Question

如何在“活动”中从“片段”中调用Toast？当我尝试时，我有这个error: Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.String android.content.Context.getPackageName()' on a null object reference 下面是我的整个Activity类，片段和Logcat。

活动

public class MainActivity extends AppCompatActivity {
private  TabsAdapter tabsAdapter;
private TabLayout tabLayout;
private ViewPager viewPager;

private  int [] tabicons = {
        R.drawable.money,
        R.drawable.gold
};
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    viewPager= findViewById(R.id.pager);
    tabLayout= findViewById(R.id.tab_layout);

    tabsAdapter= new TabsAdapter(getSupportFragmentManager());
    tabsAdapter.addFragment(new Fragment1(),"Kursy Walut");
    tabsAdapter.addFragment(new Fragment2(),"Kursy Złota");
  //  tabsAdapter.addFragment(new Fragment3(),"Tab 3");


    viewPager.setAdapter(tabsAdapter);
    tabLayout.setupWithViewPager(viewPager);

    setupTabIcons();

    Fragment2 fragment2= new Fragment2();
    fragment2.MetodaFragmentu();
}
private void setupTabIcons() {
    if (tabLayout!=null){
        if (tabLayout.getTabAt(0)!=null)
            tabLayout.getTabAt(0).setIcon(tabicons[0]);
        if (tabLayout.getTabAt(1)!=null)
            tabLayout.getTabAt(1).setIcon(tabicons[1]);
        if (tabLayout.getTabAt(2)!=null)
            tabLayout.getTabAt(2).setIcon(tabicons[2]);
    }
}

}

片段

public class Fragment2 extends Fragment {

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState){


    return inflater.inflate(R.layout.layout_fragment_2, container,false);
}

public void MetodaFragmentu(){

    Toast.makeText(getActivity(),"Ok",Toast.LENGTH_LONG).show();
}
}

Logcat

2019-05-20 12：05：52.040 10566-10566 / com.example.goldandcurrency E / AndroidRuntime：FATAL EXCEPTION：main 流程：com.example.goldandcurrency，PID：10566 java.lang.RuntimeException：无法启动活动ComponentInfo {com.example.goldandcurrency / com.example.goldandcurrency.MainActivity}：java.lang.NullPointerException：尝试调用虚拟方法'java.lang.String android.content.Context。空对象引用上的getPackageName（）' 在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2665）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2726）在android.app.ActivityThread.-wrap12（ActivityThread.java）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1477）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:154）在android.app.ActivityThread.main（ActivityThread.java:6119）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:886）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:776）原因：java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'java.lang.String android.content.Context.getPackageName（）' 在android.widget.Toast（Toast.java:103）在android.widget.Toast.makeText（Toast.java:256）在com.example.goldandcurrency.Fragment2.MetodaFragmentu（Fragment2.java:29）在com.example.goldandcurrency.MainActivity.onCreate（MainActivity.java:40）在android.app.Activity.performCreate（Activity.java:6679）在android.app.Instrumentation.callActivityOnCreate（Instrumentation.java:1118）在android.app.ActivityThread.performLaunchActivity（ActivityThread.java:2618）在android.app.ActivityThread.handleLaunchActivity（ActivityThread.java:2726）在android.app.ActivityThread.-wrap12（ActivityThread.java）在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:1477）在android.os.Handler.dispatchMessage（Handler.java:102）在android.os.Looper.loop（Looper.java:154）在android.app.ActivityThread.main（ActivityThread.java:6119）在java.lang.reflect.Method.invoke（本机方法）在com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:886） com.android.internal.os.ZygoteInit.main（ZygoteInit.java:776）

从活动片段中吐司

0 个答案: