6月10日，配置 RecyclerView 以显示图片，Android 开发，每日20行，第93天。

FlickrFetchr.java

package com.example.aster.photogallery;

import android.net.Uri;
import android.util.Log;

import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;

import java.io.ByteArrayOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.ArrayList;
import java.util.List;

public class FlickrFetchr {

    private static final String TAG = "FlickrFetchr";

    private static final String API_KEY = "4f721bgafa75bf6d2cb9af54f937bb70";

    public byte[] getUrlBytes(String urlSpec) throws IOException {
        URL url = new URL(urlSpec);
        HttpURLConnection connection = (HttpURLConnection) url.openConnection();

        try {
            ByteArrayOutputStream out = new ByteArrayOutputStream();
            InputStream in = connection.getInputStream();

            if (connection.getResponseCode() != HttpURLConnection.HTTP_OK) {
                throw new IOException(connection.getResponseMessage() +
                        ": with " +
                        urlSpec);
            }

            int bytesRead = 0;
            byte[] buffer = new byte[1024];
            while ((bytesRead = in.read(buffer)) > 0) {
                out.write(buffer, 0, bytesRead);
            }
            out.close();
            return out.toByteArray();
        } finally {
            connection.disconnect();
        }
    }

    public String getUrlString(String urlSpec) throws IOException {
        return new String(getUrlBytes(urlSpec));
    }

    public List<GalleryItem> fetchItems() {

        List<GalleryItem> items = new ArrayList<>();

        try {
            String url = Uri.parse("https://api.flickr.com/services/rest/")
                    .buildUpon()
                    .appendQueryParameter("method", "flickr.photos.getRecent")
                    .appendQueryParameter("api_key", API_KEY)
                    .appendQueryParameter("format", "json")
                    .appendQueryParameter("nojsoncallback", "1")
                    .appendQueryParameter("extras", "url_s")
                    .build().toString();
            String jsonString = getUrlString(url);
            Log.i(TAG, "Received JSON: " + jsonString);
            JSONObject jsonBody = new JSONObject(jsonString);
            parseItems(items, jsonBody);
        } catch (IOException ioe) {
            Log.e(TAG, "Failed to fetch items", ioe);
        } catch (JSONException je) {
            Log.e(TAG, "Failed to parse JSON", je);
        }

        return items;
    }

    private void parseItems(List<GalleryItem> items, JSONObject jsonBody)
        throws IOException, JSONException {

        JSONObject photosJsonObject = jsonBody.getJSONObject("photos");
        JSONArray photoJsonArray = photosJsonObject.getJSONArray("photo");

        for (int i = 0; i < photoJsonArray.length(); i++) {
            JSONObject photoJsonObject = photoJsonArray.getJSONObject(i);

            GalleryItem item = new GalleryItem();
            item.setId(photoJsonObject.getString("id"));
            item.setCaption(photoJsonObject.getString("title"));

            if (!photoJsonObject.has("url_s")) {
                continue;
            }

            item.setUrl(photoJsonObject.getString("url_s"));
            items.add(item);
        }
    }
}

GalleryItem.java

package com.example.aster.photogallery;

public class GalleryItem {
    private String mCaption;
    private String mId;
    private String mUrl;

    @Override
    public String toString() {
        return mCaption;
    }

    public String getCaption() {
        return mCaption;
    }

    public void setCaption(String caption) {
        mCaption = caption;
    }

    public String getId() {
        return mId;
    }

    public void setId(String id) {
        mId = id;
    }

    public String getUrl() {
        return mUrl;
    }

    public void setUrl(String url) {
        mUrl = url;
    }
}

PhotoGalleryActivity.java

package com.example.aster.photogallery;

import android.support.v4.app.Fragment;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;

public class PhotoGalleryActivity extends SingleFragmentActivity {

    @Override
    protected Fragment createFragment() {
        return PhotoGalleryFragment.newInstance();
    }
}

