我正在使用http请求获取JSON格式的数据，该格式也会加载图片。我正在尝试实现onTextChanged函数，但每当我在EditText框中输入任何字母时，它总会崩溃。
/** AsyncTask to parse json data and load ListView */
private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{
// 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();
try{
// Getting the parsed data as a List construct
countries = countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
// 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;
}
onPostExecute
protected void onPostExecute(SimpleAdapter adapter) {
// Setting adapter for the listview
adapter = new SimpleAdapter(getBaseContext(), countries, R.layout.restaurant_list, from, to);
Log.d("What is country", String.valueOf(countries));
mListView.setAdapter(adapter);
searchBox = (EditText)findViewById(R.id.searchBox);
searchBox.addTextChangedListener(new TextWatcher() {
public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
// When user changed the Text
ChooseCategory.this.adapter.getFilter().filter(cs);
}
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
//ChooseCategory.this.adapter.getFilter().filter(arg0);
}
});
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);
}
}
}
来自logcat的错误：
java.lang.NullPointerException
at ChooseCategory$ListViewLoaderTask$1.onTextChanged(ChooseCategory.java:196)
at android.widget.TextView.sendOnTextChanged(TextView.java:7408)
at android.widget.TextView.handleTextChanged(TextView.java:7467)
at android.widget.TextView$ChangeWatcher.onTextChanged(TextView.java:9183)
at android.text.SpannableStringBuilder.sendTextChanged(SpannableStringBuilder.java:962)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:496)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:435)
at android.text.SpannableStringBuilder.replace(SpannableStringBuilder.java:30)
at android.text.method.QwertyKeyListener.onKeyDown(QwertyKeyListener.java:223)
at android.text.method.TextKeyListener.onKeyDown(TextKeyListener.java:136)
at android.widget.TextView.doKeyDown(TextView.java:5532)
at android.widget.TextView.onKeyDown(TextView.java:5343)
at android.view.KeyEvent.dispatch(KeyEvent.java:2640)
at android.view.View.dispatchKeyEvent(View.java:7665)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1408)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1408)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1408)
at android.view.ViewGroup.dispatchKeyEvent(ViewGroup.java:1408)
at com.android.internal.policy.impl.PhoneWindow$DecorView.superDispatchKeyEvent(PhoneWindow.java:2035)
at com.android.internal.policy.impl.PhoneWindow.superDispatchKeyEvent(PhoneWindow.java:1505)
at android.app.Activity.dispatchKeyEvent(Activity.java:2418)
at com.android.internal.policy.impl.PhoneWindow$DecorView.dispatchKeyEvent(PhoneWindow.java:1962)
at android.view.ViewRootImpl$ViewPostImeInputStage.processKeyEvent(ViewRootImpl.java:3852)
at android.view.ViewRootImpl$ViewPostImeInputStage.onProcess(ViewRootImpl.java:3826)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3399)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3449)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3418)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3525)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3426)
at android.view.ViewRootImpl$AsyncInputStage.apply(ViewRootImpl.java:3582)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3399)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3449)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3418)
at android.view.ViewRootImpl$InputStage.apply(ViewRootImpl.java:3426)
at android.view.ViewRootImpl$InputStage.deliver(ViewRootImpl.java:3399)
at android.view.ViewRootImpl$InputStage.onDeliverToNext(ViewRootImpl.java:3449)
at android.view.ViewRootImpl$InputStage.forward(ViewRootImpl.java:3418)
at android.view.ViewRootImpl$AsyncInputStage.forward(ViewRootImpl.java:3558)
at android.view.ViewRootImpl$ImeInputStage.onFinishedInputEvent(ViewRootImpl.java:3718)
at android.view.inputmethod.InputMethodManager$PendingEvent.run(InputMethodManager.java:2010)
at android.view.inputmethod.InputMethodManager.invokeFinishedInputEventCallback(InputMethodManager.java:1704)
at android.view.inputmethod.InputMethodManager.finishedInputEvent(InputMethodManager.java:1695)
at android.view.inputmethod.InputMethodManager$ImeInputEventSender.onInputEventFinished(InputMethodManager.java:1987)
at android.view.InputEventSender.dispatchInputEventFinished(InputEventSender.java:141)
at android.os.MessageQueue.nativePollOnce(Native Method)
at android.os.MessageQueue.next(MessageQueue.java:138)
at android.os.Looper.loop(Looper.java:123)
at android.app.ActivityThread.main(ActivityThread.java:5017)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:515)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
at dalvik.system.NativeStart.main(Native Method)
java.lang.NullPointerException
at ChooseCategory$ListViewLoaderTask$1.onTextChanged
请不要将其作为副本。我看过那篇帖子，我仍然无法修复它。这就是我在这里发帖的原因。
这是ChooseCategory.java的完整代码
public class ChooseCategory extends Activity {
ListView mListView;
EditText searchBox;
SimpleAdapter adapter;
JSONObject jObject;
StoreJSONParser countryJsonParser = new StoreJSONParser();
// A list object to store the parsed countries list
List<HashMap<String, Object>> countries = null;
// 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};
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Getting a reference to ListView of activity_main
mListView = (ListView) findViewById(R.id.list);
// 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);
}
/** 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>{
// 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();
try{
// Getting the parsed data as a List construct
countries = countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
// 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
adapter = new SimpleAdapter(getBaseContext(), countries, R.layout.restaurant_list, from, to);
Log.d("What is country", String.valueOf(countries));
mListView.setAdapter(adapter);
searchBox = (EditText)findViewById(R.id.searchBox);
searchBox.addTextChangedListener(new TextWatcher() {
public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
// When user changed the Text
ChooseCategory.this.adapter.getFilter().filter(cs);
}
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
//ChooseCategory.this.adapter.getFilter().filter(arg0);
}
});
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;
}
}
答案 0 :(得分：0)
你有一个名为adapter的类变量吗？ 似乎ChooseCategory.this.adapter不是局部变量 adapter = new SimpleAdapter（getBaseContext（），countries，R.layout.restaurant_list，from，to）;
你应该命名类变量mAdapter。
答案 1 :(得分：0)
按如下方式更改Asyn类：
private class ListViewLoaderTask extends AsyncTask<String, Void, String>{ **//Change SimpleAdapter to String**
// Doing the parsing of xml data in a non-ui thread
@Override **//Change SimpleAdapter to String**
protected String 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();
try{
// Getting the parsed data as a List construct
countries = countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
// 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 null;
}
/** Invoked by the Android on "doInBackground" is executed */
@Override **//Change SimpleAdapter to String**
protected void onPostExecute(String result) {
// Setting adapter for the listview
adapter = new SimpleAdapter(ChooseCategory.this, countries, R.layout.restaurant_list, from, to);
Log.d("What is country", String.valueOf(countries));
mListView.setAdapter(adapter);
searchBox = (EditText)findViewById(R.id.searchBox);
searchBox.addTextChangedListener(new TextWatcher() {
public void onTextChanged(CharSequence cs, int arg1, int arg2, int arg3) {
// When user changed the Text
adapter.getFilter().filter(cs);
}
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
//ChooseCategory.this.adapter.getFilter().filter(arg0);
}
});
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);
}
}
}
答案 2 :(得分：0)
我认为您的edittext初始化存在问题。
searchBox = (EditText)findViewById(R.id.searchBox);
将此行从onPostexcute()移至OnCreate()