如何扩展一个普通的Java类Android？

Question

I am having problems properly setting up a complex listview: I am trying to create a two-level listview with a swipe tab layout, but my second level does not react to any actions taking place (eg clicking on an item in the list).

Perhaps I need to extend a plain java file class but I am unsure how to do this. Suggestions?

File MainActivity.Java

  package com.learn2crack.tab;

import android.app.ActionBar;
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.view.ViewPager;

public class MainActivity extends FragmentActivity implements AnItemClickListener, HeadlinesFragment.OnHeadlineSelectedListener {
    ViewPager Tab;
    TabPagerAdapter TabAdapter;
    ActionBar actionBar;

    public void clickHappens(int position){
        //whatever you need to do in response to a click knowing what position in the 
        //data set correlated to the row that was clicked.
         // The user selected the headline of an article from the HeadlinesFragment

        // Capture the article fragment from the activity layout
        ArticleFragment articleFrag = (ArticleFragment)
                getSupportFragmentManager().findFragmentById(R.id.article_fragment);

        if (articleFrag != null) {
            // If article frag is available, we're in two-pane layout...

            // Call a method in the ArticleFragment to update its content
            articleFrag.updateArticleView(position);

        } else {
            // If the frag is not available, we're in the one-pane layout and must swap frags...

            // Create fragment and give it an argument for the selected article
            ArticleFragment newFragment = new ArticleFragment();
            Bundle args = new Bundle();
            args.putInt(ArticleFragment.ARG_POSITION, position);
            newFragment.setArguments(args);
            android.support.v4.app.FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

            // Replace whatever is in the fragment_container view with this fragment,
            // and add the transaction to the back stack so the user can navigate back
            transaction.replace(R.id.fragment_container, newFragment);
            transaction.addToBackStack(null);

            // Commit the transaction
            transaction.commit();

        }

    }

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        TabAdapter = new TabPagerAdapter(getSupportFragmentManager());

        Tab = (ViewPager)findViewById(R.id.pager);
        Tab.setOnPageChangeListener(
                new ViewPager.SimpleOnPageChangeListener() {
                    @Override
                    public void onPageSelected(int position) {

                        actionBar = getActionBar();
                        actionBar.setSelectedNavigationItem(position);                    }
                });
        Tab.setAdapter(TabAdapter);

        actionBar = getActionBar();
        //Enable Tabs on Action Bar
        actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
        ActionBar.TabListener tabListener = new ActionBar.TabListener(){

            @Override
            public void onTabReselected(android.app.ActionBar.Tab tab,
                    FragmentTransaction ft) {
                // TODO Auto-generated method stub

            }

            @Override
             public void onTabSelected(ActionBar.Tab tab, FragmentTransaction ft) {

                Tab.setCurrentItem(tab.getPosition());
            }

            @Override
            public void onTabUnselected(android.app.ActionBar.Tab tab,
                    FragmentTransaction ft) {
                // TODO Auto-generated method stub

            }};
            //Add New Tab
            actionBar.addTab(actionBar.newTab().setText("Software Search").setTabListener(tabListener));
            actionBar.addTab(actionBar.newTab().setText("Maps").setTabListener(tabListener));
            actionBar.addTab(actionBar.newTab().setText("Scanner").setTabListener(tabListener));

    }

@Override
public void onArticleSelected(int position) {
    // TODO Auto-generated method stub

}


}

File SoftWareSearchActivity.java

package com.learn2crack.tab;

import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTransaction;

interface OnHeadlineSelectedListener {
    /** Called by HeadlinesFragment when a list item is selected */
    public void onArticleSelected(int position);
}

public class SoftWareSearchActivity extends FragmentActivity 
        implements HeadlinesFragment.OnHeadlineSelectedListener {

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.news_articles);

        // Check whether the activity is using the layout version with
        // the fragment_container FrameLayout. If so, we must add the first fragment
        if (findViewById(R.id.fragment_container) != null) {

            // However, if we're being restored from a previous state,
            // then we don't need to do anything and should return or else
            // we could end up with overlapping fragments.
            if (savedInstanceState != null) {
                return;
            }

            // Create an instance of ExampleFragment
            HeadlinesFragment firstFragment = new HeadlinesFragment();

            // In case this activity was started with special instructions from an Intent,
            // pass the Intent's extras to the fragment as arguments
            firstFragment.setArguments(getIntent().getExtras());

            // Add the fragment to the 'fragment_container' FrameLayout
            getSupportFragmentManager().beginTransaction()
                    .add(R.id.fragment_container, firstFragment).commit();
        }
    }

    public void onArticleSelected(int position) {
        // The user selected the headline of an article from the HeadlinesFragment

        // Capture the article fragment from the activity layout
        ArticleFragment articleFrag = (ArticleFragment)
                getSupportFragmentManager().findFragmentById(R.id.article_fragment);

        if (articleFrag != null) {
            // If article frag is available, we're in two-pane layout...

            // Call a method in the ArticleFragment to update its content
            articleFrag.updateArticleView(position);

        } else {
            // If the frag is not available, we're in the one-pane layout and must swap frags...

