GridView 适配器未填充？没有按时填充？没有在 onPostExecute() 中更新？

Question

我正在构建一个由 GridView 和从 API 提取的图像组成的 UI，我正在使用 ImageListAdapter 和 MovieFragment，当我启动应用程序时，我只是得到一个空屏幕。 我尝试过使用预下载图像列表，它可以工作。 从 API 获取数据是在 AsyncTask 上的，我认为问题出在时间上，事实上 gridview.setAdapter() 被调用得太早了。 这是代码：

public class MainActivity extends AppCompatActivity {

private final String LOG_TAG = MainActivity.class.getSimpleName();


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    if (savedInstanceState == null) {
        getFragmentManager()
                .beginTransaction()
                .add(R.id.container, new MovieFragment())
                .commit();
    }
}}

公共类 MovieFragment 扩展片段 {

private final String LOG_TAG = MovieFragment.class.getSimpleName();
public ImageListAdapter imageAdapter;
String urlPopular = "https://api.themoviedb.org/3/movie/popular?api_key=";
String urlRatings = "https://api.themoviedb.org/3/movie/top_rated?api_key=";

public MovieFragment() {
};


@Override
public void onStart() {
    super.onStart();
    FetchMovieData movieTask = new FetchMovieData();
    movieTask.execute(urlPopular);
}

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {

    View rootView = inflater.inflate(R.layout.movie_fragment_main, container, false);
    GridView gridview = (GridView) rootView.findViewById(R.id.grid_view);
    Log.d(LOG_TAG, imageAdapter.getCount() +"");
    gridview.setAdapter(imageAdapter);

    gridview.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View v,
                                int position, long id) {
            Toast.makeText(getActivity(), "" + position,
                    Toast.LENGTH_SHORT).show();
        }
    });


    return rootView;
}


public class ImageListAdapter extends ArrayAdapter {
    private Context context;
    private LayoutInflater inflater;

    private String[] imageUrls;

    public ImageListAdapter(Context context, String[] imageUrls) {
        super(context, R.layout.image_item, imageUrls);

        this.context = context;
        this.imageUrls = imageUrls;
        inflater = LayoutInflater.from(context);
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        Log.d(LOG_TAG, imageUrls[position]);
        if (null == convertView) {
            convertView = inflater.inflate(R.layout.image_item, parent, false);
        }

        Picasso
                .with(context)
                .load(imageUrls[position])
                .fit() // will explain later
                .into((ImageView) convertView);

        return convertView;
    }
}


public class FetchMovieData extends AsyncTask<String,Void,String[][]> {

    private final String LOG_TAG = FetchMovieData.class.getSimpleName();
    @Override
    protected String[][] doInBackground(String... params) {
        String url = params[0];
        if (params.length == 0){
            return null;
        }
        // Will contain the raw JSON response as a string.
        String movieJSON = null;

        try {
            movieJSON = getMovieInfo(url);
        } catch (final IOException e) {
            Log.d(LOG_TAG, "Error closing stream", e);
        }

        try{
            return getMovieDataFromJSON(movieJSON);
        }
        catch (JSONException e){
            Log.d(LOG_TAG, e.getMessage(),e);
            e.printStackTrace();
        }

        //Just in case...
        return null;
    }
    private String getMovieInfo(String myurl) throws IOException{
        HttpURLConnection urlConnection = null;
        InputStream inputStream = null;

        try{
            URL url = new URL(myurl);
            urlConnection = (HttpURLConnection) url.openConnection();
            urlConnection.setRequestMethod("GET");
            urlConnection.connect();

            inputStream = urlConnection.getInputStream();
            StringBuffer stringBuffer = new StringBuffer();
            if (inputStream == null){
                return null;
            }

            BufferedReader 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.
                stringBuffer.append(line + "\n");
            }

            if (stringBuffer.length() == 0) {
                // Stream was empty.  No point in parsing.
                return null;
            }
            Log.d(LOG_TAG, stringBuffer.toString());
            return stringBuffer.toString();
        }
        finally {
            if(urlConnection != null){
                urlConnection.disconnect();
            }
        }
    }

    private String[][] getMovieDataFromJSON(String jsonObj) throws JSONException{

        JSONObject mainJSON = new JSONObject(jsonObj);

        final String POSTERS = "poster_path";
        final String ORIGINAL_TITLE = "original_title";
        final String SYNOPSIS = "overview";
        final String USER_RATING = "vote_average";
        final String RELEASE_DATE = "release_date";
        final String RESULTS = "results";

        // Building a String[][] of movie info while:
        // movie[][0] = Poster path
        // movie[][1] = Original Title
        // movie[][2] = Synopsis
        // movie[][3] = User Rating
        // movie[][4] = Release Date

        JSONArray movieIndexArray = mainJSON.getJSONArray(RESULTS);
        String[][] movie = new String[20][5];

        for(int i = 0; i < movieIndexArray.length(); i++) {
            JSONObject movieObject = movieIndexArray.getJSONObject(i);
            movie[i][0] = movieObject.getString(POSTERS);
            movie[i][1] = movieObject.getString(ORIGINAL_TITLE);
            movie[i][2] = movieObject.getString(SYNOPSIS);
            movie[i][3] = movieObject.getString(USER_RATING);
            movie[i][4] = movieObject.getString(RELEASE_DATE);
        }

        return movie;
    }

    private String[] buildPosterArray(String[][] result){

        String[] url = new String[20];
        Uri.Builder builtUri = new Uri.Builder();
        builtUri.scheme("http");
        builtUri.authority("image.tmdb.org");
        builtUri.appendPath("t");
        builtUri.appendPath("p");
        builtUri.appendPath("w185");

        for (int i = 0 ; i < result.length ; i++){
            builtUri.appendEncodedPath((result[i][0]));
            builtUri.build();
            url[i] = builtUri.toString();
        }
        return url;

    }
    protected void onPostExecute(String[][] result){
        if(result != null){
            String[] posterArray = buildPosterArray(result);
            imageAdapter = new ImageListAdapter(getActivity(), posterArray);
            Log.d(LOG_TAG, imageAdapter.getCount() +"");
        }
    }


}

}

Answer 1

终于解决了，我用BaseAdapter的扩展代替了ArrayAdapter：

public class ImageAdapter extends BaseAdapter {
    private Context mContext;
    private String[] moviePath;

    public ImageAdapter(Context c, String[] path) {

        mContext = c;
        this.moviePath = path;
    }

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

    //Needed due to methods being abstract
    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 = (ImageView) convertView;
        if (imageView == null) {
            // if it's not recycled, initialize some attributes
            imageView = new ImageView(mContext);
            imageView.setLayoutParams(new GridView.LayoutParams(500, 500));
            imageView.setPadding(5, 5, 5, 5);
        } else {
            imageView = (ImageView) convertView;
        }

        //imageView.setImageResource(mThumbIds[position]);
        Picasso.with(getActivity())
                .load(moviePath[position])
                .fit()
                .into(imageView);
        return imageView;
    }
}

我还在 onPostExecute() 方法中使用了 setAdapter()。

谢谢大家的帮助=D