玩安卓---Fragment

public class MainActivity extends WanAndroidBaseActivity {

    @BindView(R.id.navigationView)
    BottomNavigationView bottomNavigationView;
    private List<Fragment> fragmentList;
    private FragmentTransaction transaction;
    private int lastFragment;

    @Override
    protected int getLayoutId() {
        return R.layout.activity_main;
    }

    @Override
    protected void initView() {
        initFragment();
        lastFragment = 0;

        // replace(int,fragment): 替换一个已被添加进视图容器的Fragment，缺点是每次都会重新初始化加载
        transaction.replace(R.id.mainContainer, fragmentList.get(lastFragment));
        // show(fragment): 显示一个存在fragment
        // hide(fragment): 隐藏一个存在的fragment
        transaction.show(fragmentList.get(lastFragment));
        // 提交事务
        transaction.commit();

        bottomNavigationView.setOnNavigationItemSelectedListener(menuItem -> {
            switch (menuItem.getItemId()) {
                case R.id.menu_home:
                    if (lastFragment != 0) {
                        switchFragment(lastFragment, 0);
                        lastFragment = 0;
                    }
                    break;
                case R.id.menu_knowledge_hierarchy:
                    if (lastFragment != 1) {
                        switchFragment(lastFragment, 1);
                        lastFragment = 1;
                    }
                    break;
                case R.id.menu_wechat_sub:
                    if (lastFragment != 2) {
                        switchFragment(lastFragment, 2);
                        lastFragment = 2;
                    }
                    break;
                case R.id.menu_project:
                    if (lastFragment != 3) {
                        switchFragment(lastFragment, 3);
                        lastFragment = 3;
                    }
                    break;
                case R.id.menu_me:
                    if (lastFragment != 4) {
                        switchFragment(lastFragment, 4);
                        lastFragment = 4;
                    }
                    break;
                default:
                    return true;
            }
            return true;
        });
    }

    private void initFragment() {
        fragmentList = new ArrayList<>();
        fragmentList.add(new HomeFragment());
        fragmentList.add(new HomeFragment());
        fragmentList.add(new HomeFragment());
        fragmentList.add(new HomeFragment());
        fragmentList.add(new HomeFragment());
        transaction = getSupportFragmentManager().beginTransaction();
    }

    /**
     * 切换Fragment
     *
     * @param lastFragment
     * @param currentIndex
     */
    private void switchFragment(int lastFragment, int currentIndex) {
        // hide(fragment): 隐藏fragment
        transaction.hide(fragmentList.get(lastFragment));
        if (!fragmentList.get(currentIndex).isAdded()) {
            // add(): 像Activity state中添加一个Fragment
            // remove(): 像Activity state中移除一个Fragment
            transaction.add(R.id.mainContainer, fragmentList.get(currentIndex));
        }
        transaction.show(fragmentList.get(currentIndex));
        // commitAllowingStateLoss: 和commit一样，但是允许Activity的状态保存之后提交
        transaction.commitAllowingStateLoss();
    }


}

注意Fragment中的几个方法的使用