我正在尝试提高应用程序性能下载缩略图以填充列表视图，然后，如果用户选择项目，则显示更大的分辨率图像。
想法是在listview上编写图像网址，并将值传递给详细活动，并在那里管理下载。
只使用一个图像，应用程序运行正常，但我不喜欢使用单个图像获得的结果。
在下面的代码中，添加的行前面有注释：
ListView显示所有带缩略图的项目
public class ListViewCategory extends Activity {
private static final String TAG = "ListViewCategory: ";
ListView mListView;
String strUrl;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.listview_category_layout);
// URL to the JSON data
Intent iN = getIntent();
Bundle b = iN.getExtras();
if (b!=null){
strUrl=(String)b.get("urlJSON");
}
// Creating a new non-ui thread task to download json data
DownloadTask downloadTask = new DownloadTask();
// Starting the download process
downloadTask.execute(strUrl);
// Getting a reference to ListView of activity_main
mListView = (ListView) findViewById(R.id.list);
mListView.setOnItemClickListener(new OnItemClickListener(){
public void onItemClick(AdapterView<?> parent, View view, int position, long id){
//get brand from listview
TextView marcaDetail = (TextView) view.findViewById(R.id.marcas);
String marcaToDetail = marcaDetail.getText().toString();
//get model from listview
TextView modeloDetail = (TextView) view.findViewById(R.id.modelos);
String modeloToDetail = modeloDetail.getText().toString();
//get photoUrl from listview
TextView urlDetail = (TextView) view.findViewById(R.id.tvUrl);
String urlToDetail = urlDetail.getText().toString();
//get price from listview
TextView priceDetail = (TextView) view.findViewById(R.id.precios);
String priceToDetail = priceDetail.getText().toString();
Intent iPosition = new Intent(view.getContext(),DetailViewItem.class);
iPosition.putExtra("marca", marcaToDetail);
iPosition.putExtra("photoDetail", urlToDetail);
iPosition.putExtra("modelo", modeloToDetail);
iPosition.putExtra("precio", priceToDetail);
startActivity(iPosition);
Toast.makeText(ListViewCategory.this,urlToDetail.toString() , Toast.LENGTH_LONG).show();
}
});
}
/** A method to download json data from url */
private String downloadUrl(String strUrl) throws IOException{
String data = "";
InputStream iStream = null;
try{
URL url = new URL(strUrl);
// Creating an http connection to communicate with url
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
// Reading data from url
iStream = urlConnection.getInputStream();
BufferedReader br = new BufferedReader(new InputStreamReader(iStream));
StringBuffer sb = new StringBuffer();
String line = "";
while( ( line = br.readLine()) != null){
sb.append(line);
}
data = sb.toString();
br.close();
}catch(Exception e){
Log.d("Exception while downloading url", e.toString());
}finally{
iStream.close();
}
return data;
}
/** AsyncTask to download json data */
private class DownloadTask extends AsyncTask<String, Integer, String>{
String data = null;
@Override
protected String doInBackground(String... url) {
try{
data = downloadUrl(url[0]);
}catch(Exception e){
Log.d("Background Task",e.toString());
}
return data;
}
@Override
protected void onPostExecute(String result) {
// The parsing of the xml data is done in a non-ui thread
ListViewLoaderTask listViewLoaderTask = new ListViewLoaderTask();
// Start parsing xml data
listViewLoaderTask.execute(result);
}
}
/** AsyncTask to parse json data and load ListView */
private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{
JSONObject jObject;
// Doing the parsing of xml data in a non-ui thread
@Override
protected SimpleAdapter doInBackground(String... strJson) {
try{
jObject = new JSONObject(strJson[0]);
JSONParser jsonParser = new JSONParser();
jsonParser.parse(jObject);
}catch(Exception e){
Log.d("JSON Exception1",e.toString());
}
// Instantiating json parser class
JSONParser jsonParser = new JSONParser();
// A list object to store the parsed items list
List<HashMap<String, Object>> brands = null;
try{
// Getting the parsed data as a List construct
brands = jsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
// Keys used in Hashmap
//added
String[] from = { "foto","marca","modelo","precio","detail"};
// Ids of views in list_v layout
int[] to = { R.id.fotos,R.id.marcas,R.id.modelos,R.id.precios,R.id.tvUrl};
// Instantiating an adapter to store each items
// R.layout.list_v defines the layout of each item
SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), brands, R.layout.list_v, from, to);
return adapter;
}
/** Invoked by the Android on "doInBackground" is executed */
@Override
protected void onPostExecute(SimpleAdapter adapter) {
// Setting adapter for the listview
mListView.setAdapter(adapter);
for(int i=0;i<adapter.getCount();i++){
HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(i);
String imgUrl = (String) hm.get("photoUrl");
Log.i(TAG, imgUrl);
ImageLoaderTask imageLoaderTask = new ImageLoaderTask();
HashMap<String, Object> hmDownload = new HashMap<String, Object>();
hm.put("photoUrl",imgUrl);
hm.put("position", i);
// Starting ImageLoaderTask to download and populate image in the listview
imageLoaderTask.execute(hm);
}
}
}
/** AsyncTask to download and load an image in ListView */
private class ImageLoaderTask extends AsyncTask<HashMap<String, Object>, Void, HashMap<String, Object>>{
@Override
protected HashMap<String, Object> doInBackground(HashMap<String, Object>... hm) {
InputStream iStream=null;
String imgUrl = (String) hm[0].get("photoUrl");
int position = (Integer) hm[0].get("position");
URL url;
try {
url = new URL(imgUrl);
// Creating an http connection to communicate with url
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
// Connecting to url
urlConnection.connect();
// Reading data from url
iStream = urlConnection.getInputStream();
// Getting Caching directory
File cacheDirectory = getBaseContext().getCacheDir();
// Temporary file to store the downloaded image
File tmpFile = new File(cacheDirectory.getPath() + "/lakari_"+position+".png");
// The FileOutputStream to the temporary file
FileOutputStream fOutStream = new FileOutputStream(tmpFile);
// Creating a bitmap from the downloaded inputstream
Bitmap b = BitmapFactory.decodeStream(iStream);
// Writing the bitmap to the temporary file as png file
b.compress(Bitmap.CompressFormat.PNG,100, fOutStream);
// Flush the FileOutputStream
fOutStream.flush();
//Close the FileOutputStream
fOutStream.close();
// Create a hashmap object to store image path and its position in the listview
HashMap<String, Object> hmBitmap = new HashMap<String, Object>();
// Storing the path to the temporary image file
hmBitmap.put("foto",tmpFile.getPath());
// Storing the position of the image in the listview
hmBitmap.put("position",position);
// Returning the HashMap object containing the image path and position
return hmBitmap;
}catch (Exception e) {
e.printStackTrace();
}
return null;
}
@Override
protected void onPostExecute(HashMap<String, Object> result) {
// Getting the path to the downloaded image
String path = (String) result.get("foto");
// Getting the position of the downloaded image
int position = (Integer) result.get("position");
// Getting adapter of the listview
SimpleAdapter adapter = (SimpleAdapter ) mListView.getAdapter();
// Getting the hashmap object at the specified position of the listview
HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(position);
// Overwriting the existing path in the adapter
hm.put("foto",path);
// Noticing listview about the dataset changes
adapter.notifyDataSetChanged();
}
}
}
ListViewCategory布局：
<RelativeLayout 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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".ListViewCategory"
android:background="#000000">
<TextView
android:id="@+id/textview"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center">
</TextView>
<ListView
android:id="@+id/list"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:divider="#e600e6"
android:dividerHeight="0.2sp"/>
</RelativeLayout>
ListView单元格：
<LinearLayout
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:layout_weight="1"
android:orientation="vertical"
android:background="#a8a8a8" >
<ImageView
android:id="@+id/fotos"
android:layout_width="wrap_content"
android:layout_height="match_parent"
android:contentDescription="@string/description"
android:src="@drawable/ic_launcher" />
<!--
<TextView
android:id="@+id/tvUrl"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textColor="#aaaaaa"
android:textSize="6sp"/>
-->
</LinearLayout>
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="2" >
<TextView
android:id="@+id/tvUrl"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:textColor="#aaaaaa"
