我正在关注 this tutorial用于在我的项目中实现 ViewPager。我已经成功地使用静态图像 做到了这一点。现在我想更改它，以便从 urls 检索图像并显示在 ViewPager 中。下面是我的代码。

Where should I add the method for downloading images and how to set it to my ViewPager?

任何帮助将不胜感激。

主要 Activity :

public class MainActivity extends AppCompatActivity {

    private ArrayList<Integer> images;
    private BitmapFactory.Options options;
    private ViewPager viewPager;
    private View btnNext, btnPrev;
    private FragmentStatePagerAdapter adapter;
    private LinearLayout thumbnailsContainer;
    private final static int[] resourceIDs = new int[]{R.mipmap.a, R.mipmap.b,
            R.mipmap.c, R.mipmap.d, R.mipmap.e, R.mipmap.f, R.mipmap.g};

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        images = new ArrayList<>();

        //find view by id
        viewPager = (ViewPager) findViewById(R.id.view_pager);
        thumbnailsContainer = (LinearLayout) findViewById(R.id.container);
        btnNext = findViewById(R.id.next);
        btnPrev = findViewById(R.id.prev);

        btnPrev.setOnClickListener(onClickListener(0));
        btnNext.setOnClickListener(onClickListener(1));

        setImagesData();

        // init viewpager adapter and attach
        adapter = new ViewPagerAdapter(getSupportFragmentManager(), images);
        viewPager.setAdapter(adapter);

        inflateThumbnails();
    }

    private View.OnClickListener onClickListener(final int i) {
        return new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                if (i > 0) {
                    //next page
                    if (viewPager.getCurrentItem() < viewPager.getAdapter().getCount() - 1) {
                        viewPager.setCurrentItem(viewPager.getCurrentItem() + 1);
                    }
                } else {
                    //previous page
                    if (viewPager.getCurrentItem() > 0) {
                        viewPager.setCurrentItem(viewPager.getCurrentItem() - 1);
                    }
                }
            }
        };
    }

    private void setImagesData() {
        for (int i = 0; i < resourceIDs.length; i++) {
            images.add(resourceIDs[i]);
        }
    }

    private void inflateThumbnails() {
        for (int i = 0; i < images.size(); i++) {
            View imageLayout = getLayoutInflater().inflate(R.layout.item_image, null);
            ImageView imageView = (ImageView) imageLayout.findViewById(R.id.img_thumb);
            imageView.setOnClickListener(onChagePageClickListener(i));
            options = new BitmapFactory.Options();
            options.inSampleSize = 3;
            options.inDither = false;
            Bitmap bitmap = BitmapFactory.decodeResource(getResources(), images.get(i), options );
            imageView.setImageBitmap(bitmap);
            //set to image view
            imageView.setImageBitmap(bitmap);
            //add imageview
            thumbnailsContainer.addView(imageLayout);
        }
    }

    private View.OnClickListener onChagePageClickListener(final int i) {
        return new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                viewPager.setCurrentItem(i);
            }
        };
    }
}

PageFragment 类:

   public class PageFragment extends Fragment {

        private int imageResource;
        private Bitmap bitmap;

        public static PageFragment getInstance(int resourceID) {
            PageFragment f = new PageFragment();
            Bundle args = new Bundle();
            args.putInt("image_source", resourceID);
            f.setArguments(args);
            return f;
        }

        @Override
        public void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            imageResource = getArguments().getInt("image_source");
        }

        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
            return inflater.inflate(R.layout.fragment_page, container, false);
        }

        @Override
        public void onViewCreated(View view, Bundle savedInstanceState) {
            super.onViewCreated(view, savedInstanceState);
            ImageView imageView = (ImageView) view.findViewById(R.id.image);

            BitmapFactory.Options o = new BitmapFactory.Options();
            o.inSampleSize = 4;
            o.inDither = false;
            bitmap = BitmapFactory.decodeResource(getResources(), imageResource, o);
            imageView.setImageBitmap(bitmap);
        }

        @Override
        public void onDestroy() {
            super.onDestroy();
            bitmap.recycle();
            bitmap = null;
        }
    }

ViewPager Adapter class:

public class ViewPagerAdapter extends FragmentStatePagerAdapter {

    private List<Integer> images;

    public ViewPagerAdapter(FragmentManager fm, List<Integer> imagesList) {
        super(fm);
        this.images = imagesList;
    }

    @Override
    public Fragment getItem(int position) {
        return PageFragment.getInstance(images.get(position));
    }

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

最佳答案

要将 ViewPager 用于图像，您必须制作一个扩展 PagerAdapter 的适配器，如下所示:

public class ImagePagerAdapter extends PagerAdapter {

    Context context;
    LayoutInflater layoutInflater;

    ArrayList<String> arrayList;

    public ImagePagerAdapter(Context context, ArrayList<String> arrayList) {
        this.context = context;
        layoutInflater = (LayoutInflater) context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        this.arrayList = arrayList;
    }

    @Override
    public int getCount() {
        if(arrayList != null){
            return arrayList.size();
        }
        return 0;
    }

    @Override
    public boolean isViewFromObject(View view, Object object) {
        return view == ((LinearLayout) object);
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        View itemView = layoutInflater.inflate(R.layout.image_viewpager_layout, container, false);

        ImageView imageView = (ImageView) itemView.findViewById(R.id.viewPagerItem_image1);

        Picasso.with(context).load(arrayList.get(position))
                            .placeholder(R.drawable.image_uploading)
                            .error(R.drawable.image_not_found).into(imageView);

        container.addView(itemView);

        return itemView;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        container.removeView((LinearLayout) object);
    }

}

适配器的 xml 布局是:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" >


        <ImageView
            android:id="@+id/viewPagerItem_image1"
            android:layout_width="match_parent"
            android:layout_height="250dp"
            android:scaleType="fitXY"
            android:src="@drawable/ic_launcher"/>


</LinearLayout>

关于android - 在 ViewPager Android 中设置来自 url 的图像，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/33818873/