异步加载图片的目的只有一个:让用户体验更好
因为异步加载不利用主线程(UI线程)
一、源码结构:
二、异步图片加载器(实现异步加载的核心)
- package com.ning.lazytest;
- import java.io.IOException;
- import java.io.InputStream;
- import java.lang.ref.SoftReference;
- import java.net.MalformedURLException;
- import java.net.URL;
- import java.util.HashMap;
- import android.graphics.drawable.Drawable;
- import android.os.Handler;
- import android.os.Message;
- public class AsyncImageLoader {
- private HashMap<String, SoftReference<Drawable>> imageCache;
- public AsyncImageLoader() {
- imageCache = new HashMap<String, SoftReference<Drawable>>();
- }
- public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {
- if (imageCache.containsKey(imageUrl)) {
- SoftReference<Drawable> softReference = imageCache.get(imageUrl);
- Drawable drawable = softReference.get();
- if (drawable != null) {
- return drawable;
- }
- }
- final Handler handler = new Handler() {
- public void handleMessage(Message message) {
- imageCallback.imageLoaded((Drawable) message.obj, imageUrl);
- }
- };
- new Thread() {
- @Override
- public void run() {
- Drawable drawable = loadImageFromUrl(imageUrl);
- imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
- Message message = handler.obtainMessage(0, drawable);
- handler.sendMessage(message);
- }
- }.start();
- return null;
- }
- public static Drawable loadImageFromUrl(String url) {
- URL m;
- InputStream i = null;
- try {
- m = new URL(url);
- i = (InputStream) m.getContent();
- } catch (MalformedURLException e1) {
- e1.printStackTrace();
- } catch (IOException e) {
- e.printStackTrace();
- }
- Drawable d = Drawable.createFromStream(i, "src");
- return d;
- }
- public interface ImageCallback {
- public void imageLoaded(Drawable imageDrawable, String imageUrl);
- }
- }
三、ListView适配器
- package com.ning.lazytest;
- import java.util.List;
- import com.ning.lazytest.AsyncImageLoader.ImageCallback;
- import android.app.Activity;
- import android.graphics.drawable.Drawable;
- import android.view.LayoutInflater;
- import android.view.View;
- import android.view.ViewGroup;
- import android.widget.ArrayAdapter;
- import android.widget.ImageView;
- import android.widget.ListView;
- import android.widget.TextView;
- public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText>{
- private ListView listView;
- private AsyncImageLoader asyncImageLoader;
- public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts, ListView listView) {
- super(activity, 0, imageAndTexts);
- this.listView = listView;
- asyncImageLoader = new AsyncImageLoader();
- }
- public View getView(int position, View convertView, ViewGroup parent) {
- Activity activity = (Activity) getContext();
- // Inflate the views from XML
- View rowView = convertView;
- ViewCache viewCache;
- if (rowView == null) {
- LayoutInflater inflater = activity.getLayoutInflater();
- rowView = inflater.inflate(R.layout.image_and_text_row, null);
- viewCache = new ViewCache(rowView);
- rowView.setTag(viewCache);
- } else {
- viewCache = (ViewCache) rowView.getTag();
- }
- ImageAndText imageAndText = getItem(position);
- // Load the image and set it on the ImageView
- String imageUrl = imageAndText.getImageUrl();
- ImageView imageView = viewCache.getImageView();
- imageView.setTag(imageUrl);
- Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, new ImageCallback() {
- public void imageLoaded(Drawable imageDrawable, String imageUrl) {
- ImageView imageViewByTag = (ImageView) listView.findViewWithTag(imageUrl);
- if (imageViewByTag != null) {
- imageViewByTag.setImageDrawable(imageDrawable);
- }
- }
- });
- if (cachedImage == null) {
- imageView.setImageResource(R.drawable.ic_launcher);
- }else{
- imageView.setImageDrawable(cachedImage);
- }
- // Set the text on the TextView
- TextView textView = viewCache.getTextView();
- textView.setText(imageAndText.getText());
- return rowView;
- }
- }
四、ViewCache 即ListView的每一个Item
- package com.ning.lazytest;
- import android.view.View;
- import android.widget.ImageView;
- import android.widget.TextView;
- public class ViewCache {
- private View baseView;
- private TextView textView;
- private ImageView imageView;
- public ViewCache(View baseView) {
- this.baseView = baseView;
- }
- public TextView getTextView() {
- if (textView == null) {
