从 ViewPager 中检索片段 [英] Retrieve a Fragment from a ViewPager

问题描述

我使用 ViewPager 和 FragmentStatePagerAdapter 来托管三个不同的片段:

I'm using a ViewPager together with a FragmentStatePagerAdapter to host three different fragments:

• [片段1]
• [片段 2]
• [片段3]

当我想从 FragmentActivity 中的 ViewPager 获取 Fragment1 时.

When I want to get Fragment1 from the ViewPager in the FragmentActivity.

有什么问题，我该如何解决?

What is the problem, and how do I fix it?

推荐答案

主要答案依赖于框架生成的名称.如果这种情况发生变化，它将不再起作用.

The main answer relies on a name being generated by the framework. If that ever changes, then it will no longer work.

这个解决方案怎么样，覆盖 Fragment(State)PagerAdapter 的 instantiateItem() 和 destroyItem():

What about this solution, overriding instantiateItem() and destroyItem() of your Fragment(State)PagerAdapter:

public class MyPagerAdapter extends FragmentStatePagerAdapter {
    SparseArray<Fragment> registeredFragments = new SparseArray<Fragment>();

    public MyPagerAdapter(FragmentManager fm) {
        super(fm);
    }

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

    @Override
    public Fragment getItem(int position) {
        return MyFragment.newInstance(...); 
    }

    @Override
    public Object instantiateItem(ViewGroup container, int position) {
        Fragment fragment = (Fragment) super.instantiateItem(container, position);
        registeredFragments.put(position, fragment);
        return fragment;
    }

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        registeredFragments.remove(position);
        super.destroyItem(container, position, object);
    }

    public Fragment getRegisteredFragment(int position) {
        return registeredFragments.get(position);
    }
}

在处理可用的 Fragment 时，这似乎对我有用.尚未实例化的片段在调用 getRegisteredFragment 时将返回 null.但我一直在使用它主要是为了从 ViewPager 中获取当前的 Fragment:adapater.getRegisteredFragment(viewPager.getCurrentItem()) 和这不会返回 null.

This seems to work for me when dealing with Fragments that are available. Fragments that have not yet been instantiated, will return null when calling getRegisteredFragment. But I've been using this mostly to get the current Fragment out of the ViewPager: adapater.getRegisteredFragment(viewPager.getCurrentItem()) and this won't return null.

我不知道此解决方案的任何其他缺点.如果有的话，我想知道.

I'm not aware of any other drawbacks of this solution. If there are any, I'd like to know.

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