我一直在努力解决这个问题，当我点击我的应用程序中的刷新按钮时，图像不会加载到屏幕上。
这是DataFragment文件，当我构建这个应用程序时没有错误。
package com.example.popularmovis;
import android.app.Fragment;
import android.content.SharedPreferences;
import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.preference.PreferenceManager;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.GridView;
import android.os.AsyncTask;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.jar.JarException;
/**
* A placeholder fragment containing a simple view.
*/
public class DataFragment extends Fragment {
public ImageAdapter display;
public DataFragment() {
}
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
// Add this line in order for this fragment to handle menu events.
setHasOptionsMenu(true);
}
@Override
public void onCreateOptionsMenu(Menu menu, MenuInflater inflater) {
inflater.inflate(R.menu.datafragment_menu, menu);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_refresh) {
FetchMovieData movieData = new FetchMovieData();
movieData.execute();
return true;
}
return super.onOptionsItemSelected(item);
}
@Override
public View onCreateView (LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container, false);
display = new ImageAdapter(rootView.getContext());
GridView gridView = (GridView) rootView.findViewById(R.id.gridView_movies);
gridView.setAdapter(display); // uses the view to get the context instead of getActivity().
return rootView;
}
public class FetchMovieData extends AsyncTask<Void, Void, String[]>{
private final String LOG_TAG = FetchMovieData.class.getSimpleName();
private String[] extractdisplayFromJason(String jasnData)
throws JSONException{
//These jason display need to be extracted
final String movie_results = "results";
final String movie_poster = "poster_path";
JSONObject movieData = new JSONObject(jasnData);
JSONArray movieArray = movieData.getJSONArray(movie_results);
String[] posterAddreess = new String[movieArray.length()];
//Fill ther posterAddreess with the URL to display
for(int j=0; j < movieArray.length(); j++){
String posterPath;
JSONObject movieArrayItem = movieArray.getJSONObject(j);
posterPath = movieArrayItem.getString(movie_poster);
posterAddreess[j] = "http://image.tmdb.org/t/p/w185/" + posterPath;
}
for (String s : posterAddreess) {
Log.v(LOG_TAG, "Thumbnail Links: " + s);
}
return posterAddreess;
}
@Override
protected String[] doInBackground(Void... params) {
HttpURLConnection urlConnection = null;
BufferedReader reader = null;
String JsonData = null;
String country = "US";
String rating = "R";
String sort = "popularity.desc";
String apiKey = "";
//building the URL for the movie DB
try {
//building the URL for the movie DB
final String MovieDatabaseUrl = "https://api.themoviedb.org/3/discover/movie?";
final String Country_for_release = "certification_country";
final String Rating = "certification";
final String Sorting_Order = "sort_by";
final String Api_Id = "api_key";
Uri buildUri = Uri.parse(MovieDatabaseUrl).buildUpon()
.appendQueryParameter(Country_for_release, country)
.appendQueryParameter(Rating, rating)
.appendQueryParameter(Sorting_Order, sort)
.appendQueryParameter(Api_Id, apiKey)
.build();
//Converting URI to URL
URL url = new URL(buildUri.toString());
Log.v(LOG_TAG, "Built URI = "+ buildUri.toString());
//Create the request to the Movie Database
urlConnection = (HttpURLConnection) url.openConnection();
urlConnection.setRequestMethod("GET");
urlConnection.connect();
//Read the input from the database into string
InputStream inputStream = urlConnection.getInputStream();
//StringBuffer for string Manipulation
StringBuffer buffer = new StringBuffer();
if (inputStream == null) {
// Nothing to do.
return null;
}
reader = new BufferedReader(new InputStreamReader(inputStream));
String line;
while ((line = reader.readLine()) != null) {
// Since it's JSON, adding a newline isn't necessary (it won't affect parsing)
// But it does make debugging a *lot* easier if you print out the completed
// buffer for debugging.
buffer.append(line + "\n");
}
if (buffer.length() == 0) {
// Stream was empty. No point in parsing.
return null;
}
JsonData = buffer.toString();
Log.v(LOG_TAG,"Forecaast Jason String" + JsonData );
} catch (IOException e) {
// If the code didn't successfully get the weather data, there's no point in attemping
// to parse it.
return null;
} finally {
if (urlConnection != null) {
urlConnection.disconnect();
}
if (reader != null) {
try {
reader.close();
} catch (final IOException e) {
Log.e(LOG_TAG, "Error closing stream", e);
}
}
try {
return extractdisplayFromJason(JsonData);
} catch (JSONException e) {
Log.e(LOG_TAG, e.getMessage(), e);
e.printStackTrace();
}
}
return null;
}
protected void onPostExecute(String[] posterAddreess) {
for (String poster : posterAddreess) {
display.addItem(poster);
}
}
}
}
这是ImageAdapter代码
package com.example.popularmovis;
import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import com.example.popularmovis.R;
import com.squareup.picasso.Picasso;
import java.util.ArrayList;
public class ImageAdapter extends BaseAdapter {
private Context mContext;
public ArrayList<String> images = new ArrayList<String>();
public ImageAdapter(Context c){
mContext = c;
}
@Override
public int getCount(){
return images.size();
}
@Override
public Object getItem(int position){
return images.get(position);
}
public long getItemId(int position){
return 0;
}
public View getView(int position, View convertView, ViewGroup parent){
ImageView imageview;
if (convertView == null){
imageview = new ImageView(mContext);
imageview.setPadding(0, 0, 0, 0);
//imageview.setLayoutParams(new GridLayout.MarginLayoutParams(ViewGroup.LayoutParams.FILL_PARENT, ViewGroup.LayoutParams.WRAP_CONTENT));
imageview.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
imageview.setAdjustViewBounds(true);
} else {
imageview = (ImageView) convertView;
}
Picasso.with(mContext).load(images.get(position)).placeholder(R.mipmap.ic_launcher).into(imageview);
return imageview;
}
/*
Custom methods
*/
public void addItem(String url){
images.add(url);
}
public void clearItems() {
images.clear();
}
}
答案 0 :(得分：2)
在这样的onCreate方法中使用它时，意味着该对象是方法的本地对象，不能在其他方法中使用。
ImageAdapter display = new ImageAdapter(rootView.getContext());
首先创建一个全局类成员变量
private ImageAdapter display;
然后在你的onCreate方法中执行此操作
display = new ImageAdapter(rootView.getContext());