如何在后执行方法中更新我的 ImageAdapter

Question

我有一个由本地图像填充的 GridView 的 ImageAdapter 类。我想通过电影数据库 api 更新它。 这是我的 ImageAdapter 类 -

package jindal5.mayank.popular_movies_14ce10032_gsc;

import android.content.Context;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.GridView;
import android.widget.ImageView;

public class ImageAdapter extends BaseAdapter {
    private Context mContext;

    public ImageAdapter(Context c) {
        mContext = c;
    }

    public int getCount() {
        return mThumbIds.length;
    }

    public Object getItem(int position) {
        return null;
    }

    public long getItemId(int position) {
        return 0;
    }

    // create a new ImageView for each item referenced by the Adapter
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {
            // if it's not recycled, initialize some attributes
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(8, 8, 8, 8);
        } else {
            imageView = (ImageView) convertView;
        }

        imageView.setImageResource(mThumbIds[position]);
        return imageView;
    }

    // references to our images
    private Integer[] mThumbIds = {
            R.drawable.sample_2, R.drawable.sample_3,
            R.drawable.sample_4, R.drawable.sample_5,
            R.drawable.sample_6, R.drawable.sample_7,
            R.drawable.sample_0, R.drawable.sample_1,
            R.drawable.sample_2, R.drawable.sample_3,
            R.drawable.sample_4, R.drawable.sample_5,
            R.drawable.sample_6, R.drawable.sample_7,
            R.drawable.sample_0, R.drawable.sample_1,
            R.drawable.sample_2, R.drawable.sample_3,
            R.drawable.sample_4, R.drawable.sample_5,
            R.drawable.sample_6, R.drawable.sample_7
    };
}

这是我的 MainActivityFragment 包含 AscyncTask -

package jindal5.mayank.popular_movies_14ce10032_gsc;

import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
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.widget.ImageView;

import com.squareup.picasso.Picasso;

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;

/**
 * A placeholder fragment containing a simple view.
 */
public class MainActivityFragment extends Fragment {
    private ImageAdapter imag_adap;

    public MainActivityFragment() {
    }
    @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.menu_fragment, 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();
        if (id == R.id.action_refresh) {
            getimage imageTask = new getimage();
            imageTask.execute("popularity.desc");
            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);
        GridView grid = (GridView) rootview.findViewById(R.id.gridView);
        imag_adap = new ImageAdapter(getActivity());
        grid.setAdapter(imag_adap);
        return rootview;
    }

    public class getimage extends AsyncTask<String, Void, String[]> {
        private final String LOG_TAG = getimage.class.getSimpleName();
        public int count;
        String[] pos_path;


        @Override
        protected String[] doInBackground(String... params) {
            HttpURLConnection urlConnection = null;
            BufferedReader reader = null;
            String movieJsonStr = null;
            try {
                final String movie_url_str = "http://api.themoviedb.org/3/discover/movie?sort_by="+ params[0] +"&api_key=8d7a48043ba1d3348181e2b6615cedc7";
                URL movie_url = new URL(movie_url_str);
                urlConnection = (HttpURLConnection) movie_url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();
                InputStream inputStream = urlConnection.getInputStream();
                StringBuffer buffer = new StringBuffer();
                if (inputStream == null) {
                    return null;
                }
                reader = new BufferedReader(new InputStreamReader(inputStream));
                String line;
                while ((line = reader.readLine()) != null) {
                    buffer.append(line + "\n");
                }
                if (buffer.length() == 0) {
                    return null;
                }
                movieJsonStr = buffer.toString();
                Log.v(LOG_TAG, "Forecast string: " + movieJsonStr);
                JSONObject movieJson = new JSONObject(movieJsonStr);
                JSONArray movieJsonarray = movieJson.getJSONArray("results");
                 count = movieJsonarray.length();
                pos_path = new String[count];
                for(int i=0;i<count;i++){
                    JSONObject sin_movie = movieJsonarray.getJSONObject(i);
                    pos_path[i] = sin_movie.getString("poster_path");
                }
            } catch (IOException | JSONException e) {
                Log.e(LOG_TAG, "Error ", e);
                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);
                    }
                }
            }
            return pos_path;
            }
        @Override
        protected void onPostExecute(String[] result) {
            Uri.Builder url_for_poster = new Uri.Builder();
            ImageView[] im_vi = new ImageView[count];
            for(int j=0;j<count;j++) {
                String pos_sin_path = pos_path[j];
               Uri.Builder url_build =  url_for_poster.scheme("http").authority("image.tmdb.org/t/p").appendPath("w92").appendPath("pos_sin_path");
                String url = url_build.toString();
                Picasso.with(getActivity()).load("http://image.tmdb.org/t/p/w185//nBNZadXqJSdt05SHLqgT0HuC5Gm.jpg").into(im_vi[j]);  **probably this shows target must be null**
                //imag_adap.getItem(j) = im_vi[j];  **after uncommenting it shows variable expexted**
            }
        }
    }
}

Answer 1

如下改变适配器，

public class ImageAdapter extends BaseAdapter {
    private String drawablePrefix;
    private Context mContext;
    private ArrayList<String> mThumbUris;

    public ImageAdapter(Context c) {
        mContext = c;
        String packName=mContext.getPackageName();
        drawablePrefix="android.resource://" +packName+ "/";

        ArrayList<String> uriPaths=new ArrayList<>();// place your drawables.

        uriPaths.add(drawablePrefix+ R.drawable.weather);
        uriPaths.add(drawablePrefix+ R.drawable.wall_bird);
        uriPaths.add(drawablePrefix+ R.drawable.weather);
        uriPaths.add(drawablePrefix+ R.drawable.weather);
        uriPaths.add(drawablePrefix+ R.drawable.weather);
        uriPaths.add(drawablePrefix+ R.drawable.weather);
        uriPaths.add(drawablePrefix+ R.drawable.weather);
        mThumbUris=uriPaths;
    }

    public int getCount() {
        return mThumbUris.size();
    }

    public String getItem(int position) {
        return mThumbUris.get(position);
    }

    public long getItemId(int position) {
        return 0;
    }

    // create a new ImageView for each item referenced by the Adapter
    public View getView(int position, View convertView, ViewGroup parent) {
        ImageView imageView;
        if (convertView == null) {
            // if it's not recycled, initialize some attributes
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setPadding(8, 8, 8, 8);
        } else {
            imageView = (ImageView) convertView;
        }

        Uri imgUri=Uri.parse(mThumbUris.get(position));

        Picasso.with(mContext)
                .load(imgUri)
                .placeholder(R.drawable.weather)
                .centerCrop()
                .resize(400, 400)
                .into(imageView);

        return imageView;
    }

    public ArrayList<String> getUriList(){
        return mThumbUris;
    }
}

改变 onPostExecute 逻辑如下。

 protected void onPostExecute(String[] result) {
            Uri.Builder url_for_poster = new Uri.Builder();
            ArrayList<String> uriPaths = imag_adap.getUriList();
            uriPaths.clear();
            for (int j = 0; j < count; j++) {
                String pos_sin_path = pos_path[j];
                Uri.Builder url_build = url_for_poster.scheme("http").authority("image.tmdb.org/t/p").appendPath("w92").appendPath("pos_sin_path");
                String url = url_build.toString();
                uriPaths.add(url);
            }
            imag_adap.notifyDataSetChanged();
        }

然后它就可以正常工作了。