列表视图中的每个元素都包含文本和图像。我可以使用 JSON 从 url 获取文本并显示在列表视图中。我还可以获取图像的 url，但无法在列表中显示它们。这是我的代码：
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
lv = (ListView) findViewById(R.id.newslist);
img_url = (TextView) findViewById(R.id.iamge_url);
contactList = new ArrayList<HashMap<String, Object>>();
new GetContacts().execute();
}
private class GetContacts extends AsyncTask<Void, Void, Void> {
protected Void doInBackground(Void... arg0) {
// Creating service handler class instance
ServiceHandler sh = new ServiceHandler();
// Making a request to url and getting response
String jsonStr = sh.makeServiceCall(url, ServiceHandler.GET);
Log.d("Response: ", "> " + jsonStr);
if (jsonStr != null) {
try {
JSONObject jsonObj = new JSONObject(jsonStr);
// Getting JSON Array node
contacts = jsonObj.getJSONArray(TAG_POSTS);
// looping through All Contacts
for (int i = 0; i < contacts.length(); i++) {
// JSONObject c = contacts.getJSONObject(i);
JSONObject posts = contacts.getJSONObject(i);
JSONArray attachment = posts.getJSONArray("attachments");
for (int j = 0; j< attachment.length(); j++){
JSONObject obj = attachment.getJSONObject(j);
JSONObject image = obj.getJSONObject("images");
JSONObject image_small = image.getJSONObject("tie-small");
String imgurl = image_small.getString("url");
Bitmap picture = getBitmapFromURL(imgurl);
HashMap<String, Object> contact = new HashMap<String, Object>();
contact.put("image_url", imgurl); //this image i want to load
contact.put("icon", picture); //this displays fine
contact.put(TAG_TITLE, title); // this displays fine
contactList.add(contact);
}
}
protected void onPostExecute(Void result) {
super.onPostExecute(result);
ListAdapter adapter = new SimpleAdapter(MainActivity.this, contactList, R.layout.third_row,
new String[] {"image_url",TAG_TITLE,"icon"},
new int[] {R.id.iamge_url,R.id.headline3,R.id.imageicon});
lv.setAdapter(adapter);
}
} catch (JSONException e) {
e.printStackTrace();
}
} else {
Log.e("ServiceHandler", "Couldn't get any data from the url");
}
return null;
}
这是我的方法 getBitmapFromURL() 用于从 url 获取图像：
public static Bitmap getBitmapFromURL(String src) {
try {
Log.e("src",src);
URL url = new URL(src);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setDoInput(true);
connection.connect();
InputStream input = connection.getInputStream();
Bitmap myBitmap = BitmapFactory.decodeStream(input);
Log.e("Bitmap","returned");
return myBitmap;
} catch (IOException e) {
e.printStackTrace();
Log.e("Exception",e.getMessage());
return null;
}
}
没有错误。应用程序也不会崩溃，但在列表视图中不会显示图像。我在 logcat 中收到错误消息：
unable to decode stream java.io.filenotfoundexception /android.graphics.bitmap (no such file or directory)
我检查了网址。这是工作。我可以使用 url 在浏览器中查看图像。不知道问题出在哪里。
首先从JSON中获取imageUrl，并使用此方法将其转换为位图。
public static Bitmap getBitmap(String imageUrl)
{
if (imageUrl != null && !imageUrl.equals("null"))
{
Bitmap bmp = null;
try
{
URL url = new URL(imageUrl);
bmp = BitmapFactory.decodeStream(url.openConnection().getInputStream());
} catch (MalformedURLException mue)
{
Log.e("Get Thumbnail", "Error retrieving thumbnail");
mue.printStackTrace();
} catch (IOException io)
{
Log.e("Get Thumbnail", "Error retrieving thumbnail");
io.printStackTrace();
}
return bmp;
}
return null;
}
使用它来调整大小（尽管您也可以使用imageview的XML属性来缩放和调整大小）
public static Bitmap getResizedBitmap(Bitmap image)
{
return Bitmap.createScaledBitmap(image, 175, 175, true);
}
然后在列表视图适配器的
getView() // Scale and set the Image
if (myArrayList.get(position).getImage() == null)
{
// set default image if there is no image
imgThumbnail.setImageResource(R.drawable.placeholder);
} else {
imgThumbnail.setImageBitmap(myArrayList.get(position).getImage());
}
您正在从 json 正确获取 URL...使用该 URL 您可以加载您的图像...
