我正在构建一个应用程序，它显示listView上的项目，包括描述，品牌，价格和图像。通过下载JSON文件来填充listView。下载图像后，进度对话框不会消失，应用程序会冻结。我需要ProgressDialog以避免用户在下载图像之前单击一个单元格。我找了一个解决方案，但没有找到答案。 编辑： 我没有错误或例外，屏幕上出现 TOAST 。 我实现进度对话框的代码：
public class ListViewCategory extends Activity {
private int jsonLength = 0;
private int control = 0;
private ProgressDialog waitingDialog;
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){
…
}
});
}
/** 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 countries 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
String[] from = { "foto","marca","modelo","precio","foto"};
// 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);
jsonLength = adapter.getCount();
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>>{
//Adding preExecute
@Override
protected void onPreExecute(){
waitingDialog = ProgressDialog.show(ListViewCategory.this, “Wait..”, "Downloading”); waitingDialog.setCancelable(true);
waitingDialog.show();
}
@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);
//Count number of images downloaded and sent to listview
control++;
Log.i(TAG_2, String.valueOf(control));
// Noticing listview about the dataset changes
adapter.notifyDataSetChanged();
if (control/jsonLength == 0){
waitingDialog.dismiss();
Toast.makeText(ListViewCategory.this, "Toast Appears. Yes...", Toast.LENGTH_SHORT).show();
}
}
}
}
请帮帮我吗？
答案 0 :(得分：0)
您将null返回到postExecute
这就是为什么你的if条件在这里变错了
if(waitingDialog != null && waitingDialog.isShowing())
{
waitingDialog.dismiss();
}
删除`doInBackground（）;
中的返回null}catch (Exception e) {
e.printStackTrace();
}
-> return null;
答案 1 :(得分：0)