在ViewPager中的片段上调用方法 [英] call a method on a fragment in a ViewPager

问题描述

我要做的就是调用Fragment类的函数.但是我似乎找不到一种方法来访问ViewPager中的片段实例.

All I want to do is calling a function of my Fragment's class. But I can't seem to find a way to access the instance of my fragments which are in a ViewPager.

我的活动的xml:

<android.support.v4.view.ViewPager xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:id="@+id/pager"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".MainActivity" />

没有，所以我不能打电话给findFragmentById()(可以吗?) 我也不知道该给findFragmentByTag()什么，它总是返回null:/

There is no so I can't call findFragmentById() (can I?) also I don't know what to give to findFragmentByTag(), it always return null :/

推荐答案

pagerAdapter.getItem(int)方法通常会创建该片段的新实例，因此，您可以使用HashMap来存储对已经存在的片段.

The pagerAdapter.getItem(int) method usually creates a new instance of the fragment, however, so what you can do is use a HashMap to store a reference to the already existing fragments.

// ViewPagerAdapter
private HashMap<Integer, Fragment> fragmentHashMap = new HashMap<>();

@Override
public Fragment getItem(int position) {
    if (fragmentHashMap.get(position) != null) {
        return fragmentHashMap.get(position);
    }
    TabFragment tabFragment = new TabFragment();
    fragmentHashMap.put(position, tabFragment);
    return tabFragment;
}

然后，您可以找到片段来调用其方法:

Then you can find your fragment to call its methods:

FragmentAdapter fa = (FragmentAdapter)viewPager.getAdapter();
TabFragment theFragment = (TabFragment)fa.getItem(index);
theFragment.customMethod(Object obj);

您将必须跟踪哪个片段与哪个索引一起使用，因为将它们强制转换为它们的特定类才能访问它们的方法.

You will have to keep track of which fragment goes with which index because you cast them to their specific class in order to access their methods.

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