在viewpager中使用backstack和back按钮

Question

我正在使用viewpager在片段之间滑动,并希望后退按钮导航到先前查看的片段而不是结束活动.对不起,如果这是这个问题的副本,但我没有找到答案非常有帮助.显然onBackPressed需要被覆盖,但我不知道如何获取并显示正确的片段.我假设我应该使用fragmentmanager的backstack,但getSupportFragmentManager().getBackStackEntryCount()总是返回0.我是否需要使用手动将片段添加到backstack FragmentTransaction.addToBackStack()？如果是这样,我会在适配器中添加它？

这是我活动的代码,

public class PagerActivity extends FragmentActivity {

ArrayList<Sale> sales;
MyAdapter mAdapter;
ViewPager mPager;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Intent it = getIntent();
    this.sales = (ArrayList<Sale>) it.getExtras().get("sales");
    int position = it.getExtras().getInt("position");

    ActionBar actionBar = getActionBar();
    actionBar.setDisplayHomeAsUpEnabled(true);

    setContentView(R.layout.fragment_pager);
    mAdapter = new MyAdapter(getSupportFragmentManager());
    mPager = (ViewPager) findViewById(R.id.pager);
    mPager.setAdapter(mAdapter);
    mPager.setCurrentItem(position);

}

public class MyAdapter extends FragmentPagerAdapter {
    public MyAdapter(FragmentManager fragmentManager) {
        super(fragmentManager);
    }

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

    @Override
    public void destroyItem(ViewGroup container, int position, Object object) {
        super.destroyItem(container, position, object);
    }

    @Override
    public Fragment getItem(int position) {
        SalesThumbFragment frag = new SalesThumbFragment();
        return frag.newInstance(sales.get(position));
    }
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    switch (item.getItemId()) {
    case android.R.id.home:
        finish();
        return true;
    }
    return super.onOptionsItemSelected(item);
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.sales_controller, menu);
    return true;
}

@Override
public void onBackPressed() {
  if(getSupportFragmentManager().getBackStackEntryCount() != 0) {
    getSupportFragmentManager().popBackStack();
  } else {

    super.onBackPressed();
  }
}


}

Answer 1

在新的设计支持库中,我使用它
我有相同的问题,我按照这一步

在viewpager中有3个片段的主要活动中,我创建堆栈,推送和弹出数据.

//private Stack<Integer> stackkk;  ==> As i get edit suggestion 
private Stack<Integer> stackkk = new Stack<>(); // Edited 
private ViewPager mPager;
private int tabPosition = 0;



    mTabLayout.setupWithViewPager(mPager);
    mPager.addOnPageChangeListener(new TabLayout.TabLayoutOnPageChangeListener(mTabLayout));
    mTabLayout.setOnTabSelectedListener(new TabLayout.OnTabSelectedListener() {
        @Override
        public void onTabSelected(TabLayout.Tab tab) {
            tabPosition = tab.getPosition();
            mPager.setCurrentItem(tab.getPosition());

            if (stackkk.empty())
                stackkk.push(0);

            if (stackkk.contains(tabPosition)) {
                stackkk.remove(stackkk.indexOf(tabPosition));
                stackkk.push(tabPosition);
            } else {
                stackkk.push(tabPosition);
            }
        }

        @Override
        public void onTabUnselected(TabLayout.Tab tab) {
            tabPositionUnselected = tab.getPosition();
        }

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

并且在onBackPressed活动中,

@Override
public void onBackPressed() {
    if (stackkk.size() > 1) {
        stackkk.pop();
        mPager.setCurrentItem(stackkk.lastElement());
    } else {
    }
}

Answer 2

mPager.getCurrentItem()如果您在每次用户导航到新片段后使用一个字段来跟踪上一页的索引，那么在该onBackPressed()方法中，您应该能够调用mPager.setCurrentItem(previousPage)

或者，如果用户只能按顺序分页，那么您根本不需要字段，您可以这样做mPager.setCurrentItem(mPager.getCurrentItem()-1)