如何在未加载图像时通过使用 volley 解析 json 数据在列表视图中显示背景图像

Question

如何在未加载图像时通过使用 volley 解析 json 数据在列表视图中显示背景图像。或者如果图像 url 不存在于 json 中，则默认情况下应显示背景图像。

在您可以在列表中看到的图像中 ist image url 不存在于 json 中，因此 ist 图像显示为空白图像。

虽然它应该显示为默认图像。

我必须用一张图片替换空白图片。我想在图像未加载时放置一个背景图像，它应该显示为所有图像的默认值。下载图像后，应将图像替换为默认图像
我用过 Volley Library 。 如何在未加载图像且不存在图像 url 时设置背景图像，默认情况下它应该作为背景图像出现？

主要活动

public class MainActivity extends Activity {
    // Log tag
    private static final String TAG = MainActivity.class.getSimpleName();
    private static final String url = "http://lztsyhmtyk.localtunnel.me/api/v1/restaurants?per_page=10&page=1&sort_col=average_ratings";
    // Movies json url
    //private static final String url = "http://api.androidhive.info/json/movies.json";
    private ProgressDialog pDialog;
    private List<Movie> movieList = new ArrayList<Movie>();
    private ListView listView;
    private CustomListAdapter adapter;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        listView = (ListView) findViewById(R.id.list);
        adapter = new CustomListAdapter(this, movieList);
        listView.setAdapter(adapter);
        pDialog = new ProgressDialog(this);
        // Showing progress dialog before making http request
        pDialog.setMessage("Loading...");
        pDialog.show();
        // changing action bar color
        getActionBar().setBackgroundDrawable(
                new ColorDrawable(Color.parseColor("#1b1b1b")));
        // Creating volley request obj
        JsonArrayRequest movieReq = new JsonArrayRequest(url,
                new Response.Listener<JSONArray>() {
                    @Override
                    public void onResponse(JSONArray response) {
                        Log.d(TAG, response.toString());
                        hidePDialog();
                        // Parsing json
                        for (int i = 0; i < response.length(); i++) {
                            try {
                                JSONObject obj = response.getJSONObject(i);
                                Movie movie = new Movie();
                                //movie.setTitle(obj.getString("title"));
                                movie.setName(obj.getString("name"));
                                //movie.setThumbnailUrl(obj.getString("image"));
                                movie.setThumbnailUrl(obj.getString("image_url"));
                                movie.setAverage_ratings(obj.getString("average_ratings"));
                                movie.setCuisine(obj.getString("cuisine"));
                                movie.setAddress(obj.getJSONObject("address").getString("area"));
                                //movie.setAddress(obj.getString("address"));
                                //movie.setYear(obj.getInt("releaseYear"));
                                // Genre is json array
                                /*JSONArray genreArry = obj.getJSONArray("genre");
                                ArrayList<String> genre = new ArrayList<String>();
                                for (int j = 0; j < genreArry.length(); j++) {
                                    genre.add((String) genreArry.get(j));
                                }
                                movie.setGenre(genre);*/
                                // adding movie to movies array
                                movieList.add(movie);
                            } catch (JSONException e) {
                                e.printStackTrace();
                            }
                        }

                        // notifying list adapter about data changes
                        // so that it renders the list view with updated data
                        adapter.notifyDataSetChanged();
                    }
                }, new Response.ErrorListener() {
                    @Override
                    public void onErrorResponse(VolleyError error) {
                        VolleyLog.d(TAG, "Error: " + error.getMessage());
                        hidePDialog();

                    }
                });

        // Adding request to request queue
        AppController.getInstance().addToRequestQueue(movieReq);
    }

    @Override
    public void onDestroy() {
        super.onDestroy();
        hidePDialog();
    }

    private void hidePDialog() {
        if (pDialog != null) {
            pDialog.dismiss();
            pDialog = null;
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

}

listrow.xml

 <?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:background="@drawable/list_row_selector"
        android:padding="8dp" >

        <!-- Thumbnail Image -->
        <com.android.volley.toolbox.NetworkImageView
            android:id="@+id/thumbnail"
            android:layout_width="120dp"
            android:layout_height="80dp"
            android:layout_alignParentLeft="true"
            android:layout_marginRight="8dp" />
        <ImageView
            android:id="@+id/img"
            android:layout_width="120dp"
            android:layout_height="80dp"
            android:layout_alignParentLeft="true"
            android:layout_marginRight="8dp"
            android:src="@drawable/bc"
            />
        <!-- Restaurant name  -->
        <TextView
            android:id="@+id/name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:layout_toRightOf="@+id/thumbnail"
            android:textSize="@dimen/title"
            android:textStyle="bold" />

