ViewPager 无法使用 Picasso 懒惰地加载图像 [英] ViewPager unable to load images lazily with Picasso

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.

ViewPager 的 setAdapter() 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. ViewPager 的 Fragment 的 onCreateView() 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;
}

ViewPager的Fragments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);      

}        

FragmentPagerAdapter的onInstantiateItem()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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