android - ViewPager - 从 setOnTabSelectedListener 启动 Activity

Question

我试图在选择特定选项卡时启动一个 Activity ，但当我从该 Activity 返回时，我希望显示前一个选项卡而不是我单击的选项卡。就像您在 Instagram 上点击加号按钮一样。

像这样:

• 默认 fragment 1/标签 1

• 转到 fragment 5/Tab 5

• 点击tab 3，弹出 Activity

• 返回，查看 Fragment 5/Tab 5

现在，我将上次访问的选项卡索引存储在一个变量中，然后当单击选项卡 3 时，它只会转到上次访问的选项卡。

tabLayout.setOnTabSelectedListener(
            new TabLayout.ViewPagerOnTabSelectedListener(viewPager) {
                @Override
                public void onTabSelected(TabLayout.Tab tab) {
                  //super.onTabSelected(tab); -- Should keep this or leave it commented out? 
                    int pos = tab.getPosition();
                    switch (pos) {
                        case 0:
                            viewPager.setCurrentItem(tab.getPosition(), false);
                            getSupportActionBar().setTitle("Home");
                            pre_pos = pos;
                            pre_title = "Home";
                            break;
                        case 1:
                            viewPager.setCurrentItem(tab.getPosition(), false);
                            getSupportActionBar().setTitle("Trending");
                            pre_pos = pos;
                            pre_title = "Trending";
                            break;
                        case 2:
                            viewPager.setCurrentItem(pre_pos, false);
                            getSupportActionBar().setTitle(pre_title);

                            Intent intent = new Intent(MainActivity.this, NewEvent_Activity.class);
                            startActivity(intent);
                            Toast.makeText(getApplicationContext(), 
                                    "Curr: "+ viewPager.getCurrentItem()+
                                    " Prev: " + pre_pos +
                                    " Clicked: " +tab.getPosition(), 
                                    Toast.LENGTH_SHORT).show();
                            break;
                        case 3:
                            viewPager.setCurrentItem(tab.getPosition(), false);
                            getSupportActionBar().setTitle("Notifications");
                            pre_pos = pos;
                            pre_title = "Notifications";
                            break;
                        case 4:
                            viewPager.setCurrentItem(tab.getPosition(), false);
                            getSupportActionBar().setTitle("Profile");
                            pre_pos = pos;
                            pre_title = "Profile";
                            break;
                    }
                }
            });

在 ViwPager.java 中，它在调用 setCurrentItem() 时调用此函数

void setCurrentItemInternal(int item, boolean smoothScroll, boolean always, int velocity) {
    if (mAdapter == null || mAdapter.getCount() <= 0) {
        setScrollingCacheEnabled(false);
        return;
    }
    //I think my problem lies in the following line (mCurItem == item)
    if (!always && mCurItem == item && mItems.size() != 0) {
        setScrollingCacheEnabled(false);
        return;
    }

    if (item < 0) {
        item = 0;
    } else if (item >= mAdapter.getCount()) {
        item = mAdapter.getCount() - 1;
    }
    final int pageLimit = mOffscreenPageLimit;
    if (item > (mCurItem + pageLimit) || item < (mCurItem - pageLimit)) {
        // We are doing a jump by more than one page.  To avoid
        // glitches, we want to keep all current pages in the view
        // until the scroll ends.
        for (int i = 0; i < mItems.size(); i++) {
            mItems.get(i).scrolling = true;
        }
    }
    final boolean dispatchSelected = mCurItem != item;

    if (mFirstLayout) {
        // We don't have any idea how big we are yet and shouldn't have any pages either.
        // Just set things up and let the pending layout handle things.
        mCurItem = item;
        if (dispatchSelected) {
            dispatchOnPageSelected(item);
        }
        requestLayout();
    } else {
        populate(item);
        scrollToItem(item, smoothScroll, velocity, dispatchSelected);
    }
}

我认为这是我的问题所在，但我无法对其进行编辑。有什么建议吗？

谢谢。

Answer 1

在 Activity 上实现 ViewPager.OnPageChangeListener。在 viewpager 上设置监听器

 view_pager.setOnPageChangeListener(this);

在 OnPageSelected() 方法中:

@Override
public void onPageSelected(int position) {
    if (position == 3) {
        startActivity(new Intent(this,activity.class));
    }
}

覆盖 Activity 的 onResume 方法并写入:

@Override
public void onResume() {
    super.onResume();
   view_pager.setCurrentItem(0);
}