如何仅在单击第二个选项卡时才显示此 Toast 消息

Question

我有一个导航栏，有三个选项卡，每个选项卡都是一个片段。我在第二个片段的onCreateView方法中写了这条吐司消息：

public class SecondFragment extends Fragment{
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        View rootView=inflater.inflate(R.layout.second_layout,container,false);

        Toast.makeText(getContext(), "Test", Toast.LENGTH_LONG).show();
        return rootView;
    }

我想要的是，只有当我单击此选项卡时，才会显示消息。但问题是，如果我启动应用程序，消息会直接显示，但为什么呢？

这是我的主要活动.java：

public class MainActivity extends AppCompatActivity{
    NavigationView mNavigationView;
    FragmentManager mFragmentManager;
    FragmentTransaction mFragmentTransaction;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        /**
         *Setup the DrawerLayout and NavigationView
         */
        mNavigationView = (NavigationView) findViewById(R.id.shitstuff) ;
        /**
         * Lets inflate the very first fragment
         * Here , we are inflating the TabFragment as the first Fragment
         */
        mFragmentManager = getSupportFragmentManager();
        mFragmentTransaction = mFragmentManager.beginTransaction();
        mFragmentTransaction.replace(R.id.containerView,new TabFragment()).commit();
    }

}

而且(我认为这对这个问题很重要(我的 TabFragment：

public class TabFragment extends Fragment {
    public static TabLayout tabLayout;
    public static ViewPager viewPager;
    public static int int_items = 3 ;
    @Nullable
    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {

        /**
         *Inflate tab_layout and setup Views.
         */
            View x =  inflater.inflate(R.layout.tab_layout,null);
            tabLayout = (TabLayout) x.findViewById(R.id.tabs);
            viewPager = (ViewPager) x.findViewById(R.id.viewpager);
        /**
         *Set an Apater for the View Pager
         */
        viewPager.setAdapter(new MyAdapter(getChildFragmentManager()));
        /**
         * Now , this is a workaround ,
         * The setupWithViewPager dose't works without the runnable .
         * Maybe a Support Library Bug .
         */
        tabLayout.post(new Runnable() {
            @Override
            public void run() {
                    tabLayout.setupWithViewPager(viewPager);
                   }
        });
        return x;
    }
    class MyAdapter extends FragmentPagerAdapter {
        public MyAdapter(FragmentManager fm) {
            super(fm);
        }
        /**
         * Return fragment with respect to Position .
         */
        @Override
        public Fragment getItem(int position)
        {
            if(position == 0){
                return new FirstFragment();
            }
            if(position == 1){
                return new SecondFragment();
            }
            if(position == 2){
                return new ThirdFragment();
            }
        return null;
        }
        @Override
        public int getCount() {
            return int_items;
        }
        /**
         * This method returns the title of the tab according to the position.
         */
        @Override
        public CharSequence getPageTitle(int position) {
            switch (position){
                case 0 :
                    return "First";
                case 1 :
                    return "Second";
                case 2 :
                    return "Third";
            }
                return null;
        }
    }
}

那么我在哪里必须说Toast.makeText(getContext(), "Test", Toast.LENGTH_LONG).show();仅通过按第二个选项卡来显示它？

Answer 1

可以使用代码在显示 Toast 后终止它，以便在单击另一个片段时它不可见。

试试这个

toast = new Toast(getContext());
toast.cancel(); //this will prevent toast from displaying multiple times

希望它会起作用

Answer 2

等等！ 如果您有多个选项卡，则每个选项卡必须包含单独的片段，并且对于每个片段，都有Java类和一个相同的布局文件，然后编码部分将在创建Java文件中，XML/布局部分将位于.xml文件中。