ViewPager 无法使用 Picasso 懒惰地加载图像

ViewPager unable to load images lazily with Picasso(ViewPager 无法使用 Picasso 懒惰地加载图像)

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问题描述

我在 TabHost 的第一个选项卡中有一个 FragmentActivity,而 FragmentActivity 本身包含一个 ViewPager.

I have a FragmentActivity in the first tab of a TabHost, and the FragmentActivity itself holds a ViewPager.

ViewPagersetAdapter() 方法使用一组 Fragment 设置 FragmentPagerAdapter.目标是在 TabHost 的第一个窗格中显示可滑动的图像.

The ViewPager's setAdapter() method sets a FragmentPagerAdapter with a set of Fragments. The goal is to have swipeable images in the first pane of the TabHost.

为了测试它,我加载了我在项目的 drawable 目录中本地保存的一堆图像.一切都很顺利.

To test it, I was loading a bunch of images that I had kept locally in the project's drawable directory. Everything worked beautifully.

在测试了这个初始设置之后,我正在从 REST Web 服务下载一堆图像 URL.我希望这些图像在 ViewPager 中延迟加载,我尝试在三个地方调用 Picasso 的 load() 方法:

After having tested this initial setup, I'm downloading a bunch of image URLs' off a REST web service. I want these images to load lazily in the ViewPager, and I tried calling Picasso's load() method in three places:

  1. ViewPagerFragmentonCreateView() 方法(与我之前从中加载图像的位置相同)本地 drawable 目录).

  1. The onCreateView() method of the ViewPager's Fragments (the same place where I was earlier loading images from the local drawable directory).

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, 
    Bundle savedInstanceState) {                

    View myFragmentView = inflater.inflate(R.layout.layout_fragment, container, false);

    ImageView imageView = (ImageView)getView().findViewById(R.id.fragment_image);
    String url = getArguments().getString(IMAGE_RESOURCE_URL);
    Context context = getActivity();
    Picasso.with(context).load(url).fit().into(imageView);

    return myFragmentView;
}

  • ViewPagerFragments的onViewCreated()方法.

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState){
    
        Context context = getActivity();
        String url = getArguments().getString(IMAGE_RESOURCE_URL);
        ImageView imageView = (ImageView)view.findViewById(R.id.fragment_image);
        Picasso.with(context).load(url).fit().into(imageView);      
    
    }        
    

  • FragmentPagerAdapteronInstantiateItem()方法.

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
    
        View v = inflater.inflate(R.layout.layout_fragment, container, false);
        Context context = Tab1Activity.this;
        String url = getItem(position).getArguments().getString("IMAGE_RESOURCE_URL");
        ImageView imageView = (ImageView)v.findViewById(R.id.fragment_image);
        Picasso.with(context).load(url).fit().into(imageView);
        return v;
    }
    

  • 这些方法都不起作用.我知道毕加索不是问题,因为前几天我尝试在 ListView 中使用毕加索,它就像一个魅力.我做错了什么?

    None of these methods worked. I know that its not a problem with Picasso because the other day I tried using Picasso in a ListView and it worked like a charm. What am I doing wrong ?

    推荐答案

    您的第一种方法应该可以正常工作...如果您正确实施它.我希望您的代码会因 NullPointerException 而崩溃.

    Your first approach should work fine... if you implement it correctly. I would expect your code to crash with a NullPointerException.

    替换:

    ImageView imageView = (ImageView)getView().findViewById(R.id.fragment_image);
    

    与:

    ImageView imageView = (ImageView)myFragmentView.findViewById(R.id.fragment_image);
    

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