在 Fragment 类中创建 Activity

Question

我的 MainActivity 的 Fragment 内部类中有一个名为 PinnedSectionListActivity 的内部类。我想在我的片段类中创建这个 PinnedSectionActivity 的实例。这样当我的片段类被实例化时，它将返回创建的那个 ListActivity 的实例。继续尝试，但无济于事。提前致谢。

这是我的 MainActivity。

package com.example.android.navigationdrawerexample;

import java.util.Locale;

import com.hb.views.PinnedSectionListView;
import com.hb.views.PinnedSectionListView.PinnedSectionListAdapter;
import android.annotation.SuppressLint;
import android.app.Activity;
import android.app.Fragment;
import android.app.FragmentManager;
import android.app.ListActivity;
import android.app.SearchManager;
import android.content.Context;
import android.content.Intent;
import android.content.res.Configuration;
import android.graphics.Color;
import android.os.Build;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.view.GravityCompat;
import android.support.v4.widget.DrawerLayout;
import android.view.LayoutInflater;
import android.view.Menu;
import android.view.MenuInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.SectionIndexer;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
    private DrawerLayout mDrawerLayout;
    private ListView mDrawerList;
    private ActionBarDrawerToggle mDrawerToggle;

    private CharSequence mDrawerTitle;
    private CharSequence mTitle;
    private String[] mPlanetTitles;

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

        mTitle = mDrawerTitle = getTitle();
        mPlanetTitles = getResources().getStringArray(R.array.planets_array);
        mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
        mDrawerList = (ListView) findViewById(R.id.left_drawer);

        // set a custom shadow that overlays the main content when the drawer opens
        mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow, GravityCompat.START);

        // set up the drawer's list view with items and click listener
        mDrawerList.setAdapter(new ArrayAdapter<String>(this,R.layout.drawer_list_item, mPlanetTitles));
        //mDrawerList.setAdapter(new ArrayAdapter<String>(this,R.layout.drawer_list_item, mPlanetTitles));

        mDrawerList.setOnItemClickListener(new DrawerItemClickListener());

        // enable ActionBar app icon to behave as action to toggle nav drawer
        getActionBar().setDisplayHomeAsUpEnabled(true);
        getActionBar().setHomeButtonEnabled(true);

        // ActionBarDrawerToggle ties together the the proper interactions
        // between the sliding drawer and the action bar app icon
        mDrawerToggle = new ActionBarDrawerToggle(
                this,                  /* host Activity */
                mDrawerLayout,         /* DrawerLayout object */
                R.drawable.ic_drawer,  /* nav drawer image to replace 'Up' caret */
                R.string.drawer_open,  /* "open drawer" description for accessibility */
                R.string.drawer_close  /* "close drawer" description for accessibility */
                ) {
            public void onDrawerClosed(View view) {
                getActionBar().setTitle(mTitle);
                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
            }

            public void onDrawerOpened(View drawerView) {
                getActionBar().setTitle(mDrawerTitle);
                invalidateOptionsMenu(); // creates call to onPrepareOptionsMenu()
            }
        };
        mDrawerLayout.setDrawerListener(mDrawerToggle);

        if (savedInstanceState == null) {
            selectItem(0);
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        MenuInflater inflater = getMenuInflater();
        inflater.inflate(R.menu.main, menu);
        return super.onCreateOptionsMenu(menu);
    }

    /* Called whenever we call invalidateOptionsMenu() */
    @Override
    public boolean onPrepareOptionsMenu(Menu menu) {
        // If the nav drawer is open, hide action items related to the content view
        boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
        menu.findItem(R.id.action_websearch).setVisible(!drawerOpen);
        return super.onPrepareOptionsMenu(menu);
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item) {
         // The action bar home/up action should open or close the drawer.
         // ActionBarDrawerToggle will take care of this.
        if (mDrawerToggle.onOptionsItemSelected(item)) {
            return true;
        }
        // Handle action buttons
        switch(item.getItemId()) {
        case R.id.action_websearch:
            // create intent to perform web search for this planet
            Intent intent = new Intent(Intent.ACTION_WEB_SEARCH);
            intent.putExtra(SearchManager.QUERY, getActionBar().getTitle());
            // catch event that there's no activity to handle intent
            if (intent.resolveActivity(getPackageManager()) != null) {
                startActivity(intent);
            } else {
                Toast.makeText(this, R.string.app_not_available, Toast.LENGTH_LONG).show();
            }
            return true;
        default:
            return super.onOptionsItemSelected(item);
        }
    }