        <TextView
            android:id="@+id/area"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/name"

            android:layout_toRightOf="@+id/thumbnail"
            android:textSize="@dimen/rating" />

        <!-- Rating -->
        <TextView
            android:id="@+id/average_ratings"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/area"
            android:layout_toRightOf="@+id/thumbnail"

            android:textSize="@dimen/rating" />

        <TextView
            android:id="@+id/cuisine"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/average_ratings"

            android:layout_toRightOf="@+id/thumbnail"
            android:textSize="@dimen/rating" />

        <!-- Genre -->
       <!-- <TextView
            android:id="@+id/genre"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/rating"
            android:layout_marginTop="5dp"
            android:layout_toRightOf="@+id/thumbnail"
            android:textColor="@color/genre"
            android:textSize="@dimen/genre" />-->
    <!--
        &lt;!&ndash; Release Year &ndash;&gt;
        <TextView
            android:id="@+id/releaseYear"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_alignParentRight="true"
            android:textColor="@color/year"
            android:textSize="@dimen/year" />-->

    </RelativeLayout>

电影.java

public class Movie {
    private String name, thumbnailUrl;
    //private int year;
    private String average_ratings,area,cuisine,address;
//  private ArrayList<String> genre;

    public Movie() {
    }

    public Movie(String name, String thumbnailUrl, String average_ratings,String area,String cuisine,String address
            ) {
        this.name = name;
        this.thumbnailUrl = thumbnailUrl;
        //this.year = year;
        this.average_ratings = average_ratings;
        this.area=area;
        this.cuisine=cuisine;
this.address=address;
        //this.genre = genre;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getThumbnailUrl() {
        return thumbnailUrl;
    }

    public void setThumbnailUrl(String thumbnailUrl) {
        this.thumbnailUrl = thumbnailUrl;
    }

    /*public int getYear() {
        return year;
    }*/

    /*public void setYear(int year) {
        this.year = year;
    }*/

    public String getAverage_ratings() {
        return average_ratings;
    }

    public void setAverage_ratings(String average_ratings) {
        this.average_ratings = average_ratings;
    }
    public String getAddress() {
        return address;
    }

    public void setAddress(String address) {
        this.address = address;
    }

    public String getCuisine() {
        return cuisine;
    }

    public void setCuisine(String cuisine) {
        this.cuisine = cuisine;
    }
    /*public ArrayList<String> getGenre() {
        return genre;
    }

    public void setGenre(ArrayList<String> genre) {
        this.genre = genre;
    }
*/
}

customlistadapter.java

 public class CustomListAdapter extends BaseAdapter {
        private Activity activity;
        private LayoutInflater inflater;
        private List<Movie> movieItems;
        ImageLoader imageLoader = AppController.getInstance().getImageLoader();

        public CustomListAdapter(Activity activity, List<Movie> movieItems) {
            this.activity = activity;
            this.movieItems = movieItems;
        }

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

        @Override
        public Object getItem(int location) {
            return movieItems.get(location);
        }

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

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

            if (inflater == null)
                inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
            if (convertView == null)
                convertView = inflater.inflate(R.layout.list_row, null);

            if (imageLoader == null)
                imageLoader = AppController.getInstance().getImageLoader();
            /*ImageView img;
            img = (ImageView)convertView
                    .findViewById(R.id.img);

            img.setImageResource(R.drawable.bc);
            else {*/
            NetworkImageView thumbNail = (NetworkImageView) convertView
                    .findViewById(R.id.thumbnail);
            TextView name = (TextView) convertView.findViewById(R.id.name);
            TextView average_ratings = (TextView) convertView.findViewById(R.id.average_ratings);
            TextView address=(TextView) convertView.findViewById(R.id.area);
            TextView cuisine =(TextView) convertView.findViewById(R.id.cuisine);
            //TextView genre = (TextView) convertView.findViewById(R.id.genre);
            //TextView year = (TextView) convertView.findViewById(R.id.releaseYear);

            // getting movie data for the row
            Movie m = movieItems.get(position);

            // thumbnail image
            //thumbNail.setImageUrl(m.getThumbnailUrl(), imageLoader);
            //if (TextUtils.isEmpty(m.getThumbnailUrl()))
                //thumbNail.setImageResource(R.drawable.bc);



            //else
                //Log.d("KeyHash:","Neeraj");
                thumbNail.setImageUrl(m.getThumbnailUrl(), imageLoader);
            /*if (m.getThumbnailUrl().compareTo("")!=0)
                thumbNail.setImageUrl(m.getThumbnailUrl(), imageLoader);
            //else{
            //thumbNail.setImageResource(R.drawable.bc);

                else {

                    thumbNail.setDefaultImageResId(R.drawable.bc);
                    //thumbNail.setErrorImageResId(R.drawable.bc);

