带有 ViewPager 的 TabLayout 未按预期工作

Question

我的申请中有 3 个 TabLayout 和 ViewPager。

如果我滑动以更改选项卡，那么它 的行为会很奇怪。

场景如下。

假设有 3 个选项卡 A、B、C。

启动应用程序时将打开默认选项卡 A。

从 A 转到 B - 工作正常。
从 B 转到 A - 工作正常。
从 A 转到 B - 工作正常。
从 B 转到 C - 工作正常。

现在问题从这里开始。
从 C 转到 B - 它会加载 A 和 B，但只显示 B。

Why A and B loads if I come from C ??

下面是我的代码。

private Toolbar toolbar;
    private TabLayout tabLayout;
    private ViewPager viewPager;
    ViewPagerAdapter adapter;

toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        getSupportActionBar().setDisplayHomeAsUpEnabled(false);

        viewPager = (ViewPager) findViewById(R.id.viewpager);
        setupViewPager(viewPager);
        tabLayout = (TabLayout) findViewById(R.id.tabs);
        tabLayout.setupWithViewPager(viewPager);

private void setupViewPager(ViewPager viewPager) {
        adapter = new ViewPagerAdapter(getSupportFragmentManager());
        adapter.addFragment(new FragmentOpen(), "OPEN");
        adapter.addFragment(new FragmentClose(), "CLOSE");
        adapter.addFragment(new FragmentTest(), "TEST");
        viewPager.setAdapter(adapter);
    }

    class ViewPagerAdapter extends FragmentPagerAdapter {
        private final List<Fragment> mFragmentList = new ArrayList<>();
        private final List<String> mFragmentTitleList = new ArrayList<>();

        public ViewPagerAdapter(FragmentManager manager) {
            super(manager);
        }

        @Override
        public Fragment getItem(int position) {
            return mFragmentList.get(position);
        }

        @Override
        public int getCount() {
            return mFragmentList.size();
        }

        public void addFragment(Fragment fragment, String title) {
            mFragmentList.add(fragment);
            mFragmentTitleList.add(title);
        }

        @Override
        public CharSequence getPageTitle(int position) {
            return mFragmentTitleList.get(position);
        }
    }

我想每次都加载标签。
为此，我使用以下代码。

viewPager.addOnPageChangeListener(new ViewPager.OnPageChangeListener() {
            @Override
            public void onPageScrolled(int position, float positionOffset, int positionOffsetPixels) {

            }

            @Override
            public void onPageSelected(int position) {
                if(adapter != null){
                    adapter.getItem(position).onResume();
                }
                Toast.makeText(getApplicationContext(), "Page Selected", Toast.LENGTH_LONG).show();
            }

            @Override
            public void onPageScrollStateChanged(int state) {

            }
        });

但当我来自 C 时，它总是会加载两个选项卡。

What I want is: only Tab B must load when came from C, not Both.

Answer 1

使用 ViewPager 时不可能。 ViewPager 根据您的滑动方向至少加载 one right/left adjacent 个片段 current 个片段。

如果你阅读ViewPager文档，有一个方法ViewPager.setOffscreenPageLimit(LIMIT)支持屏幕外页面限制，它的default值是1。

SetOffscreenPageLimit:

Set the number of pages that should be retained to either side of the current page in the view hierarchy in an idle state. Pages beyond this limit will be recreated from the adapter when needed.

This is offered as an optimization. If you know in advance the number of pages you will need to support or have lazy-loading mechanisms in place on your pages, tweaking this setting can have benefits in perceived smoothness of paging animations and interaction. If you have a small number of pages (3-4) that you can keep active all at once, less time will be spent in layout for newly created view subtrees as the user pages back and forth.

You should keep this limit low, especially if your pages have complex layouts. This setting defaults to 1.

参见 documentation。

以下是一些相关的回答：

1. ViewPager.setOffscreenPageLimit(0) doesn't work as expected

2. How can make my ViewPager load only one page at a time ie setOffscreenPageLimit(0);

3. How does setOffscreenPageLimit() improve ViewPager performance by retaining more offscreen Fragments?

Answer 2

its Default behavior of ViewPager if you are in A then it loads B also and when your reach B it will Load C and A also is Loaded now when to reach at C its destroy the View of A and now when you come again to B it will Load A again, in a simple way ViewPager Maintain the One Next and One previous state of View by Default.

要克服这个问题，您应该使用 ViewPager.setOffscreenPageLimit(number) 这里的数字是为下一个和上一个视图模拟加载的页面数。

Answer 3

我只有 3 个选项卡，设置ViewPager.setOffscreenPageLimit(2)对我有用。

尝试ViewPager.setOffscreenPageLimit(totTabs - 1)

带有 ViewPager 的 TabLayout 未按预期工作

TabLayout with ViewPager not working as expected

android

android-viewpager

android-tablayout