gridView 布局没有显示，我得到了黑屏

Question

我正在努力让GridLayout 每个街区都成为电影海报。我使用 themoviedb.org 来做到这一点。我认为我做的一切都是正确的，但我的应用程序中仍然没有显示任何内容，有人可以帮我处理我的代码。

我有 3 个类和 1 个 xml 文件

1) 第一个类是 MainActivity：

package com.example.admin.movies;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class MainActivity extends AppCompatActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }
}

2) 第二类是 MainFragment，它是我想要使用的片段，内部 AsyncTask 类显示从 JSON 查询中获取“poster_path”： 包 com.example.admin.movi​​es;

import android.net.Uri;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.annotation.Nullable;
import android.support.v4.app.Fragment;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.GridView;
import android.widget.Toast;

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.ArrayList;
import java.util.Arrays;

/**
 * Created by Admin on 11/7/2016.
 */

public class MainFragment extends Fragment {


    private ArrayList<String> imagesEndPointsList;

    public MainFragment(){

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

        GetImagesAsyncTask sync = new GetImagesAsyncTask();
        sync.execute();

        setHasOptionsMenu(true);
    }

    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
        View rootView = inflater.inflate(R.layout.activity_main,container,false);

        GridView gridView = (GridView)rootView.findViewById(R.id.grid_movies);
        gridView.setAdapter(new ImageAdapter(getContext(),imagesEndPointsList));

        gridView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
            @Override
            public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
                Toast.makeText(getContext(),""+position,Toast.LENGTH_SHORT).show();
            }
        });

        return rootView;
    }

    @Override
    public void onActivityCreated(@Nullable Bundle savedInstanceState) {
        super.onActivityCreated(savedInstanceState);
    }

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

        private String [] imagesEndPoints;
        final private String LOG_TAG = GetImagesAsyncTask.class.getSimpleName();
        //My API Key to https://www.themoviedb.org/
        String myKey;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();

            myKey = "29a99f9dc266ab3a2108e9f9511a05ed";
        }

        @Override
        protected String[] doInBackground(Void... params) {
            // These two need to be declared outside the try/catch
            // so that they can be closed in the finally block.
            HttpURLConnection urlConnection = null;
            BufferedReader reader = null;

            // Will contain the raw JSON response as a string.
            String forecastJsonStr = null;
            String API_KEY = "api_key";

            try{
                final String BASE_URL =
                        "http://api.themoviedb.org/3/movie/popular?";

                Uri buildUri = Uri.parse(BASE_URL).buildUpon()
                        .appendQueryParameter(API_KEY,myKey).build();

                URL url = new URL(buildUri.toString());

                urlConnection = (HttpURLConnection) url.openConnection();
                urlConnection.setRequestMethod("GET");
                urlConnection.connect();

                // Read the input stream into a String
                InputStream inputStream = urlConnection.getInputStream();
                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;
                }
                forecastJsonStr = buffer.toString();
                Log.v(LOG_TAG,forecastJsonStr);
                return getMovieDataFromJson(forecastJsonStr);
            }catch (IOException e) {
                Log.e(LOG_TAG, "Error ", e);
                // If the code didn't successfully get the weather data, there's no point in attempting
                // to parse it.
            } catch (JSONException e) {
                Log.e(LOG_TAG, e.getMessage(), e);
                e.printStackTrace();
            } 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 null;
        }

        @Override
        protected void onPostExecute(String[] string) {
            super.onPostExecute(string);
            if(string != null) {
                imagesEndPointsList.clear();
                for (String dayForecastStr : string) {
                    imagesEndPointsList.add(dayForecastStr);
                }
            }

        }

        private String[] getMovieDataFromJson(String JsonString) throws JSONException{

            // Weather information.  Each day's forecast info is an element of the "list" array.
            final String OWM_RESULT = "results";

            final String OWM_PATH = "poster_path";

            try{
                JSONObject forecastJson = new JSONObject(JsonString);
                JSONArray imagesArray = forecastJson.getJSONArray(OWM_RESULT);

                imagesEndPoints = new String[imagesArray.length()];

                for (int i = 0 ; i<imagesArray.length(); i++){

                    JSONObject dayForecast = imagesArray.getJSONObject(i);

                    imagesEndPoints[i] = dayForecast.getString(OWM_PATH);
                    return imagesEndPoints;
                }
            }catch (JSONException e) {
                Log.e(LOG_TAG, e.getMessage(), e);
                e.printStackTrace();
            }
            return null;
        }
    }
}

3) 我构建的适配器：

package com.example.admin.movies;

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

import com.squareup.picasso.Picasso;

import java.util.ArrayList;

/**
 * Created by Admin on 11/7/2016.
 */

public class ImageAdapter extends BaseAdapter {

    final private String BASE_URL =
            "http://image.tmdb.org/t/p/w185/";
    Context mContext;

    private ArrayList<String> endPoints;

    public ImageAdapter(Context context, ArrayList<String> arrayList){
        mContext = context;
        endPoints = arrayList;
    }

    @Override
    public int getCount() {
        return endPoints.size();
    }

    @Override
    public Object getItem(int position)
    {
        return endPoints.get(position);
    }

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

    @Override
    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;
        }

        Log.v("BASEURL",BASE_URL+endPoints.get(position));
        Picasso.with(mContext).load(BASE_URL+endPoints.get(position)).into(imageView);
        return imageView;
    }
}

4) 以及xml布局文件：

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout  xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.admin.movies.MainFragment">

<GridView xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/grid_movies"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:numColumns="auto_fit"
    android:columnWidth="90dp"
    android:verticalSpacing="10dp"
    android:horizontalSpacing="10dp"
    android:stretchMode="columnWidth"
    android:gravity="center" />

</FrameLayout>

Answer 1

我认为您的问题取决于适配器的 getView()，只需创建一个带有 imageView 的 xml 并将此资源用作每一行的项目，而不是以编程方式创建您的 imageView。

@Override

public View getView(int position, View convertView, ViewGroup parent) {

ViewHolderItem viewHolder;

if(convertView==null){

    // inflate the layout
    LayoutInflater inflater = ((Activity) mContext).getLayoutInflater();
    convertView = inflater.inflate(layoutResourceId, parent, false);

    // well set up the ViewHolder
    viewHolder = new ViewHolderItem();
    viewHolder.imageViewItem= (ImageView) convertView.findViewById(R.id.imageView);

    // store the holder with the view.
    convertView.setTag(viewHolder);

    }else{
        viewHolder = (ViewHolderItem) convertView.getTag();
    }

    // object item based on the position
    String url = BASE_URL+endPoints.get(position);

    // assign values if the object is not null
    if(url!= null) {
          Piccaso. ---.into(imageViewItem);     
    }

return convertView;

}

Answer 2

tools:context="com.example.admin.movies.MainFragment" 不会告诉 Android 替换 FrameLayout。它只是让 Android Studio 用片段呈现预览。

如果你想通过XML添加片段，你需要这样做：

<fragment class="com.example.admin.movies.MainFragment"
    android:layout_weight="1"
    android:layout_width="match_parent"
    android:layout_height="match_parent" >
</fragment>

Answer 3

您确定 AsyncTask 在您设置适配器之前完成吗？

你需要：

1. 在 OnCreateView 中启动 AsyncTask
2. 在您拥有列表后将适配器设置为您的 GridViewIn onPostExecute
3. 检查列表是否为空