android:textSize="12sp"/>
<TextView
android:id="@+id/marcas"
android:textSize="14sp"
android:textColor="#aaaaaa"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_gravity="left"
/>
<TextView
android:id="@+id/modelos"
android:textSize="22sp"
android:textColor="#e600e6"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="center"
/>
<TextView
android:id="@+id/precios"
android:textSize="16sp"
android:textColor="#aaaaab"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:gravity="right"
/>
</LinearLayout>
</LinearLayout>
JSON解析器：
/** A class to parse json data */
public class JSONParser {
// Receives a JSONObject and returns a list
public List<HashMap<String,Object>> parse(JSONObject jObject){
JSONArray jItems = null;
try {
// Retrieves all the elements in the "items" array
jItems = jObject.getJSONArray("items");
} catch (JSONException e) {
e.printStackTrace();
}
return getItems(jItems);
}
private List<HashMap<String, Object>> getItems(JSONArray jItems){
int itemCount = jItems.length();
List<HashMap<String, Object>> itemList = new ArrayList<HashMap<String,Object>>();
HashMap<String, Object> item = null;
// Taking each item, parses and adds to list object
for(int i=0; i<itemCount;i++){
try {
// Call getItem with item JSON object to parse the item
item = getItem((JSONObject)jItems.get(i));
itemList.add(item);
} catch (JSONException e) {
e.printStackTrace();
}
}
return itemList;
}
// Parsing the JSON object
private HashMap<String, Object> getItem(JSONObject jItem){
HashMap<String, Object> item = new HashMap<String, Object>();
String marca = "";
String foto = "";
String modelo = "";
String precio = "";
//añadido
String detail = "";
try {
marca = jItem.getString("marca");
foto = jItem.getString("photoUrl");
modelo = jItem.getString("modelo");
precio = jItem.getString("precio");
//added
detail = jItem.getString("photoDetail");
item.put("marca", marca);
item.put("foto", R.drawable.ic_launcher);
item.put("modelo", modelo);
item.put("photoUrl", foto);
item.put("precio", precio);
//added
item.put("photoDetail", detail);
} catch (JSONException e) {
e.printStackTrace();
}
return item;
}
}
最后，细节活动我错误，没有图像，但应用程序没有崩溃：
public class DetailViewItem extends Activity{
//added
ImageView imageView;
private String photoCacheUri = "";
private String detailMarca = "";
private String detailModelo = "";
private String detailPrecio = "";
private String mailBody = "";
private String mailSubject = "";
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.detail_view_item_layout);
Intent intentDetail = getIntent();
Bundle bDetail = intentDetail.getExtras();
if (bDetail != null){
detailMarca = (String)bDetail.get("marca");
photoCacheUri = (String)bDetail.get("photoDetail");
detailModelo = (String)bDetail.getString("modelo");
detailPrecio = (String)bDetail.getString("precio");
}
//set brand
TextView textviewMarca = (TextView) findViewById(R.id.tvMarca);
textviewMarca.setText(detailMarca);
//set image
/*ImageView imageView = (ImageView) findViewById(R.id.photoDetail);
Bitmap bmImg = BitmapFactory.decodeFile(photoCacheUri);
imageView.setImageBitmap(bmImg);*/
//added
imageView= (ImageView) findViewById(R.id.photoDetail);
// Create an object for subclass of AsyncTask
GetXMLTask task = new GetXMLTask();
// Execute the task
task.execute(new String[] { photoCacheUri });
//set model
TextView textviewModelo = (TextView) findViewById(R.id.tvModelo);
textviewModelo.setText(detailModelo);
//set price
TextView textviewPrecio = (TextView) findViewById(R.id.tvPrecio);
textviewPrecio.setText(detailPrecio);
}
//added
private class GetXMLTask extends AsyncTask<String, Void, Bitmap> {
@Override
protected Bitmap doInBackground(String... urls) {
Bitmap map = null;
for (String url : urls) {
map = downloadImage(url);
}
return map;
}
// Sets the Bitmap returned by doInBackground
@Override
protected void onPostExecute(Bitmap result) {
imageView.setImageBitmap(result);
}
// Creates Bitmap from InputStream and returns it
private Bitmap downloadImage(String url) {
Bitmap bitmap = null;
InputStream stream = null;
BitmapFactory.Options bmOptions = new BitmapFactory.Options();
bmOptions.inSampleSize = 1;
try {
stream = getHttpConnection(url);
bitmap = BitmapFactory.