    /* The click listner for ListView in the navigation drawer */
    private class DrawerItemClickListener implements ListView.OnItemClickListener {
        @Override
        public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
            selectItem(position);
        }
    }

    private void selectItem(int position) {
        // update the main content by replacing fragments
        Fragment fragment = new PlanetFragment();
        Bundle args = new Bundle();
        args.putInt(PlanetFragment.ARG_PLANET_NUMBER, position);
        fragment.setArguments(args);

        FragmentManager fragmentManager = getFragmentManager();
        fragmentManager.beginTransaction().replace(R.id.content_frame, fragment).commit();

        // update selected item and title, then close the drawer
        mDrawerList.setItemChecked(position, true);
        setTitle(mPlanetTitles[position]);
        mDrawerLayout.closeDrawer(mDrawerList);
    }

    @Override
    public void setTitle(CharSequence title) {
        mTitle = title;
        getActionBar().setTitle(mTitle);
    }

    /**
     * When using the ActionBarDrawerToggle, you must call it during
     * onPostCreate() and onConfigurationChanged()...
     */

    @Override
    protected void onPostCreate(Bundle savedInstanceState) {
        super.onPostCreate(savedInstanceState);
        // Sync the toggle state after onRestoreInstanceState has occurred.
        mDrawerToggle.syncState();
    }

    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        // Pass any configuration change to the drawer toggls
        mDrawerToggle.onConfigurationChanged(newConfig);
    }

    /**
     * Fragment that appears in the "content_frame", shows a planet
     */
    public static class PlanetFragment extends Fragment {
        public static final String ARG_PLANET_NUMBER = "planet_number";

        public PlanetFragment() {
            // Empty constructor required for fragment subclasses
        }

        /**
         * 
         * 
         * 
         * I WOULD LIKE TO CREATE THE PINNEDSECTION ACTIVITY
         * WHEN THE FRAGMENT GETS INITIALIZED. WOULD I HAVE TO CREATE
         * 
         * 
         * 
         * 
         */
        @Override
        public View onCreateView(LayoutInflater inflater, ViewGroup container,
                Bundle savedInstanceState) {
            View rootView = inflater.inflate(R.layout.fragment_planet, container, false);
            int i = getArguments().getInt(ARG_PLANET_NUMBER);
            String planet = getResources().getStringArray(R.array.planets_array)[i];

            int imageId = getResources().getIdentifier(planet.toLowerCase(Locale.getDefault()),
                            "drawable", getActivity().getPackageName());
            ((ImageView) rootView.findViewById(R.id.image)).setImageResource(imageId);
            getActivity().setTitle(planet);
            return rootView;
        }
    }

    /**
     * 
     * @author randolphgordon
     *
     */
    public class PinnedSectionListActivity extends ListActivity implements OnClickListener {

        class SimpleAdapter extends ArrayAdapter<Item> implements PinnedSectionListAdapter {

            private final int[] COLORS = new int[] {
                R.color.green_light, 
                R.color.orange_light,
                R.color.blue_light, 
                R.color.red_light };

            public SimpleAdapter(Context context, int resource, int textViewResourceId) {
                super(context, resource, textViewResourceId);

                //final int sectionsNumber = 'Z' - 'A' + 1;
                final int sectionsNumber = 'Z' - 'A' + 1;

                prepareSections(sectionsNumber);

                int sectionPosition = 0, listPosition = 0;

                for (int i=0; i< sectionsNumber; i++) {

                    String title = null;

                    final String []country = {
                            "Korean", "Japanese", "Chinese", "Cambodian", "Loas", "Taiwamese"
                    };


                    final String [] CATEGORY = {
                        "Language",
                        "sports",
                        "love",
                        "luxury",
                        "vacation",
                        "games",
                        "home",
                        "travel",
                        "electronics",
                        "movies",
                    };

                    switch (('A' + i)) {
                    case ('A' + 0):
                        title = country[0];
                        break;
                    case ('A' + 1):
                        title = country[1];
                        break;
                    case ('A' + 2):
                        title = country[2];
                        break;
                    case ('A' + 3):
                        title = country[3];
                        break;
                    case ('A' + 4):
                        title = country[4];
                        break;
                    case ('A' + 5):
                        title = country[5];
                        break;
                    default:
                        break;
                    }