- textView = (TextView) baseView.findViewById(R.id.text);
- }
- return textView;
- }
- public ImageView getImageView() {
- if (imageView == null) {
- imageView = (ImageView) baseView.findViewById(R.id.image);
- }
- return imageView;
- }
- }
五、Java Bean -> ImageAndText
- package com.ning.lazytest;
- public class ImageAndText {
- private String imageUrl;
- private String text;
- public ImageAndText(String imageUrl, String text) {
- this.imageUrl = imageUrl;
- this.text = text;
- }
- public String getImageUrl() {
- return imageUrl;
- }
- public String getText() {
- return text;
- }
- }
六、Activity
- package com.ning.lazytest;
- import java.util.ArrayList;
- import java.util.List;
- import android.app.Activity;
- import android.os.Bundle;
- import android.widget.ListView;
- public class LazyLoadActivity extends Activity {
- private String[] myPicUrl = new String[]{
- "http://imguxv.penshow.cn/uploadfile/2010/04/06/thumb/thumb_250_0_20100406094922546.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/06/thumb/thumb_250_0_20100406095559309.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/06/thumb/thumb_250_0_20100406094916270.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/06/thumb/thumb_250_0_20100406085150824.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/18/thumb/thumb_250_0_20100418061054239.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/18/thumb/thumb_250_0_20100418052701708.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/18/thumb/thumb_250_0_20100418050521586.jpg"
- };
- private ImageAndText imageAndText = null;
- private List<ImageAndText> imageAndTexts = null;
- private ListView listView = null;
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- imageAndTexts = new ArrayList<ImageAndText>();
- for(int i = 0;i < myPicUrl.length; i++){
- imageAndText = new ImageAndText(myPicUrl[i], "Pic " + i);
- imageAndTexts.add(imageAndText);
- imageAndText = null;
- }
- listView = (ListView)findViewById(R.id.list);
- listView.setAdapter(new ImageAndTextListAdapter(LazyLoadActivity.this, imageAndTexts, listView));
- }
- }
异步加载图片的目的只有一个:让用户体验更好
因为异步加载不利用主线程(UI线程)
一、源码结构:
二、异步图片加载器(实现异步加载的核心)
- package com.ning.lazytest;
- import java.io.IOException;
- import java.io.InputStream;
- import java.lang.ref.SoftReference;
- import java.net.MalformedURLException;
- import java.net.URL;
- import java.util.HashMap;
- import android.graphics.drawable.Drawable;
- import android.os.Handler;
- import android.os.Message;
- public class AsyncImageLoader {
- private HashMap<String, SoftReference<Drawable>> imageCache;
- public AsyncImageLoader() {
- imageCache = new HashMap<String, SoftReference<Drawable>>();
- }
- public Drawable loadDrawable(final String imageUrl, final ImageCallback imageCallback) {
- if (imageCache.containsKey(imageUrl)) {
- SoftReference<Drawable> softReference = imageCache.get(imageUrl);
- Drawable drawable = softReference.get();
- if (drawable != null) {
- return drawable;
- }
- }
- final Handler handler = new Handler() {
- public void handleMessage(Message message) {
- imageCallback.imageLoaded((Drawable) message.obj, imageUrl);
- }
- };
- new Thread() {
- @Override
- public void run() {
- Drawable drawable = loadImageFromUrl(imageUrl);
- imageCache.put(imageUrl, new SoftReference<Drawable>(drawable));
- Message message = handler.obtainMessage(0, drawable);
- handler.sendMessage(message);
- }
- }.start();
- return null;
- }
- public static Drawable loadImageFromUrl(String url) {
- URL m;
- InputStream i = null;
- try {
- m = new URL(url);
- i = (InputStream) m.getContent();
- } catch (MalformedURLException e1) {
- e1.printStackTrace();
- } catch (IOException e) {
- e.printStackTrace();
- }
- Drawable d = Drawable.createFromStream(i, "src");
- return d;
- }
- public interface ImageCallback {
- public void imageLoaded(Drawable imageDrawable, String imageUrl);
- }
- }
三、ListView适配器
- package com.ning.lazytest;
- import java.util.List;
- import com.ning.lazytest.AsyncImageLoader.ImageCallback;
- import android.app.Activity;
- import android.graphics.drawable.Drawable;
- import android.view.LayoutInflater;
- import android.view.View;
- import android.view.ViewGroup;
- import android.widget.ArrayAdapter;
- import android.widget.ImageView;
- import android.widget.ListView;
