Android 从JSON响应填充Gridview我在logcat中得到NullPointerException
当我试图从JSON响应中获取GridView时，logcat中出现了空点异常，任何人都可以解决这个问题。我不熟悉安卓系统Android 从JSON响应填充Gridview我在logcat中得到NullPointerException,android,json,gridview,Android,Json,Gridview,当我试图从JSON响应中获取GridView时，logcat中出现了空点异常，任何人都可以解决这个问题。我不熟悉安卓系统 public class MainActivity extends Activity { GridView mListView; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
public class MainActivity extends Activity {
GridView mListView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//view = inflater.inflate(R.layout.activity_main, null);
String strUrl = "http://globalringtools.com/android/categories.php";
DownloadTask downloadTask = new DownloadTask();
downloadTask.execute(strUrl);
mListView = (GridView) findViewById(R.id.gridView1);
}
private String downloadUrl(String strUrl) throws IOException{
String data = "";
InputStream iStream = null;
try{
URL url = new URL(strUrl);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.connect();
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;
}
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){
ListViewLoaderTask listViewLoaderTask = new ListViewLoaderTask();
listViewLoaderTask.execute(result);
}
}
private class ListViewLoaderTask extends AsyncTask<String, Void, SimpleAdapter>{
JSONObject jObject;
@Override
protected SimpleAdapter doInBackground(String... strJson){
try{
jObject = new JSONObject(strJson[0]);
CountryJSONParser countryJsonParser = new CountryJSONParser();
countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("JSON Exception1",e.toString());
}
CountryJSONParser countryJsonParser = new CountryJSONParser();
List<HashMap<String, Object>> countries = null;
try{
countries = countryJsonParser.parse(jObject);
}catch(Exception e){
Log.d("Exception",e.toString());
}
String[] from = { "flag","country"};
int[] to = { R.id.picture,R.id.text};
SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), countries, R.layout.grid_layout, from, to);
return adapter;
}
@Override
protected void onPostExecute(SimpleAdapter adapter){
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("flag_path");
ImageLoaderTask imageLoaderTask = new ImageLoaderTask();
HashMap<String, Object> hmDownload = new HashMap<String, Object>();
hm.put("flag_path",imgUrl);
hm.put("position", i);
imageLoaderTask.execute(hm);
}
}
}
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 im;
String imgUrl = (String) hm[0].get("flag_path");
int position = (Integer) hm[0].get("position");
URL url;
try{
url = new URL(imgUrl);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.connect();
iStream = urlConnection.getInputStream();
File cacheDirectory = getBaseContext().getCacheDir();
File tmpFile = new File(cacheDirectory.getPath() + "/wpta_"+position+".png");
FileOutputStream fOutStream = new FileOutputStream(tmpFile);
Bitmap b = BitmapFactory.decodeStream(iStream);
b.compress(Bitmap.CompressFormat.PNG,100, fOutStream);
fOutStream.flush();
fOutStream.close();
HashMap<String, Object> hmBitmap = new HashMap<String, Object>();
hmBitmap.put("flag",tmpFile.getPath());
hmBitmap.put("position",position);
return hmBitmap;
}catch(Exception e){
e.printStackTrace();
}
return null;
}
protected void onPostExecute(HashMap<String, Object> result){
String path = (String) result.get("flag");
int position = (Integer) result.get("position");
SimpleAdapter adapter = (SimpleAdapter ) mListView.getAdapter();
HashMap<String, Object> hm = (HashMap<String, Object>) adapter.getItem(position);
hm.put("flag",path);
adapter.notifyDataSetChanged();
}
}
}
package com.ambilobes.cust_grid;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
/** A class to parse json data */
public class CountryJSONParser {
// 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("categories");
} 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="";
StringBuilder strBuilder = new StringBuilder();
strBuilder.append("http://globalringtools.com/flowborn/template/resources/images/client_categories");
try {
strBuilder.append(jCountry.getString("image"));
flag = strBuilder.toString();
countryName = jCountry.getString("category");
country.put("country", countryName);
country.put("flag", R.drawable.blank);
country.put("flag_path", flag);
} catch (JSONException e) {
e.printStackTrace();
}
return country;
}
}
有人能帮我吗。无论您的图像加载程序第145行中有什么内容，都是问题所在。响应是否不为空？您尝试访问的网站可能为空
protected void onPostExecute(HashMap<String, Object> result){
if (result != null) {
...
}
}
try{
url = new URL(imgUrl);
HttpURLConnection urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.connect();
iStream = urlConnection.getInputStream();
File cacheDirectory = getBaseContext().getCacheDir();
File tmpFile = new File(cacheDirectory.getPath() + "/wpta_"+position+".png");
FileOutputStream fOutStream = new FileOutputStream(tmpFile);
Bitmap b = BitmapFactory.decodeStream(iStream);
b.compress(Bitmap.CompressFormat.PNG,100, fOutStream);
fOutStream.flush();
fOutStream.close();
HashMap<String, Object> hmBitmap = new HashMap<String, Object>();
hmBitmap.put("flag",tmpFile.getPath());
hmBitmap.put("position",position);
return hmBitmap;
}catch(Exception e){
e.printStackTrace();
}
DownloadTask downloadTask = new DownloadTask();
downloadTask.execute(strUrl);
mListView = (GridView) findViewById(R.id.gridView1);
mListView = (GridView) findViewById(R.id.gridView1);
DownloadTask downloadTask = new DownloadTask();
downloadTask.execute(strUrl);
请输入您的日志详细信息。01-23 10:07:59.358:E/AndroidRuntime28335：致命异常：main 01-23 10:07:59.358:E/AndroidRuntime28335:java.lang.NullPointerException 01-23 10:07:59.358:E/AndroidRuntime28335:at com.ambilobes.cust\u grid.main活动$ImageLoaderTask.onPostExecuteMainActivity.java:145无人知道！！！！！！！！！！！！！！！！！！！！！！！！！你能在你的代码中显示空指针的确切位置吗？com.ambilobes.cust_grid.MainActivity$ImageLoaderTask.onPostExecuteMainActivity.java:145你能告诉我该怎么做吗？你的代码很好地工作了…谢谢。。。事实上，我不知道如何在堆栈中提升你。告诉我你应该点击我答案旁边的复选标记使它变成绿色。这将向人们表明你接受答案，这将使人们在未来更愿意提供帮助。这里有完整的说明：那么你还是有同样的问题吗？？？向我显示您获取错误的行？图像未显示在GridView中，但应用程序正在崩溃？如果它崩溃了，告诉我lineNow我的应用程序没有崩溃。。图像未显示！！要显示图像，请使用通用图像加载器类。在使用我的代码后，应用程序没有崩溃？