD5");
mDigest.update(key.getBytes());
cacheKey = bytesToHexString(mDigest.digest());
} catch (NoSuchAlgorithmException e) {
cacheKey = String.valueOf(key.hashCode());
}
return cacheKey;
}
/**
* 将缓存记录同步到journal文件中。
*/
public void fluchCache() {
if (mDiskLruCache != null) {
try {
mDiskLruCache.flush();
} catch (IOException e) {
e.printStackTrace();
}
}
}
private String bytesToHexString(byte[] bytes) {
StringBuilder sb = new StringBuilder();
for (int i = 0; i < bytes.length; i++) {
String hex = Integer.toHexString(0xFF & bytes[i]);
if (hex.length() == 1) {
sb.append('0');
}
sb.append(hex);
}
return sb.toString();
}
/**
* Created on 2019/2/18 15:15
* 异步下载图片的任务。
* @author Scarf Gong
*/
public class BitmapWorkerTask extends AsyncTask<String, Void, Bitmap> {
/**
* 图片的URL地址
*/
private String imageUrl;
@Override
protected Bitmap doInBackground(String... params) {
imageUrl = params[0];
FileDescriptor fileDescriptor = null;
FileInputStream fileInputStream = null;
DiskLruCache.Snapshot snapShot = null;
try {
// 生成图片URL对应的key
final String key = hashKeyForDisk(imageUrl);
// 查找key对应的缓存
snapShot = mDiskLruCache.get(key);
if (snapShot == null) {
// 如果没有找到对应的缓存，则准备从网络上请求数据，并写入缓存
DiskLruCache.Editor editor = mDiskLruCache.edit(key);
if (editor != null) {
OutputStream outputStream = editor.newOutputStream(0);
if (downloadUrlToStream(imageUrl, outputStream)) {
editor.commit();
} else {
editor.abort();
}
}
// 缓存被写入后，再次查找key对应的缓存
snapShot = mDiskLruCache.get(key);
}
if (snapShot != null) {
fileInputStream = (FileInputStream) snapShot.getInputStream(0);
fileDescriptor = fileInputStream.getFD();
}
// 将缓存数据解析成Bitmap对象
Bitmap bitmap = null;
if (fileDescriptor != null) {
bitmap = BitmapFactory.decodeFileDescriptor(fileDescriptor);
}
if (bitmap != null) {
// 将Bitmap对象添加到内存缓存当中
addBitmapToMemoryCache(params[0], bitmap);
}
return bitmap;
} catch (IOException e) {
e.printStackTrace();
} finally {
if (fileDescriptor == null && fileInputStream != null) {
try {
fileInputStream.close();
} catch (IOException e) {
}
}
}
return null;
}
@Override
protected void onPostExecute(Bitmap bitmap) {
super.onPostExecute(bitmap);
// 根据Tag找到相应的ImageView控件，将下载好的图片显示出来。
ImageView imageView = (ImageView) mPhotoWall.findViewWithTag(imageUrl);
if (imageView != null && bitmap != null) {
imageView.setImageBitmap(bitmap);
}
taskCollection.remove(this);
}
/**
* 建立HTTP请求，并获取Bitmap对象。
*/
private boolean downloadUrlToStream(String urlString, OutputStream outputStream) {
HttpURLConnection urlConnection = null;
BufferedOutputStream out = null;
BufferedInputStream in = null;
try {
final URL url = new URL(urlString);
urlConnection = (HttpURLConnection) url.openConnection();
in = new BufferedInputStream(urlConnection.getInputStream(), 8 * 1024);
out = new BufferedOutputStream(outputStream, 8 * 1024);
int b;
while ((b = in.read()) != -1) {
out.write(b);
}
return true;
} catch (final IOException e) {
e.printStackTrace();
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
try {
if (out != null) {
out.close();
}
if (in != null) {
in.close();
}
} catch (final IOException e) {
e.printStackTrace();
}
}
return false;
}
}
}
7. 编写MainActivity的代码
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.ViewTreeObserver;
import android.widget.GridView;
public class MainActivity extends AppCompatActivity {
/**
* 用于展示照片墙的GridView
*/
private GridView mPhotoWall;
/**
* GridView的适配器
*/
private PhotoWallAdapter mAdapter;
private int mImageThumbSize;
private int mImageThumbSpacing;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mImageThumbSize = getResources().getDimensionPixelSize(
R.dimen.image_thumbnail_size);
mImageThumbSpacing = getResources().getDimensionPixelSize(
R.dimen.image_thumbnail_spacing);
mPhotoWall = (GridView) findViewById(R.id.photo_wall);
mAdapter = new PhotoWallAdapter(this, 0, Images.imageThumbUrls,
mPhotoWall);
mPhotoWall.setAdapter(mAdapter);
mPhotoWall.getViewTreeObserver().addOnGlobalLayoutListener(
new ViewTreeObserver.OnGlobalLayoutListener() {
@Override
public void onGlobalLayout() {
final int numColumns = (int) Math.floor(mPhotoWall
.getWidth()
/ (mImageThumbSize + mImageThumbSpacing));
if (numColumns > 0) {
int columnWidth = (mPhotoWall.getWidth() / numColumns)
- mImageThumbSpacing;
mAdapter.setItemHeight(columnWidth);
mPhotoWall.getViewTreeObserver()
.removeGlobalOnLayoutListener(this);
}
}
});
}
@Override
protected void onPause() {
super.onPause();
mAdapter.fluchCache();
}
@Override
protected void onDestroy() {
super.onDestroy();
mAdapter.cancelAllTasks();
}
}
好了，全部代码都在这儿了，让我们来运行一下吧!!!
