从Activity调用Tabbed Fragment方法

Question

I have one activity that comprises of three fragments. The fragments use the actionbar tabs using a PagerAdapter. What I want to do is access a method in the active tabbed fragment from the main activity. I have tried the below code but this just returns the fragment as null, so I guess it cant find it within the tabs!

 NPListFragment articleFrag = (NPListFragment) getSupportFragmentManager().findFragmentByTag("NP");
    articleFrag.refreshT();

PagerAdapter:

public class AppSectionsPagerAdapter extends FragmentPagerAdapter {
public AppSectionsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int i) {
    switch (i) {
        case 0:
            return new NPListFragment();
        case 1:
            return new PListFragment();
        case 2:
            return new FavouritesFragment();
    }
    return null;
}

@Override
public int getCount() {
    return 3;
}

} Can anyone advise? I have spent about 6 hours on this, i'm just not making any progress resolving this.

Answer 1

What you should do is : create only once each fragment and then give it for all calls to the getItem method.

For instance :

public class AppSectionsPagerAdapter extends FragmentPagerAdapter {

Fragment one, two, three;

public AppSectionsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int i) {
    switch (i) {
        case 0:
            if(one == null)
                one = new NPListFragment();
            return one;
        case 1:
            if(two == null)
                two= new PListFragment();
            return two;
        case 2:
            if(three == null)
                three= new FavouritesFragment();
            return three;
    }
    return null;
}

@Override
public int getCount() {
    return 3;
}

} 

Now, even you in your activity you can call getItem

You'll just need to cast it to the real fragment class if you want to call a specific method.

int pos = viewpager.getCurrentItem();    
Fragment activeFragment = adapter.getItem(pos);
if(pos == 0)
    ((NPListFragment)activeFragment).refreshT();
...

Answer 2

You need to register your fragments while populating, then access them from outside.

public class AppSectionsPagerAdapter extends FragmentPagerAdapter {
private SparseArray<Fragment> registeredFragments = new SparseArray<>();
public AppSectionsPagerAdapter(FragmentManager fm) {
    super(fm);
}

@Override
public Fragment getItem(int i) {
    switch (i) {
        case 0:
            return new NPListFragment();
        case 1:
            return new PListFragment();
        case 2:
            return new FavouritesFragment();
    }
    return null;
}

@Override
public int getCount() {
    return 3;
}

@Override
public Object instantiateItem(ViewGroup container, int position) {
    Fragment fragment = (Fragment) super.instantiateItem(container, position);
    registeredFragments.put(position, fragment);
    return fragment;
}

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

public Fragment getRegisteredFragment(int position) {
    return registeredFragments.get(position);
}

Now you can get registeredFragments from outside

int pos = viewpager.getCurrentItem();
Fragment fragment = adapter.getRegisteredFragment(pos);
switch (pos) {
    case 0: {
        ((NPListFragment) fragment).refreshT();
        break;
    }
    case 1: {
        ((PListFragment) fragment).refreshK();
        break;
    }
    case 2: {
        ((FavouritesFragment) fragment).refreshL();
        break;
    }
}

Answer 3

I solved this problem.

It is happening because Adapter is initializing every time a new Fragment when get item is called.

To solve this you need to make a array of Required Fragment in onCreate method

Fragment[] FragmentArray;
FragmentArray = new Fragment[] {new Fragment 1,new Fragment 2...};   // all fragment goes in array
...

get item(int position)
...
return FragmentArray[position]
...
Fragment1 f= (Fragment1) FragmentArray[0];
f.refresh()  // call required function

Answer 4

I use the fragment manager to get the fragment. My fragments are initialised in view pager like below in ViewPagerAdapter.class -

@Override
    public Fragment getItem(int i) {
        Fragment fragment = null;
        switch (i) {
            case 0:
                fragment = Fragment.instantiate(mContext, Fragment1.class.getName());
                break;
            case 1:
                fragment = Fragment.instantiate(mContext, Fragment2.class.getName());
                break;
            case 2:
                fragment = Fragment.instantiate(mContext, Fragment3.class.getName());
                break;
        }
        return fragment;
    }

Then in MainActivity -

List<Fragment> fragments = getSupportFragmentManager().getFragments();
        if (fragments != null) {
            for (Fragment fragment : fragments) {
                if (fragment instanceof Fragment1) {
                    ((Fragment1) fragment).fragmentOne();
                    break;
                }
            }
        }