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我有带有 ViewPager 的 TabLayout 包括 3 个选项卡/片段。

每次恢复时，我都需要向每个片段添加操作。使用触摸更改片段时一切正常，但是当我以编程方式更改选项卡时，应用程序崩溃。我应该怎么做才能防止这个问题？

这是一些代码来解释我的问题。

private TabLayout tabLayout;

@Override
public void onResume() {
    super.onResume();

    //This part works when first tab is selected
    int chatSelTab = 0;
    TabLayout.Tab selectedTab = tabLayout.getTabAt(chatSelTab);
    selectedTab.select();
}



private void setupTablayout() {
    tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.persons)));
    tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.groups)));
    tabLayout.addTab(tabLayout.newTab().setText(getString(R.string.online)));

    tabLayout.setTabGravity(TabLayout.GRAVITY_FILL);

    final ViewPager viewPager = (ViewPager) findViewById(R.id.pager);
    final PagerAdapter adapter = new PagerAdapter
            (getSupportFragmentManager(), tabLayout.getTabCount(), this);
    viewPager.setAdapter(adapter);
    viewPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(tabLayout));

    tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            Voids.savePreferences(getApplicationContext(), Voids.CHAT_SELECTED_TAB, tab.getPosition());
            viewPager.setCurrentItem(tab.getPosition());
            switch (tab.getPosition()) {
                case 1:

                    /* TODO: app crashes here when programmatically select tab nro 1. */

                    SwipeRefreshLayout swipeRefreshLayout = (SwipeRefreshLayout) activity.findViewById(R.id.swipeRefresh);
                    swipeRefreshLayout.setOnRefreshListener(new SwipeRefreshLayout.OnRefreshListener() {
                        @Override
                        public void onRefresh() {
                            // DO MY STUFF
                        }
    });
                    break;
            }
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {

        }

        @Override
        public void onTabReselected(TabLayout.Tab tab) {

        }
    });
}

这就是我对 logcat 的了解

08-25 01:20:45.054  31753-31753/com.myapp E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.myapp, PID: 31753
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v4.widget.SwipeRefreshLayout.setOnRefreshListener(android.support.v4.widget.SwipeRefreshLayout$OnRefreshListener)' on a null object reference
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1 回答 1

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如果您的 SwipeRefreshLayout 是 on Fragment1，那么您为什么要这样做：

SwipeRefreshLayout swipeRefreshLayout = (SwipeRefreshLayout) activity.findViewById(R.id.swipeRefresh);

？？？

您正在尝试从活动的视图层次结构中查找视图。即使 Activity 用作 Fragment 占位符，也不包括后者的视图层次结构。您还需要从中获取swipeRefreshLayout参考Fragment1并处理其上的逻辑。

于 2016-01-05T17:19:12.427 回答