首先在AndroidMenifest.xml中添加以下权限
<!-- Internet Permissions -->
<uses-permission android:name="android.permission.INTERNET" />
<!-- Permission to write to external storage -->
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
然后
AndroidLoadImageFromURLActivity.java
package com.example.imagefromurl;
import android.app.Activity;
import android.os.Bundle;
import android.widget.ImageView;
public class AndroidLoadImageFromURLActivity extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
// Loader image - will be shown before loading image
int loader = R.drawable.loader;
// Imageview to show
ImageView image = (ImageView) findViewById(R.id.image);
// Image url
String image_url = "http://api.androidhive.info/images/sample.jpg";
// ImageLoader class instance
ImageLoader imgLoader = new ImageLoader(getApplicationContext());
// whenever you want to load an image from url
// call DisplayImage function
// url - image url to load
// loader - loader image, will be displayed before getting image
// image - ImageView
imgLoader.DisplayImage(image_url, loader, image);
}
}
还有 ImageLoader 类..
//ImageLoader.java
package com.example.imagefromurl;
//import statement
public class ImageLoader {
MemoryCache memoryCache=new MemoryCache();
FileCache fileCache;
private Map<ImageView, String> imageViews=Collections.synchronizedMap(new WeakHashMap<ImageView, String>());
ExecutorService executorService;
public ImageLoader(Context context){
fileCache=new FileCache(context);
executorService=Executors.newFixedThreadPool(5);
}
int stub_id = R.drawable.ic_launcher;
public void DisplayImage(String url, int loader, ImageView imageView)
{
stub_id = loader;
imageViews.put(imageView, url);
Bitmap bitmap=memoryCache.get(url);
if(bitmap!=null)
imageView.setImageBitmap(bitmap);
else
{
queuePhoto(url, imageView);
imageView.setImageResource(loader);
}
}
private void queuePhoto(String url, ImageView imageView)
{
PhotoToLoad p=new PhotoToLoad(url, imageView);
executorService.submit(new PhotosLoader(p));
}
private Bitmap getBitmap(String url)
{
File f=fileCache.getFile(url);
//from SD cache
Bitmap b = decodeFile(f);
if(b!=null)
return b;
//from web
try {
Bitmap bitmap=null;
URL imageUrl = new URL(url);
HttpURLConnection conn = (HttpURLConnection)imageUrl.openConnection();
conn.setConnectTimeout(30000);
conn.setReadTimeout(30000);
conn.setInstanceFollowRedirects(true);
InputStream is=conn.getInputStream();
OutputStream os = new FileOutputStream(f);
Utils.CopyStream(is, os);
os.close();
bitmap = decodeFile(f);
return bitmap;
} catch (Exception ex){
ex.printStackTrace();
return null;
}
}
//decodes image and scales it to reduce memory consumption
private Bitmap decodeFile(File f){
try {
//decode image size
BitmapFactory.Options o = new BitmapFactory.Options();
o.inJustDecodeBounds = true;
BitmapFactory.decodeStream(new FileInputStream(f),null,o);
//Find the correct scale value. It should be the power of 2.
final int REQUIRED_SIZE=70;
int width_tmp=o.outWidth, height_tmp=o.outHeight;
int scale=1;
while(true){
if(width_tmp/2<REQUIRED_SIZE || height_tmp/2<REQUIRED_SIZE)
break;
width_tmp/=2;
height_tmp/=2;
scale*=2;
}
//decode with inSampleSize
BitmapFactory.Options o2 = new BitmapFactory.Options();
o2.inSampleSize=scale;
return BitmapFactory.decodeStream(new FileInputStream(f), null, o2);
} catch (FileNotFoundException e) {}
return null;
}
//Task for the queue
private class PhotoToLoad
{
public String url;
public ImageView imageView;
public PhotoToLoad(String u, ImageView i){
url=u;
imageView=i;
}
}
class PhotosLoader implements Runnable {
PhotoToLoad photoToLoad;
PhotosLoader(PhotoToLoad photoToLoad){
this.photoToLoad=photoToLoad;
}
@Override
public void run() {
if(imageViewReused(photoToLoad))
return;
Bitmap bmp=getBitmap(photoToLoad.url);
memoryCache.put(photoToLoad.url, bmp);
if(imageViewReused(photoToLoad))
return;
BitmapDisplayer bd=new BitmapDisplayer(bmp, photoToLoad);
Activity a=(Activity)photoToLoad.imageView.getContext();
a.runOnUiThread(bd);
}
}
boolean imageViewReused(PhotoToLoad photoToLoad){
String tag=imageViews.get(photoToLoad.imageView);
if(tag==null || !tag.equals(photoToLoad.url))
return true;
return false;
}
//Used to display bitmap in the UI thread
class BitmapDisplayer implements Runnable
{
Bitmap bitmap;
PhotoToLoad photoToLoad;
public BitmapDisplayer(Bitmap b, PhotoToLoad p){bitmap=b;photoToLoad=p;}
public void run()
{
if(imageViewReused(photoToLoad))
return;
if(bitmap!=null)
photoToLoad.imageView.setImageBitmap(bitmap);
else
photoToLoad.imageView.setImageResource(stub_id);
}
}
public void clearCache() {
memoryCache.clear();
fileCache.clear();
}
}
此代码都可以在这里找到。