- import android.widget.TextView;
- public class ImageAndTextListAdapter extends ArrayAdapter<ImageAndText>{
- private ListView listView;
- private AsyncImageLoader asyncImageLoader;
- public ImageAndTextListAdapter(Activity activity, List<ImageAndText> imageAndTexts, ListView listView) {
- super(activity, 0, imageAndTexts);
- this.listView = listView;
- asyncImageLoader = new AsyncImageLoader();
- }
- public View getView(int position, View convertView, ViewGroup parent) {
- Activity activity = (Activity) getContext();
- // Inflate the views from XML
- View rowView = convertView;
- ViewCache viewCache;
- if (rowView == null) {
- LayoutInflater inflater = activity.getLayoutInflater();
- rowView = inflater.inflate(R.layout.image_and_text_row, null);
- viewCache = new ViewCache(rowView);
- rowView.setTag(viewCache);
- } else {
- viewCache = (ViewCache) rowView.getTag();
- }
- ImageAndText imageAndText = getItem(position);
- // Load the image and set it on the ImageView
- String imageUrl = imageAndText.getImageUrl();
- ImageView imageView = viewCache.getImageView();
- imageView.setTag(imageUrl);
- Drawable cachedImage = asyncImageLoader.loadDrawable(imageUrl, new ImageCallback() {
- public void imageLoaded(Drawable imageDrawable, String imageUrl) {
- ImageView imageViewByTag = (ImageView) listView.findViewWithTag(imageUrl);
- if (imageViewByTag != null) {
- imageViewByTag.setImageDrawable(imageDrawable);
- }
- }
- });
- if (cachedImage == null) {
- imageView.setImageResource(R.drawable.ic_launcher);
- }else{
- imageView.setImageDrawable(cachedImage);
- }
- // Set the text on the TextView
- TextView textView = viewCache.getTextView();
- textView.setText(imageAndText.getText());
- return rowView;
- }
- }
四、ViewCache 即ListView的每一个Item
- package com.ning.lazytest;
- import android.view.View;
- import android.widget.ImageView;
- import android.widget.TextView;
- public class ViewCache {
- private View baseView;
- private TextView textView;
- private ImageView imageView;
- public ViewCache(View baseView) {
- this.baseView = baseView;
- }
- public TextView getTextView() {
- if (textView == null) {
- textView = (TextView) baseView.findViewById(R.id.text);
- }
- return textView;
- }
- public ImageView getImageView() {
- if (imageView == null) {
- imageView = (ImageView) baseView.findViewById(R.id.image);
- }
- return imageView;
- }
- }
五、Java Bean -> ImageAndText
- package com.ning.lazytest;
- public class ImageAndText {
- private String imageUrl;
- private String text;
- public ImageAndText(String imageUrl, String text) {
- this.imageUrl = imageUrl;
- this.text = text;
- }
- public String getImageUrl() {
- return imageUrl;
- }
- public String getText() {
- return text;
- }
- }
六、Activity
- package com.ning.lazytest;
- import java.util.ArrayList;
- import java.util.List;
- import android.app.Activity;
- import android.os.Bundle;
- import android.widget.ListView;
- public class LazyLoadActivity extends Activity {
- private String[] myPicUrl = new String[]{
- "http://imguxv.penshow.cn/uploadfile/2010/04/06/thumb/thumb_250_0_20100406094922546.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/06/thumb/thumb_250_0_20100406095559309.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/06/thumb/thumb_250_0_20100406094916270.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/06/thumb/thumb_250_0_20100406085150824.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/18/thumb/thumb_250_0_20100418061054239.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/18/thumb/thumb_250_0_20100418052701708.jpg",
- "http://imguxv.penshow.cn/uploadfile/2010/04/18/thumb/thumb_250_0_20100418050521586.jpg"
- };
- private ImageAndText imageAndText = null;
- private List<ImageAndText> imageAndTexts = null;
- private ListView listView = null;
- @Override
- public void onCreate(Bundle savedInstanceState) {
- super.onCreate(savedInstanceState);
- setContentView(R.layout.main);
- imageAndTexts = new ArrayList<ImageAndText>();
- for(int i = 0;i < myPicUrl.length; i++){
- imageAndText = new ImageAndText(myPicUrl[i], "Pic " + i);
- imageAndTexts.add(imageAndText);
- imageAndText = null;
- }
- listView = (ListView)findViewById(R.id.list);
- listView.setAdapter(new ImageAndTextListAdapter(LazyLoadActivity.this, imageAndTexts, listView));
- }
- }