decodeStream(stream, null, bmOptions);
stream.close();
} catch (IOException e1) {
e1.printStackTrace();
}
return bitmap;
}
// Makes HttpURLConnection and returns InputStream
private InputStream getHttpConnection(String urlString)
throws IOException {
InputStream stream = null;
URL url = new URL(urlString);
URLConnection connection = url.openConnection();
try {
HttpURLConnection httpConnection = (HttpURLConnection) connection;
httpConnection.setRequestMethod("GET");
httpConnection.connect();
if (httpConnection.getResponseCode() == HttpURLConnection.HTTP_OK) {
stream = httpConnection.getInputStream();
}
} catch (Exception ex) {
ex.printStackTrace();
}
return stream;
}
}
}
logcat的：
12-03 04:33:12.256: W/System.err(2420): java.net.MalformedURLException: Protocol not found:
12-03 04:33:12.256: W/System.err(2420): at java.net.URL.<init>(URL.java:178)
12-03 04:33:12.266: W/System.err(2420): at java.net.URL.<init>(URL.java:127)
12-03 04:33:12.276: W/System.err(2420): at com.lupradoa.lakari.fragmenttabstudy.tabB.DetailViewItem$GetXMLTask.getHttpConnection(DetailViewItem.java:131)
12-03 04:33:12.276: W/System.err(2420): at com.lupradoa.lakari.fragmenttabstudy.tabB.DetailViewItem$GetXMLTask.downloadImage(DetailViewItem.java:117)
12-03 04:33:12.276: W/System.err(2420): at com.lupradoa.lakari.fragmenttabstudy.tabB.DetailViewItem$GetXMLTask.doInBackground(DetailViewItem.java:98)
12-03 04:33:12.276: W/System.err(2420): at com.lupradoa.lakari.fragmenttabstudy.tabB.DetailViewItem$GetXMLTask.doInBackground(DetailViewItem.java:1)
12-03 04:33:12.276: W/System.err(2420): at android.os.AsyncTask$2.call(AsyncTask.java:287)
12-03 04:33:12.276: W/System.err(2420): at java.util.concurrent.FutureTask.run(FutureTask.java:234)
12-03 04:33:12.326: W/System.err(2420): at android.os.AsyncTask$SerialExecutor$1.run(AsyncTask.java:230)
12-03 04:33:12.326: W/System.err(2420): at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1080)
12-03 04:33:12.326: W/System.err(2420): at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:573)
12-03 04:33:12.346: W/System.err(2420): at java.lang.Thread.run(Thread.java:841)
12-03 04:33:12.496: W/EGL_emulation(2420): eglSurfaceAttrib not implemented
我已经修改了很多次代码，但我找不到错误。你们有人能指出来吗？