android - UI 上不显示可绘制图像？

Question

我正在尝试显示一个列表，该列表旁边有一个图像和一些文本。除了主课，我还有两个类。 imageHandler 类将图片从 URL 下载到可绘制对象。 listClass 将图像设置为指定的 imageView 和 TextView 。当我包含一个 URL 时，图片根本不显示。有帮助吗？

列表类；

import android.app.Activity;
import android.graphics.drawable.Drawable;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.TextView;

public class listClass extends ArrayAdapter<String>{

    private final Activity context;
    private final String[] web;
    private final Drawable[] imageId;
    public listClass(Activity context,
                      String[] web, Drawable[] imageId) {
        super(context, R.layout.list, web);
        this.context = context;
        this.web = web;
        this.imageId = imageId;

    }
    @Override
    public View getView(int position, View view, ViewGroup parent) {
        LayoutInflater inflater = context.getLayoutInflater();
        View rowView= inflater.inflate(R.layout.list, null, true);
        TextView txtTitle = (TextView) rowView.findViewById(R.id.txt);

        ImageView imageView = (ImageView) rowView.findViewById(R.id.img);
        txtTitle.setText(web[position]);

        imageView.setImageDrawable(imageId[position]);
        return rowView;
    }
}

图像处理器类；

import android.media.Image;
import java.net.URL;
import android.graphics.BitmapFactory;
import java.io.InputStream;
import android.graphics.drawable.Drawable;

public class imageHandler {

    Image picture;


    public static Drawable LoadImageFromWebOperations(String url) {
        try {
            InputStream is = (InputStream) new URL(url).getContent();
            Drawable d = Drawable.createFromStream(is, "earthdownload");
            return d;
        } catch (Exception e) {
            return null;
        }
    }
}

主要 Activity ；

import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.view.View;
import android.support.design.widget.NavigationView;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarDrawerToggle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.app.FragmentManager;
import android.widget.FrameLayout;
import android.widget.Button;
import android.os.Bundle;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ListView;
import android.widget.Toast;
import android.app.Activity;
import android.graphics.BitmapFactory;
import android.graphics.drawable.Drawable;




public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener   {

    ListView list;
    String[] web = {
            "asd "};
    imageHandler imagess = new imageHandler();
    Drawable[] imageId = { imagess.LoadImageFromWebOperations("http://egyptianstreets.com/wp-content/uploads/2016/08/satelliteegypt-400x240.jpg")
            };

    Handler handler;
    Button button;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        TextView text = (TextView)findViewById(R.id.textView);
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.setDrawerListener(toggle);
        toggle.syncState();
        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);
        listClass adapter = new
                listClass(MainActivity.this, web, imageId);
        list=(ListView)findViewById(R.id.list);
        list.setAdapter(adapter);
        list.setOnItemClickListener(new AdapterView.OnItemClickListener() {

            @Override
            public void onItemClick(AdapterView<?> parent, View view,
                                    int position, long id) {
                Toast.makeText(MainActivity.this, "You Clicked at " +web[+ position], Toast.LENGTH_SHORT).show();
            }
        });

    }

Answer 1

我建议您在这里使用 Volley 库。它为您处理网络和缓存部分。您可以像这样创建 Volley 请求

公共(public)类 CustomVolleyRequest {

private static CustomVolleyRequest customVolleyRequest;
private static Context context;
private RequestQueue requestQueue;
private ImageLoader imageLoader;


private CustomVolleyRequest(Context context) {
    this.context = context;
    this.requestQueue = getRequestQueue();

    imageLoader = new ImageLoader(requestQueue,
            new ImageLoader.ImageCache() {
                private final LruCache<String, Bitmap>
                        cache = new LruCache<String, Bitmap>(20);

                @Override
                public Bitmap getBitmap(String url) {
                    return cache.get(url);
                }

                @Override
                public void putBitmap(String url, Bitmap bitmap) {
                    cache.put(url, bitmap);
                }
            });
}

public static synchronized CustomVolleyRequest getInstance(Context context) {
    if (customVolleyRequest == null) {
        customVolleyRequest = new CustomVolleyRequest(context);
    }
    return customVolleyRequest;
}

public RequestQueue getRequestQueue() {
    if (requestQueue == null) {
        Cache cache = new DiskBasedCache(context.getCacheDir(), 10 * 1024 * 1024);
        Network network = new BasicNetwork(new HurlStack());
        requestQueue = new RequestQueue(cache, network);
        requestQueue.start();
    }
    return requestQueue;
}

public ImageLoader getImageLoader() {
    return imageLoader;
}

从 url 加载图片，如下所示

私有(private)无效 loadImage(){

String url = editTextUrl.getText().toString().trim();
imageLoader = CustomVolleyRequest.getInstance(this.getApplicationContext())
            .getImageLoader();
imageLoader.get(url, ImageLoader.getImageListener(imageView,
       R.drawable.image, android.R.drawable.ic_dialog_alert));
imageView.setImageUrl(url, imageLoader);

不需要为此使用处理程序。