                    //Create a new Item class with section header and Name
                    Item section = new Item(Item.SECTION, title + " " + i);
                    //Item section = new Item(Item.SECTION, String.valueOf((char)('A' + i)));

                    section.sectionPosition = sectionPosition;
                    section.listPosition = listPosition++;
                    onSectionAdded(section, sectionPosition);
                    add(section);

                    final int itemsNumber = CATEGORY.length; 

                    //(int) Math.abs((Math.cos(2f*Math.PI/3f * sectionsNumber / (i+1f)) * 25f));

                    // For loop to iterate the exact number of itemNumber
                    for (int j = 0;j < CATEGORY.length;j++) {
                        //Item item = new Item(Item.ITEM, section.text.toUpperCase(Locale.KOREA) + " - " + j);
                        Item item = new Item(Item.ITEM, CATEGORY[j]);
                        item.sectionPosition = sectionPosition;
                        item.listPosition = listPosition++;
                        add(item);
                    }

                    sectionPosition++;
                }
            }

            protected void prepareSections(int sectionsNumber) { }
            protected void onSectionAdded(Item section, int sectionPosition) { }

            @Override public View getView(int position, View convertView, ViewGroup parent) {
                TextView view = (TextView) super.getView(position, convertView, parent);
                view.setTextColor(Color.DKGRAY );
                view.setTag("" + position);
                Item item = getItem(position);
                if (item.type == Item.SECTION) {
                    //view.setOnClickListener(PinnedSectionListActivity.this);
                    view.setBackgroundColor(parent.getResources().getColor(COLORS[item.sectionPosition % COLORS.length]));
                }
                return view;
            }

            @Override public int getViewTypeCount() {
                return 2;
            }

            @Override public int getItemViewType(int position) {
                return getItem(position).type;
            }

            @Override
            public boolean isItemViewTypePinned(int viewType) {
                return viewType == Item.SECTION;
            }

        }

        class Item {

            public static final int ITEM = 0;
            public static final int SECTION = 1;

            public final int type;
            public final String text;

            public int sectionPosition;
            public int listPosition;

            public Item(int type, String text) {
                this.type = type;
                this.text = text;
            }

            @Override public String toString() {
                return text;
            }

        }



        class FastScrollAdapter extends SimpleAdapter implements SectionIndexer {

            private Item[] sections;

            public FastScrollAdapter(Context context, int resource, int textViewResourceId) {
                super(context, resource, textViewResourceId);
            }

            @Override protected void prepareSections(int sectionsNumber) {
                sections = new Item[sectionsNumber];
            }

            @Override protected void onSectionAdded(Item section, int sectionPosition) {
                sections[sectionPosition] = section;
            }

            @Override public Item[] getSections() {
                return sections;
            }

            @Override public int getPositionForSection(int section) {
                if (section >= sections.length) {
                    section = sections.length - 1;
                }
                return sections[section].listPosition;
            }

            @Override public int getSectionForPosition(int position) {
                if (position >= getCount()) {
                    position = getCount() - 1;
                }
                return getItem(position).sectionPosition;
            }

        }




        private boolean hasHeaderAndFooter;
        private boolean isFastScroll;
        private boolean addPadding;
        private boolean isShadowVisible = true;

        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);
            if (savedInstanceState != null) {
                isFastScroll = savedInstanceState.getBoolean("isFastScroll");
                addPadding = savedInstanceState.getBoolean("addPadding");
                isShadowVisible = savedInstanceState.getBoolean("isShadowVisible");
                hasHeaderAndFooter = savedInstanceState.getBoolean("hasHeaderAndFooter");
            }
            initializeHeaderAndFooter();
            initializeAdapter();
            initializePadding();
        }

        @Override
        protected void onSaveInstanceState(Bundle outState) {
            super.onSaveInstanceState(outState);
            outState.putBoolean("isFastScroll", isFastScroll);
            outState.putBoolean("addPadding", addPadding);
            outState.putBoolean("isShadowVisible", isShadowVisible);
            outState.putBoolean("hasHeaderAndFooter", hasHeaderAndFooter);
        }