            // Create fragment and give it an argument for the selected article
            ArticleFragment newFragment = new ArticleFragment();
            Bundle args = new Bundle();
            args.putInt(ArticleFragment.ARG_POSITION, position);
            newFragment.setArguments(args);
            FragmentTransaction transaction = getSupportFragmentManager().beginTransaction();

            // Replace whatever is in the fragment_container view with this fragment,
            // and add the transaction to the back stack so the user can navigate back
            transaction.replace(R.id.fragment_container, newFragment);
            transaction.addToBackStack(null);

            // Commit the transaction
            transaction.commit();
        }
    }
}

File HeadlinesFragment.java

package com.learn2crack.tab;

import android.app.Activity;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.ListFragment;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.ListView;

public class HeadlinesFragment extends ListFragment {
    OnHeadlineSelectedListener mCallback;


    // The container Activity must implement this interface so the frag can deliver messages
    public interface OnHeadlineSelectedListener {
        /** Called by HeadlinesFragment when a list item is selected */
        public void onArticleSelected(int position);
    }

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

        // We need to use a different list item layout for devices older than Honeycomb
        int layout = Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB ?
                android.R.layout.simple_list_item_activated_1 : android.R.layout.simple_list_item_1;

        // Create an array adapter for the list view, using the Ipsum headlines array
        setListAdapter(new ArrayAdapter<String>(getActivity(), layout, Ipsum.Headlines));
    }

    @Override
    public void onStart() {
        super.onStart();

        // When in two-pane layout, set the listview to highlight the selected list item
        // (We do this during onStart because at the point the listview is available.)
        if (getFragmentManager().findFragmentById(R.id.article_fragment) != null) {
            getListView().setChoiceMode(ListView.CHOICE_MODE_SINGLE);
        }
    }

    @Override
    public void onAttach(Activity activity) {
        super.onAttach(activity);

        // This makes sure that the container activity has implemented
        // the callback interface. If not, it throws an exception.
        try {
            mCallback = (OnHeadlineSelectedListener) activity;
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString()
                    + " must implement OnHeadlineSelectedListener");
        }
    }

    @Override
    public void onListItemClick(ListView l, View v, int position, long id) {
        // Notify the parent activity of selected item
        mCallback.onArticleSelected(position);

        // Set the item as checked to be highlighted when in two-pane layout
        getListView().setItemChecked(position, true);
    }
}

File ArticleFragment.java

package com.learn2crack.tab;

import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;

public class ArticleFragment extends Fragment {
    final static String ARG_POSITION = "position";
    int mCurrentPosition = -1;

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, 
        Bundle savedInstanceState) {

        // If activity recreated (such as from screen rotate), restore
        // the previous article selection set by onSaveInstanceState().
        // This is primarily necessary when in the two-pane layout.
        if (savedInstanceState != null) {
            mCurrentPosition = savedInstanceState.getInt(ARG_POSITION);
        }

        // Inflate the layout for this fragment
        return inflater.inflate(R.layout.article_view, container, false);
    }

    @Override
    public void onStart() {
        super.onStart();

        // During startup, check if there are arguments passed to the fragment.
        // onStart is a good place to do this because the layout has already been
        // applied to the fragment at this point so we can safely call the method
        // below that sets the article text.
        Bundle args = getArguments();
        if (args != null) {
            // Set article based on argument passed in
            updateArticleView(args.getInt(ARG_POSITION));
        } else if (mCurrentPosition != -1) {
            // Set article based on saved instance state defined during onCreateView
            updateArticleView(mCurrentPosition);
        }
    }

    public void updateArticleView(int position) {
        TextView article = (TextView) getActivity().findViewById(R.id.article);
        article.setText(Ipsum.Articles[position]);
        mCurrentPosition = position;
    }

    @Override
    public void onSaveInstanceState(Bundle outState) {
        super.onSaveInstanceState(outState);

        // Save the current article selection in case we need to recreate the fragment
        outState.putInt(ARG_POSITION, mCurrentPosition);
    }
}

File AnItemClickListener.java

package com.learn2crack.tab;

public interface AnItemClickListener {

    void clickHappens(int i);

}

Answer 1

short answer: you don't, classes are classes b/c you said 'class' at the beginning of the class; they are outer classes if they are outer and match the file name

if you want to communicate between a fragment and the activity that is holding it, first write an interface; u can get away with not writing one, but it's good form and helps organize your code:

package com.yourcompany.appname.interfaces;

public interface AnItemClickListener
{
void clickHappens(int i);
}

note the lack of a method body, also note that since I'm calling this an interface, I don't need to specify that these are abstract, but they are. You can add more methods, and any class that implements this must have a clickHappens method or itself be abstract, containing classes that do.

Then you edit the top of your mainActivity to say: 'public class MainActivity extends FragmentActivity implements AnItemClickListener, HeadlinesFragment.OnHeadlineSelectedListener {', meaning it has methods that provide the body for all the abstract methods in both the AnItemClickListener and the HeadlinesFragment.OnHeadlineSelectedListener interfaces. At this point you IDE should be throwing an error and telling you that you need to implement an abstract function, so put the following method in this class:

public void clickHappens(int position){
    //whatever you need to do in response to a click knowing what position in the 
    //data set correlated to the row that was clicked.
}

isn't that neat-o?

now, you can call this function in one of two ways that come immediatly to mind: if we know the fragment is only ever going to be running as a part of this activity( not being reused, which defeats one of the purposes for Fragments ) then in our fragment we can say

MainActivity.this.clickHappens(pos); //where pos is the position

but this isn't using the interface.

more robustly, since we pass this to the Fragment during onAttach, we make sure a callback can be cast correctly in onAttach like so:

class aFragment extends ListFragment{
Activity callback;

@Override
onAttach{
    try {
            callback = (AnItemClickListener) activity; //look familiar?
        } catch (ClassCastException e) {
            throw new ClassCastException(activity.toString() + 
                                     " must implement AnItemClickListener");
        }
    }
}

so when you override onListItemClick, just say

callback.clickHappens( position );

and you've sent the clicked position to the activity that passed 'this' to the Fragment.

tell me if any part of that isn't clear =]

a more "normal" use of interfaces is when you do something like

Map map = new Hashmap<String, String>;

and then

map.get(s);

in that case, though map is a Map, you aren't calling .get() of Map--Map is only the base class--you are calling the method .get of HashMap.

gl hf