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android - FrameManager 返回 NullPointer 异常

问题描述

我从我的容器活动中访问了底部导航视图，并将项目选择的侦听器设置为底部导航视图。以下代码在我的 onCreateView 片段中。

b2 = (BottomNavigationView) getActivity().findViewById(R.id.botttom_nav);

b2.setOnNavigationItemSelectedListener(new BottomNavigationView.OnNavigationItemSelectedListener() {
        @Override
        public boolean onNavigationItemSelected(@NonNull MenuItem menuItem) {
            Fragment selectedFragment = null;

            switch (menuItem.getItemId()){
                case R.id.songs:
                    selectedFragment=new SongsFragment();
                    break;
                case R.id.albums:
                    selectedFragment=new AlbumFragment();
                    break;
                case R.id.artists:
                    selectedFragment=new ArtistFragment();
                    Bundle bundle = new Bundle();
                    bundle.putStringArrayList("artists",songArtists);
                    selectedFragment.setArguments(bundle);
                    break;
                case R.id.playlists:
                    selectedFragment=new PlaylistsFragment();
                    break;
            }
            FragmentManager fragmentManager = getActivity().getSupportFragmentManager();
            FragmentTransaction fragmentTransaction = fragmentManager.beginTransaction();
            fragmentTransaction.replace(R.id.frame_main,selectedFragment).commit();
            return true;
        }
    });

显示 fragmentmanager 错误。

错误日志如下所示：

PID: 22518
java.lang.NullPointerException: Attempt to invoke virtual method 'android.support.v4.app.FragmentManager android.support.v4.app.FragmentActivity.getSupportFragmentManager()' on a null object reference
    at com.noob.audioplayer.SongsFragment$2.onNavigationItemSelected(SongsFragment.java:215)
    at android.support.design.widget.BottomNavigationView$1.onMenuItemSelected(BottomNavigationView.java:204)
    at android.support.v7.view.menu.MenuBuilder.dispatchMenuItemSelected(MenuBuilder.java:840)
    at android.support.v7.view.menu.MenuItemImpl.invoke(MenuItemImpl.java:158)
    at android.support.v7.view.menu.MenuBuilder.performItemAction(MenuBuilder.java:991)
    at android.support.design.internal.BottomNavigationMenuView$1.onClick(BottomNavigationMenuView.java:115)
    at android.view.View.performClick(View.java:6597)
    at android.view.View.performClickInternal(View.java:6574)
    at android.view.View.access$3100(View.java:778)
    at android.view.View$PerformClick.run(View.java:25885)
    at android.os.Handler.handleCallback(Handler.java:873)
    at android.os.Handler.dispatchMessage(Handler.java:99)

标签： androidandroid-fragmentsnullpointerexceptionandroid-fragmentactivity

解决方案

在您的代码getActivity()中为空，因此您需要显示片段的活动的上下文。

在您的片段中声明一个变量

private YOUR_Activity myContext;

然后在片段覆盖onAttach()

@Override
public void onAttach(Activity activity) {
   myContext=(YOUR_Activity) activity;
   super.onAttach(activity);
}

然后你supportFragmentManager这样打电话

FragmentManager fragmentManager = myContext.getSupportFragmentManager();

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