PhotoGalleryFragment.java

package com.example.aster.photogallery;

import android.graphics.drawable.Drawable;
import android.os.AsyncTask;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.TextView;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

public class PhotoGalleryFragment extends Fragment {

    private static final String TAG = "PhotoGalleryFragment";

    private RecyclerView mPhotoRecyclerView;
    private List<GalleryItem> mItems = new ArrayList<>();

    public static PhotoGalleryFragment newInstance() {
        return new PhotoGalleryFragment();
    }

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setRetainInstance(true);
        new FetchItemsTask().execute();
    }

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

        mPhotoRecyclerView = (RecyclerView) v.findViewById(R.id.photo_recycler_view);
        mPhotoRecyclerView.setLayoutManager(new GridLayoutManager(getActivity(), 3));

        setupAdapter();

        return v;
    }

    private void setupAdapter() {
        if (isAdded()) {
            mPhotoRecyclerView.setAdapter(new PhotoAdapter(mItems));
        }
    }

    private class PhotoHolder extends RecyclerView.ViewHolder {
        private ImageView mItemImageView;

        public PhotoHolder(View itemView) {
            super(itemView);

            mItemImageView = (ImageView) itemView.findViewById(R.id.item_image_view);
        }

        public void bindDrawable(Drawable drawable) {
            mItemImageView.setImageDrawable(drawable);
        }
    }

    private class PhotoAdapter extends RecyclerView.Adapter<PhotoHolder> {

        private List<GalleryItem> mGalleryItems;

        public PhotoAdapter(List<GalleryItem> galleryItems) {
            mGalleryItems = galleryItems;
        }

        @Override
        public PhotoHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
            LayoutInflater inflater = LayoutInflater.from(getActivity());
            View view = inflater.inflate(R.layout.list_item_gallery, viewGroup, false);
            return new PhotoHolder(view);
        }

        @Override
        public void onBindViewHolder(PhotoHolder photoHolder, int position) {
            GalleryItem galleryItem = mGalleryItems.get(position);
            Drawable placeholder = getResources().getDrawable(R.drawable.bill_up_close);
            photoHolder.bindDrawable(placeholder);
        }

        @Override
        public int getItemCount() {
            return mGalleryItems.size();
        }
    }

    private class FetchItemsTask extends AsyncTask<Void, Void, List<GalleryItem>> {
        @Override
        protected List<GalleryItem> doInBackground(Void... params) {
            return new FlickrFetchr().fetchItems();
        }

        @Override
        protected void onPostExecute(List<GalleryItem> items) {
            mItems = items;
            setupAdapter();
        }
    }
}

SingleFragmentActivity.java

package com.example.aster.photogallery;

import android.os.Bundle;
import android.support.annotation.LayoutRes;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v7.app.AppCompatActivity;

public abstract class SingleFragmentActivity extends AppCompatActivity {

    protected abstract Fragment createFragment();

    @LayoutRes
    protected int getLayoutResId() {
        return R.layout.activity_fragment;
    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(getLayoutResId());

        FragmentManager fm = getSupportFragmentManager();
        Fragment fragment = fm.findFragmentById(R.id.fragment_container);

        if (fragment == null) {
            fragment = createFragment();
            fm.beginTransaction().add(R.id.fragment_container, fragment).commit();
        }
    }
}

AndroidManifest.java

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.aster.photogallery">

    <uses-permission android:name="android.permission.INTERNET" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <activity android:name=".PhotoGalleryActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

activity_fragment.xml

<?xml version="1.0" encoding="utf-8"?>
<FrameLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/fragment_container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"/>

fragment_photo_gallery.xml

<?xml version="1.0" encoding="utf-8"?>
<android.support.v7.widget.RecyclerView
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/photo_recycler_view"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context="com.example.aster.photogallery.PhotoGalleryActivity" />

list_item_gallery.xml

<?xml version="1.0" encoding="utf-8"?>
<ImageView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/item_image_view"
    android:layout_width="match_parent"
    android:layout_height="120dp"
    android:layout_gravity="center"
    android:scaleType="centerCrop">
</ImageView>