如何擴展一個普通的Java類Android？

Question

我在正確設置復雜的列表視圖時遇到問題：我正在嘗試創建帶有滑動選項卡布局的兩級列表視圖，但是我的第二級列表不對正在執行的任何操作做出反應（例如，單擊列表中的項目）。

也許我需要擴展一個普通的Java文件類，但是我不確定如何做到這一點。 有什么建議嗎？

文件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

}


}

文件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();
        }
    }
}

文件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);
    }
}

文件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);
    }
}

文件AnItemClickListener.java

package com.learn2crack.tab;

public interface AnItemClickListener {

    void clickHappens(int i);

}

Answer 1

簡短的答案：您不是，班級是您在班級開始時說過的“班級”。 如果它們在外部並且與文件名匹配，則它們是外部類

如果要在片段和保存該片段的活動之間進行通信，請首先編寫一個接口； 您可以不用編寫一個代碼而擺脫困境，但這是一種很好的形式，可以幫助您組織代碼：

package com.yourcompany.appname.interfaces;

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

請注意缺少方法主體，還請注意，由於我將其稱為接口，因此無需指定它們是抽象的，但它們是抽象的。 您可以添加更多方法，並且實現此方法的任何類都必須具有clickHappens方法，或者該方法本身必須是抽象的，其中包含具有該功能的類。

然后，編輯mainActivity的頂部說：'公共類MainActivity擴展FragmentActivity實現AnItemClickListener，HeadlinesFragment.OnHeadlineSelectedListener {'，這意味着它具有為AnItemClickListener和HeadlinesFragment.OnHeadlineSelectedListener接口中的所有抽象方法提供主體的方法。 此時，IDE應該拋出一個錯誤並告訴您需要實現一個抽象函數，因此請將以下方法放在此類中：

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.
}

那不是很整潔嗎？

現在，您可以立即想到的兩種方式之一調用此函數：如果我們知道片段僅將作為該活動的一部分運行（不會被重用，這將破壞Fragments的目的之一）然后在我們的片段中我們可以說

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

但這沒有使用界面。

更強大的是，由於我們在onAttach期間將其傳遞給Fragment，因此我們確保可以在onAttach中正確地進行回調，如下所示：

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");
        }
    }
}

因此，當您覆蓋onListItemClick時，只需說

callback.clickHappens( position );

並且您已經將點擊位置發送給了將“ this”傳遞給Fragment的活動。

告訴我其中的任何部分是否不清楚=]

當您做類似的事情時，更“正常”使用接口

Map map = new Hashmap<String, String>;

接着

map.get(s);

在這種情況下，盡管map是Map，但是您沒有調用Map的.get（），而Map只是基類，而是調用了HashMap的.get方法。

gl hf