java - 如何使用多态性在运行时根据实例加载 fragment ？

Question

我有一个选项卡布局，其中包含 3 个选项卡项，每个选项卡项都有自己的 fragment ，可以在选择时在运行时加载。

MainActivity.class:这里根据所选选项卡的位置调用LoadFragment。

tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                switch (tab.getPosition()) {
                    case 0:
                        LoadFragment(new LocationFragment());
                        break;
                    case 1:
                        LoadFragment(new InformationFragment());
                        break;
                    case 2:
                        LoadFragment(new CommentsFragment());
                        break;
                }
            }

我的问题是如何使用 switch 语句作为逻辑来使用 fragment 管理器加载正确的 fragment ？我不想有 if else 语句层次结构。

private void LoadFragment(Fragment fragment) {
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();

        switch (*some logic here*) {

            case fragment instanceof LocationFragment:
                Log.i("MainActivity", "inside load fragment");
                ft.replace(R.id.coordinate_layout, new LocationFragment());
                break;


            case fragment instanceof InformationFragment:
                ft.replace(R.id.coordinate_layout, new InformationFragment());
                break;


            case fragment instanceof CommentsFragment:
                ft.replace(R.id.coordinate_layout, new CommentsFragment());
                break;

            ft.commit();

        }
    }

Answer 1

您不需要多次创建实例，您只需传递类型即可，在加载时您可以决定需要加载哪个 fragment 。

    private static final int TYPE_LOCATION=0;
    private static final int TYPE_INFO=1;
    private static final int TYPE_COMMENT=2;

tabLayout.addOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
            @Override
            public void onTabSelected(TabLayout.Tab tab) {
                switch (tab.getPosition()) {
                    case 0:
                        LoadFragment(TYPE_LOCATION);
                        break;
                    case 1:
                        LoadFragment(TYPE_INFO);
                        break;
                    case 2:
                        LoadFragment(TYPE_COMMENT);
                        break;
                }
            }

private void LoadFragment(int typeOfFragment) {
        Log.i("MainActivity", "inside load fragment");
        FragmentTransaction ft = getSupportFragmentManager().beginTransaction();

        switch (typeOfFragment) {

            case TYPE_LOCATION:   
              ft.replace(R.id.coordinate_layout, new LocationFragment());
                break;


            case TYPE_INFO:
                ft.replace(R.id.coordinate_layout, new InformationFragment());
                break;


            case TYPE_COMMENT:
                ft.replace(R.id.coordinate_layout, new CommentsFragment());
                break;

            ft.commit();

        }
    }