        @Override
        protected void onListItemClick(ListView l, View v, int position, long id) {
            Item item = (Item) getListView().getAdapter().getItem(position);
            if (item != null) {
                Toast.makeText(this, "Item " + position + ": " + item.text, Toast.LENGTH_SHORT).show();
            } else {
                Toast.makeText(this, "Item " + position, Toast.LENGTH_SHORT).show();
            }
        }

        @Override
        public boolean onCreateOptionsMenu(Menu menu) {
            getMenuInflater().inflate(R.menu.main, menu);
            menu.getItem(0).setChecked(isFastScroll);
            menu.getItem(1).setChecked(addPadding);
            menu.getItem(2).setChecked(isShadowVisible);
            return true;
        }

        @Override
        public boolean onOptionsItemSelected(MenuItem item) {
            switch (item.getItemId()) {
                case R.id.action_fastscroll:
                    isFastScroll = !isFastScroll;
                    item.setChecked(isFastScroll);
                    initializeAdapter();
                    break;
                case R.id.action_addpadding:
                    addPadding = !addPadding;
                    item.setChecked(addPadding);
                    initializePadding();
                    break;
                case R.id.action_showShadow:
                    isShadowVisible = !isShadowVisible;
                    item.setChecked(isShadowVisible);
                    ((PinnedSectionListView)getListView()).setShadowVisible(isShadowVisible);
                    break;
                case R.id.action_showHeaderAndFooter:
                    hasHeaderAndFooter = !hasHeaderAndFooter;
                    item.setChecked(hasHeaderAndFooter);
                    initializeHeaderAndFooter();
                    break;
            }
            return true;
        }

        private void initializePadding() {
            float density = getResources().getDisplayMetrics().density;
            int padding = addPadding ? (int) (16 * density) : 0;
            getListView().setPadding(padding, padding, padding, padding);
        }

        private void initializeHeaderAndFooter() {
            setListAdapter(null);
            if (hasHeaderAndFooter) {
                ListView list = getListView();

                LayoutInflater inflater = LayoutInflater.from(this);
                TextView header1 = (TextView) inflater.inflate(android.R.layout.simple_list_item_1, list, false);
                header1.setText("First header");
                list.addHeaderView(header1);

                TextView header2 = (TextView) inflater.inflate(android.R.layout.simple_list_item_1, list, false);
                header2.setText("Second header");
                list.addHeaderView(header2);

                TextView footer = (TextView) inflater.inflate(android.R.layout.simple_list_item_1, list, false);
                footer.setText("Single footer");
                list.addFooterView(footer);
            }
            initializeAdapter();
        }

        @SuppressLint("NewApi")
        private void initializeAdapter() {
            getListView().setFastScrollEnabled(isFastScroll);
            if (isFastScroll) {
                if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.HONEYCOMB) {
                    getListView().setFastScrollAlwaysVisible(true);
                }
                setListAdapter(new FastScrollAdapter(this, android.R.layout.simple_list_item_1, android.R.id.text1));
            } else {
                setListAdapter(new SimpleAdapter(this, android.R.layout.simple_list_item_1, android.R.id.text1));
            }
        }

        @Override
        public void onClick(View v) {
            Toast.makeText(this, "Item: " + v.getTag() , Toast.LENGTH_SHORT).show();
        }

    }

}

Answer 1

如果您正在谈论从片段启动活动，请考虑更多地使用显式 Intent http://developer.android.com/reference/android/content/Intent.html

如果您想在 Fragment 中托管由 Activity 呈现的视图，那么您说的是异端 =] Fragment 应该处理 Activity 的 Fragments；活动是用户当时正在执行的功能的演示者。例如您的 gmail 收件箱是一项活动，那些滑动的消息列表和邮件阅读窗口是活动中的片段。

这里有一条经验法则：如果您可以从一个活动传递到下一个活动，那么您应该能够以最少的序列化来做到这一点；如果你想管理几种查看大用户状态的方法，那么你就在一个活动中，处理片段。

单身丧命。

gl hf!

Answer 2

我认为将活动实例存储在片段中并不是一个好主意。它可能很容易导致内存泄漏 - 您不应该将 Context 存储在其外部，因为您可能会泄漏它。

无论如何，您始终可以通过调用Fragment 类的getActivity() 方法来获取当前与片段关联的活动。

另外，不要将活动创建为片段的内部类。最好将它们作为单独的类保存，每个类都在自己的文件中。