            }*/


            // title
            name.setText(m.getName());

            // rating
            average_ratings.setText("Rating: " + String.valueOf(m.getAverage_ratings()));
            address.setText("Area: " + String.valueOf(m.getAddress()));
            cuisine.setText("Cusine: " + String.valueOf(m.getCuisine()));
            /*// genre
            String genreStr = "";
            for (String str : m.getGenre()) {
                genreStr += str + ", ";
            }
            genreStr = genreStr.length() > 0 ? genreStr.substring(0,
                    genreStr.length() - 2) : genreStr;
            genre.setText(genreStr);

            // release year
            year.setText(String.valueOf(m.getYear()));*/

            return convertView;
        }



    }

应用控制器.java

public class AppController extends Application {

    public static final String TAG = AppController.class.getSimpleName();

    private RequestQueue mRequestQueue;
    private ImageLoader mImageLoader;

    private static AppController mInstance;

    @Override
    public void onCreate() {
        super.onCreate();
        mInstance = this;
    }

    public static synchronized AppController getInstance() {
        return mInstance;
    }

    public RequestQueue getRequestQueue() {
        if (mRequestQueue == null) {
            mRequestQueue = Volley.newRequestQueue(getApplicationContext());
        }

        return mRequestQueue;
    }

    public ImageLoader getImageLoader() {
        getRequestQueue();
        if (mImageLoader == null) {
            mImageLoader = new ImageLoader(this.mRequestQueue,
                    new LruBitmapCache());
        }
        return this.mImageLoader;
    }

    public <T> void addToRequestQueue(Request<T> req, String tag) {
        // set the default tag if tag is empty
        req.setTag(TextUtils.isEmpty(tag) ? TAG : tag);
        getRequestQueue().add(req);
    }

    public <T> void addToRequestQueue(Request<T> req) {
        req.setTag(TAG);
        getRequestQueue().add(req);
    }

    public void cancelPendingRequests(Object tag) {
        if (mRequestQueue != null) {
            mRequestQueue.cancelAll(tag);
        }
    }

Answer 1

删除另一个图像视图后将此代码放入适配器中

 // get reference of your imageloader 
   imageLoader = AppController.getInstance().getImageLoader();  

    NetworkImageView thumbNail = (NetworkImageView) convertView
                    .findViewById(R.id.thumbnail);
        thumbNail .setDefaultImageResId(R.drawable.yourdrawable);

       // getting movie data for the row
            Movie m = movieItems.get(position); 

// now it time to load image 
 thumbNail.setImageUrl(m.getThumbnailUrl(), imageLoader);

Answer 2

需要更改 CustomListAdapter 和 list_row.xml。

更新：

自定义列表适配器

public class CustomListAdapter extends BaseAdapter {
    private Activity activity;
    private LayoutInflater inflater;
    private List<Movie> movieItems;
    ImageLoader imageLoader = AppController.getInstance().getImageLoader();

    public CustomListAdapter(Activity activity, List<Movie> movieItems) {
        this.activity = activity;
        this.movieItems = movieItems;
    }

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

    @Override
    public Object getItem(int location) {
        return movieItems.get(location);
    }

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

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

        if (inflater == null)
            inflater = (LayoutInflater) activity.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        if (convertView == null)
            convertView = inflater.inflate(R.layout.list_row, null);

        if (imageLoader == null)
            imageLoader = AppController.getInstance().getImageLoader();
        /*ImageView img;
        img = (ImageView)convertView
                .findViewById(R.id.img);

        img.setImageResource(R.drawable.bc);
        else {*/

        NetworkImageView _ImageView = (NetworkImageView) convertView.findViewById(R.id.thumbnail);
         _ImageView.setDefaultImageResId(R.drawable.bc);
        //NetworkImageView.setImageUrl(m.getThumbnailUrl(), ImageLoader);
        /*NetworkImageView thumbNail = (NetworkImageView) convertView
                .findViewById(R.id.thumbnail);*/
        TextView name = (TextView) convertView.findViewById(R.id.name);
        TextView average_ratings = (TextView) convertView.findViewById(R.id.average_ratings);
        TextView address=(TextView) convertView.findViewById(R.id.area);
        TextView cuisine =(TextView) convertView.findViewById(R.id.cuisine);
        //TextView genre = (TextView) convertView.findViewById(R.id.genre);
        //TextView year = (TextView) convertView.findViewById(R.id.releaseYear);

        // getting movie data for the row
        Movie m = movieItems.get(position);

