java如何在不点击的情况下显示片段

Question

我有一个带有两个选项卡的Tablelayout，在我编写的代码中，当我单击选项卡时，它们会显示出来。现在它是这样工作的：我打开活动，在单击TabLayout标题之前，不会显示TabLayout中的片段。我如何使其在打开activity-fragment时已经可见

public class DetailActivity extends AppCompatActivity {

    FrameLayout simpleFrameLayout;
    TabLayout tabLayout;
    ImageView onBackPressed;

    Button subsButton;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_detail);


        if (getSupportActionBar() != null) {
            getSupportActionBar().hide();
        }


        subsButton = findViewById(R.id.subsButton);

        subsButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                if (subsButton.getText().equals("Подписаться")) {

                    subsButton.setText("Отписаться");
                    subsButton.setBackgroundColor(subsButton.getContext().getResources().getColor(R.color.colorGrey));


                } else if (subsButton.getText().equals("Отписаться")) {
                    subsButton.setText("Подписаться");
                    subsButton.setBackgroundColor(subsButton.getContext().getResources().getColor(R.color.colorPrimary));

                }

            }
        });


        simpleFrameLayout = (FrameLayout) findViewById(R.id.simpleFrameLayout);
        tabLayout = (TabLayout) findViewById(R.id.simpleTabLayout);

        onBackPressed = (ImageView) findViewById(R.id.onBackPressed);

        tabLayout.selectTab(tabLayout.getTabAt(0));

        TabLayout.Tab firstTab = tabLayout.newTab();
        firstTab.setText("Chelsea");
        tabLayout.addTab(firstTab);


        TabLayout.Tab secondTab = tabLayout.newTab();
        secondTab.setText("Manchester City");
        tabLayout.addTab(secondTab);


        tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {


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

                Fragment fragment = null;
                switch (tab.getPosition()) {
                    case 0:
                        fragment = new FragmentHisOne();
                        break;
                    case 1:
                        fragment = new FragmentHisTwo();
                        break;
                    default:
                        fragment = new FragmentHisOne();
                        break;
                }
                FragmentManager fm = getSupportFragmentManager();
                FragmentTransaction ft = fm.beginTransaction();
                ft.replace(R.id.simpleFrameLayout, fragment);
                ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
                ft.commit();

            }

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


            }

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

            }
        });
    }


    public void onBackPressed(View view) {
        Intent intent = new Intent(view.getContext(), MainActivity.class);
        view.getContext().startActivity(intent);
    }

Answer 1

您选择该选项卡之前甚至没有添加它。 表格布局。选择tab（tabLayout.getTabAt（0））；添加选项卡后移动此代码

Answer 2

事实上，在创建TabLayout选项卡之前，我没有预先创建默认片段。我的解决方案：

FrameLayout simpleFrameLayout;
    TabLayout tabLayout;
    ImageView onBackPressed;

    Button subsButton;

    Fragment fragment = null;
    FragmentManager fragmentManager;
    FragmentTransaction fragmentTransaction;


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_detail);


        if (getSupportActionBar() != null) {
            getSupportActionBar().hide();
        }


        subsButton = findViewById(R.id.subsButton);

        subsButton.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View view) {
                if (subsButton.getText().equals("Подписаться")) {

                    subsButton.setText("Отписаться");
                    subsButton.setBackgroundColor(subsButton.getContext().getResources().getColor(R.color.colorGrey));


                } else if (subsButton.getText().equals("Отписаться")) {
                    subsButton.setText("Подписаться");
                    subsButton.setBackgroundColor(subsButton.getContext().getResources().getColor(R.color.colorPrimary));

                }

            }
        });


        simpleFrameLayout = (FrameLayout) findViewById(R.id.simpleFrameLayout);
        tabLayout = (TabLayout) findViewById(R.id.simpleTabLayout);

        onBackPressed = (ImageView) findViewById(R.id.onBackPressed);

        tabLayout.selectTab(tabLayout.getTabAt(0));

        TabLayout.Tab firstTab = tabLayout.newTab();
        firstTab.setText("Chelsea");
        tabLayout.addTab(firstTab);


        TabLayout.Tab secondTab = tabLayout.newTab();
        secondTab.setText("Manchester City");
        tabLayout.addTab(secondTab);

        fragment = new FragmentHisOne();
        fragmentManager = getSupportFragmentManager();
        fragmentTransaction = fragmentManager.beginTransaction();
        fragmentTransaction.replace(R.id.simpleFrameLayout, fragment);
        fragmentTransaction.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
        fragmentTransaction.commit();

        tabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {


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

                Fragment fragment = null;
                switch (tab.getPosition()) {
                    case 0:
                        fragment = new FragmentHisOne();
                        break;
                    case 1:
                        fragment = new FragmentHisTwo();
                        break;
                    default:
                        fragment = new FragmentHisOne();
                        break;
                }
                FragmentManager fm = getSupportFragmentManager();
                FragmentTransaction ft = fm.beginTransaction();
                ft.replace(R.id.simpleFrameLayout, fragment);
                ft.setTransition(FragmentTransaction.TRANSIT_FRAGMENT_OPEN);
                ft.commit();

            }

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


            }

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

            }
        });
    }


    public void onBackPressed(View view) {
        Intent intent = new Intent(view.getContext(), MainActivity.class);
        view.getContext().startActivity(intent);
    }

    public void subsButton(View view) {
        //Button.setBackground
    }