我需要包含一个搜索功能，供用户搜索列表视图。
这是我的MainActivity.java
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// URL to the JSON data
String strUrl = "http://10.0.2.2/get_stores.php";
// 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);
searchBox = (EditText)findViewById(R.id.searchBox);
}
/** 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:", 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]);
StoreJSONParser countryJsonParser = new StoreJSONParser();
countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("JSON Exception1",e.toString());
}
// Instantiating json parser class
StoreJSONParser countryJsonParser = new StoreJSONParser();
// A list object to store the parsed countries list
List<HashMap<String, Object>> countries = null;
try{
// Getting the parsed data as a List construct
countries = countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
// Keys used in Hashmap
String[] from = { "country","flag","details"};
// Ids of views in listview_layout
int[] to = { R.id.storename,R.id.icon,R.id.details};
// Instantiating an adapter to store each items
// R.layout.listview_layout defines the layout of each item
adapter = new SimpleAdapter(getBaseContext(), countries, R.layout.restaurant_list, 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);
met_search();
for(int i=0;i<adapter.getCount();i++){
HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(i);
String imgUrl = (String) hm.get("flag_path");
ImageLoaderTask imageLoaderTask = new ImageLoaderTask();
HashMap<String, Object> hmDownload = new HashMap<String, Object>();
hm.put("flag_path",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("flag_path");
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() + "/wpta_"+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("flag",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("flag");
// 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("flag",path);
// Noticing listview about the dataset changes
adapter.notifyDataSetChanged();
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
//getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
private void met_search() {
// TODO Auto-generated method stub
/**
* Enabling Search Filter
* */
searchBox.addTextChangedListener(new TextWatcher() {
public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
}
public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,
int arg3) {
// TODO Auto-generated method stub
}
public void afterTextChanged(Editable arg0) {
// TODO Auto-generated method stub
MainActivity.this.adapter.getFilter().filter(arg0);
}
});
}
这是JSONParser.java
public class StoreJSONParser {
// Receives a JSONObject and returns a list
public List<HashMap<String,Object>> parse(JSONObject jObject){
JSONArray jCountries = null;
try {
// Retrieves all the elements in the 'countries' array
jCountries = jObject.getJSONArray("storelistfood");
} catch (JSONException e) {
e.printStackTrace();
}
// Invoking getCountries with the array of json object
// where each json object represent a country
return getCountries(jCountries);
}
private List<HashMap<String, Object>> getCountries(JSONArray jCountries){
int countryCount = jCountries.length();
List<HashMap<String, Object>> countryList = new ArrayList<HashMap<String,Object>>();
HashMap<String, Object> country = null;
// Taking each country, parses and adds to list object
for(int i=0; i<countryCount;i++){
try {
// Call getCountry with country JSON object to parse the country
country = getCountry((JSONObject)jCountries.get(i));
countryList.add(country);
} catch (JSONException e) {
e.printStackTrace();
}
}
return countryList;
}
// Parsing the Country JSON object
private HashMap<String, Object> getCountry(JSONObject jCountry){
HashMap<String, Object> country = new HashMap<String, Object>();
String countryName = "";
String flag="";
/*String language = "";
String capital = "";
String currencyCode = "";
String currencyName = "";*/
try {
countryName = jCountry.getString("STORENAME");
flag = jCountry.getString("logo");
/*language = jCountry.getString("language");
capital = jCountry.getString("capital");
currencyCode = jCountry.getJSONObject("currency").getString("code");
currencyName = jCountry.getJSONObject("currency").getString("currencyname");*/
/*String details = "Language : " + language + "\n"; +
"Capital : " + capital + "\n" +
"Currency : " + currencyName + "(" + currencyCode + ")";*/
country.put("country", countryName);
country.put("flag", R.drawable.ninety_six);
country.put("flag_path", flag);
//country.put("details", details);
} catch (JSONException e) {
e.printStackTrace();
}
return country;
}
这是我从logcat获得的错误
java.lang.NullPointerException
at android.widget.SimpleAdapter.getCount(SimpleAdapter.java:93)
at android.widget.AdapterView.checkFocus(AdapterView.java:713)
at android.widget.AdapterView$AdapterDataSetObserver.onInvalidated(AdapterView.java:836)
at android.widget.AbsListView$AdapterDataSetObserver.onInvalidated(AbsListView.java:6288)
at android.database.DataSetObservable.notifyInvalidated(DataSetObservable.java:50)
at android.widget.BaseAdapter.notifyDataSetInvalidated(BaseAdapter.java:59)
at android.widget.SimpleAdapter$SimpleFilter.publishResults(SimpleAdapter.java:383)
at android.widget.Filter$ResultsHandler.handleMessage(Filter.java:282)
我只需要用户通过提供的edittext框搜索列表视图。我已经尝试了谷歌的许多解决方案，但它不适用于我的情况。
答案 0 :(得分：0)
您获得的NPE是由此引起的：
at android.widget.SimpleAdapter.getCount(SimpleAdapter.java:93)
基本上说SimpleAdapter下的项目是null。
通过检查MainActivity中的这一行，确保JSON解析器中的返回项不为空：
try{
if(countryJsonParser.parse(jObject) != null) {
countries = countryJsonParser.parse(jObject);
}
}catch(Exception e){
Log.d("Exception",e.toString());
}