        // thumbnail image
        //_ImageView.setImageUrl(m.getThumbnailUrl(), imageLoader);
        /*if (TextUtils.isEmpty(m.getThumbnailUrl()))
            thumbNail.setImageResource(R.drawable.bc);



        else
            //Log.d("KeyHash:","Neeraj");*/
        _ImageView.setImageUrl(m.getThumbnailUrl(), imageLoader);
        /*if (m.getThumbnailUrl().compareTo("")!=0)
            thumbNail.setImageUrl(m.getThumbnailUrl(), imageLoader);
        //else{
        //thumbNail.setImageResource(R.drawable.bc);

            else {

                thumbNail.setDefaultImageResId(R.drawable.bc);
                //thumbNail.setErrorImageResId(R.drawable.bc);

        }*/


        // title
        name.setText(m.getName());

        // rating
        average_ratings.setText("Rating: " + String.valueOf(m.getAverage_ratings()));
        address.setText("Area: " + String.valueOf(m.getAddress()));
        cuisine.setText("Cusine: " + String.valueOf(m.getCuisine()));
        /*// genre
        String genreStr = "";
        for (String str : m.getGenre()) {
            genreStr += str + ", ";
        }
        genreStr = genreStr.length() > 0 ? genreStr.substring(0,
                genreStr.length() - 2) : genreStr;
        genre.setText(genreStr);

        // release year
        year.setText(String.valueOf(m.getYear()));*/

        return convertView;
    }



}

list_row.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="wrap_content"
    android:background="@drawable/list_row_selector"
    android:padding="8dp" >

    <!-- Thumbnail Image -->
    <com.android.volley.toolbox.NetworkImageView
        android:id="@+id/thumbnail"
        android:layout_width="120dp"
        android:layout_height="80dp"
        android:layout_alignParentLeft="true"
        android:layout_marginRight="8dp"

        />

    <!-- Restaurant name  -->
    <TextView
        android:id="@+id/name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"

        android:layout_toRightOf="@+id/thumbnail"
        android:textSize="@dimen/title"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/area"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/name"

        android:layout_toRightOf="@+id/thumbnail"
        android:textSize="@dimen/rating" />

    <!-- Rating -->
    <TextView
        android:id="@+id/average_ratings"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/area"
        android:layout_toRightOf="@+id/thumbnail"

        android:textSize="@dimen/rating" />

    <TextView
        android:id="@+id/cuisine"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/average_ratings"

        android:layout_toRightOf="@+id/thumbnail"
        android:textSize="@dimen/rating" />

    <!-- Genre -->
   <!-- <TextView
        android:id="@+id/genre"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:layout_below="@id/rating"
        android:layout_marginTop="5dp"
        android:layout_toRightOf="@+id/thumbnail"
        android:textColor="@color/genre"
        android:textSize="@dimen/genre" />-->
<!--
    &lt;!&ndash; Release Year &ndash;&gt;
    <TextView
        android:id="@+id/releaseYear"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentRight="true"
        android:textColor="@color/year"
        android:textSize="@dimen/year" />-->

</RelativeLayout>

更改问题解决后请参见图像。

Answer 3

删除您的 ImageView 并将 android:src="@drawable/bc" 设置为您的 NetworkImageView ：

<?xml version="1.0" encoding="utf-8"?>
    <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:background="@drawable/list_row_selector"
        android:padding="8dp" >

        <!-- Thumbnail Image -->
        <com.android.volley.toolbox.NetworkImageView
            android:id="@+id/thumbnail"
            android:layout_width="120dp"
            android:layout_height="80dp"
            android:layout_alignParentLeft="true"
            android:layout_marginRight="8dp"
            android:src="@drawable/bc" />
        <!-- Restaurant name  -->
        <TextView
            android:id="@+id/name"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"

            android:layout_toRightOf="@+id/thumbnail"
            android:textSize="@dimen/title"
            android:textStyle="bold" />

        <TextView
            android:id="@+id/area"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/name"

            android:layout_toRightOf="@+id/thumbnail"
            android:textSize="@dimen/rating" />

        <!-- Rating -->
        <TextView
            android:id="@+id/average_ratings"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/area"
            android:layout_toRightOf="@+id/thumbnail"

            android:textSize="@dimen/rating" />

        <TextView
            android:id="@+id/cuisine"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/average_ratings"

            android:layout_toRightOf="@+id/thumbnail"
            android:textSize="@dimen/rating" />

        <!-- Genre -->
       <!-- <TextView
            android:id="@+id/genre"
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_below="@id/rating"
            android:layout_marginTop="5dp"
            android:layout_toRightOf="@+id/thumbnail"
            android:textColor="@color/genre"
            android:textSize="@dimen/genre" />-->
    <!--
        &lt;!&ndash; Release Year &ndash;&gt;
        <TextView
            android:id="@+id/releaseYear"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_alignParentBottom="true"
            android:layout_alignParentRight="true"
            android:textColor="@color/year"
            android:textSize="@dimen/year" />-->

    </RelativeLayout>