Android ViewPager 不会显示第二页？

Question

我正在使用 ViewPager 滑动屏幕的一部分（而不是整个 View/Page）。

我可以将 isViewFromObject 修改为 return true，然后我的第一张图片出现，但第二张图片无法加载。对我在这里缺少的东西有什么想法吗？我在想我的 isViewFromObject 方法或实例化项目中的 for 循环仍然有问题。

注意：有意不使用扩展 FragmentStatePagerAdapter 和扩展常规 PagerAdapter。

private class ScreenSlidePagerAdapter extends PagerAdapter {

        public ScreenSlidePagerAdapter() {}


        @Override
        public Object instantiateItem (ViewGroup container, int position) {
            LayoutInflater inflater = (LayoutInflater) container.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 

            int RLayoutId;
            RLayoutId = R.layout.images_to_show; //an XML with just a LinearLayout

            ViewGroup imageLayout = (ViewGroup) inflater.inflate(RLayoutId, null);

            for (position = 0; position < mImageURLArraylist.size(); position++) { 
                container.addView(insertPhoto("http:" + mImageURLArraylist.get(position) ) ); 
                        }//end of for loop
            return imageLayout;

        }

        @Override
        public boolean isViewFromObject (View view, Object obj) { //Object parameter is received from instantiateItem(ViewGroup, int)
//loads the first image successfully if i just do return true. 
//doesn't load any of my images when I do return view == ( (View) obj);

                }


        //one of four methods that you must override when using pageradapters
        @Override
        public int getCount() {
            //tested in debugging and this has the correct size (2)
            return mImageURLArraylist.size(); //the number of pages the adapter will create.
                }

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

    }//end of ScreenSlidePagerAdapter

我在上面的 instantiateItem 中执行的 insertPhoto 方法：

public View insertPhoto(String path){
        LinearLayout layout = new LinearLayout(getActivity());
        layout.setGravity(Gravity.CENTER);
        ImageView imageView = new ImageView(getActivity());
        imageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
        Picasso.with(getActivity() ).load(path).into(imageView); //tried this but got errors when running > resize(layout.getWidth(), layout.getHeight()), also tried .fit() after .load image wouldn't load
        layout.addView(imageView);
        return layout;        
}

Answer 1

您需要将视图添加到容器中。尝试按此处所示更改您的方法：

    @Override
    public Object instantiateItem (ViewGroup container, int position) {
        LayoutInflater inflater = (LayoutInflater) container.getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 

        int RLayoutId;
        RLayoutId = R.layout.images_to_show; //an XML with just a LinearLayout

        ViewGroup imageLayout = (ViewGroup) inflater.inflate(RLayoutId, container, false);

        container.addView(insertPhoto(imageLayout, "http:" + mImageURLArraylist.get(position) ));
        return imageLayout;

    }

// this needs to be refactored, too many viewgroups. Move all layouts to XML
public View insertPhoto(ViewGroup root, String path){
    LinearLayout layout = new LinearLayout(getActivity());
    layout.setGravity(Gravity.CENTER);
    ImageView imageView = new ImageView(getActivity());
    imageView.setScaleType(ImageView.ScaleType.CENTER_INSIDE);
    Picasso.with(getActivity() ).load(path).into(imageView); //tried this but got errors when running > resize(layout.getWidth(), layout.getHeight()), also tried .fit() after .load image wouldn't load
    layout.addView(imageView);
    root.addView(layout);
    return root;        
}

如果您的布局全部在 XML 中完成就更好了，因此 insertPhoto 函数只需调用 Picasso 来加载图像。

Answer 2

每个页面都会调用PagerAdapter的instantiateItem()方法，所以容器中只能插入一个page/child。

    @Override
    public Object instantiateItem (ViewGroup container, int position) {
        final View page = insertPhoto("http:" + mImageURLArraylist.get(position) );
        container.addView(page); 
        return page;
    }

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

Android ViewPager 不会显示第二页？

Android ViewPager Won't Show Second Page?

android

android-viewpager

android-pageradapter