我正在尝试在我的应用程序中创建一个收藏列表，为此我使用了本教程：
http://androidopentutorials.com/android-sharedpreferences-tutorial-and-example/
但为了获得收藏，我使用 NavigationDrawer 而不是 ActionBar。
问题是当我在抽屉中选择收藏夹或主页时没有任何反应。
Logcat 只显示一个与我的问题无关的错误。
我哪里错了？
错误：
06-30 17:41:48.530 6971-6971/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.boom.kayakapp, PID: 6971
java.lang.NullPointerException: Attempt to invoke virtual method 'java.lang.Object android.widget.ImageView.getTag()' on a null object reference
at com.boom.kayakapp.activities.MainActivity$2.onItemLongClick(MainActivity.java:148)
at android.widget.AbsListView.showContextMenuForChild(AbsListView.java:3162)
at android.view.ViewGroup.showContextMenuForChild(ViewGroup.java:693)
at android.view.ViewGroup.showContextMenuForChild(ViewGroup.java:693)
at android.view.View.showContextMenu(View.java:4853)
at android.view.View.performLongClick(View.java:4822)
at android.widget.TextView.performLongClick(TextView.java:8684)
at android.view.View$CheckForLongPress.run(View.java:19840)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5257)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
--------- beginning of system
06-30 17:41:48.572 933-933/? E/EGL_emulation﹕ tid 933: eglCreateSyncKHR(1237): error 0x3004 (EGL_BAD_ATTRIBUTE)
06-30 17:41:50.823 1232-1274/system_process E/InputDispatcher﹕ channel '10153f49 com.boom.kayakapp/com.boom.kayakapp.activities.MainActivity (server)' ~ Channel is unrecoverably broken and will be disposed!
06-30 17:42:02.006 7546-7546/? E/memtrack﹕ Couldn't load memtrack module (No such file or directory)
06-30 17:42:02.006 7546-7546/? E/android.os.Debug﹕ failed to load memtrack module: -2
06-30 17:42:02.041 7546-7555/? E/art﹕ Thread attaching while runtime is shutting down: Binder_1
06-30 17:42:02.402 7560-7560/? E/memtrack﹕ Couldn't load memtrack module (No such file or directory)
06-30 17:42:02.402 7560-7560/? E/android.os.Debug﹕ failed to load memtrack module: -2
06-30 17:42:02.460 7560-7570/? E/art﹕ Thread attaching while runtime is shutting down: Binder_1
主要活动：
import android.app.ProgressDialog;
import android.content.Intent;
import android.content.res.Configuration;
import android.content.res.TypedArray;
import android.graphics.Color;
import android.graphics.drawable.ColorDrawable;
import android.os.Bundle;
import android.os.StrictMode;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.widget.DrawerLayout;
import android.support.v7.app.ActionBarActivity;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import com.android.volley.Response;
import com.android.volley.VolleyError;
import com.android.volley.VolleyLog;
import com.android.volley.toolbox.JsonArrayRequest;
import com.boom.kayakapp.R;
import com.boom.kayakapp.adapters.AirlinesAdapter;
import com.boom.kayakapp.adapters.NavDrawerListAdapter;
import com.boom.kayakapp.controllers.AppController;
import com.boom.kayakapp.fragment.AirlinesFragment;
import com.boom.kayakapp.fragment.FavoriteFragment;
import com.boom.kayakapp.fragment.HomeFragment;
import com.boom.kayakapp.model.Airlines;
import com.boom.kayakapp.model.NavDrawerItem;
import com.boom.kayakapp.util.SharedPreference;
import org.json.JSONArray;
import org.json.JSONException;
import org.json.JSONObject;
import java.util.ArrayList;
import java.util.List;
public class MainActivity extends ActionBarActivity {
private Fragment contentFragment;
AirlinesFragment airlinesFragment;
FavoriteFragment favoriteFragment;
// JSON Node names
public static final String TAG_NAME = "name";
public static final String TAG_PHONE = "phone";
public static final String TAG_SITE = "site";
public static final String TAG_LOGO = "logoURL";
public static final String TAG_CODE = "code";
// Log tag
private static final String TAG = MainActivity.class.getSimpleName();
// Airlines json url
private static final String url = "https://www.kayak.com/h/mobileapis/directory/airlines";
public ProgressDialog pDialog;
public List<Airlines> airlinesList = new ArrayList<Airlines>();
public ListView listView;
public AirlinesAdapter adapterAirlines;
SharedPreference sharedPreference;
// DrawerLayout
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
// nav drawer title
private CharSequence mDrawerTitle;
// used to store app title
private CharSequence mTitle;
// slide menu items
private String[] navMenuTitles;
private TypedArray navMenuIcons;
private ArrayList<NavDrawerItem> navDrawerItems;
private NavDrawerListAdapter adapterDrawer;
@Override
protected void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_list);
// SharedPrefs
sharedPreference = new SharedPreference();
StrictMode.ThreadPolicy policy = new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
// Json Array
listView = (ListView) findViewById(R.id.list);
adapterAirlines = new AirlinesAdapter(this, airlinesList);
listView.setAdapter(adapterAirlines);
pDialog = new ProgressDialog(this);
// Showing progress dialog before making http request
pDialog.setMessage("Loading...");
pDialog.show();
// Listview OnItemClickListener
listView.setOnItemClickListener(new AdapterView.OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
// getting values from selected ListItem
String name = ((TextView) view.findViewById(R.id.name))
.getText().toString();
String phone = ((TextView) view.findViewById(R.id.phone))
.getText().toString();
String site = ((TextView) view.findViewById(R.id.site))
.getText().toString();
String logoURL = String.valueOf(((ImageView) view.findViewById(R.id.logoURL)));
// Starting single contact activity
Intent in = new Intent(getApplicationContext(),
SingleContactActivity.class);
in.putExtra(TAG_NAME, name);
in.putExtra(TAG_PHONE, phone);
in.putExtra(TAG_SITE, site);
in.putExtra(TAG_LOGO, logoURL);
startActivity(in);
}
});
listView.setOnItemLongClickListener(new AdapterView.OnItemLongClickListener() {
@Override
public boolean onItemLongClick(AdapterView<?> parent, View view,
int position, long id) {
ImageView button = (ImageView) view.findViewById(R.id.favorite_button);
String tag = button.getTag().toString();
if (tag.equalsIgnoreCase("grey")) {
sharedPreference.addFavorite(MainActivity.this, airlinesList.get(position));
Toast.makeText(MainActivity.this,
MainActivity.this.getResources().getString(R.string.add_favr),
Toast.LENGTH_SHORT).show();
button.setTag("red");
button.setImageResource(R.drawable.heart_red);
} else {
sharedPreference.removeFavorite(MainActivity.this, airlinesList.get(position));
button.setTag("grey");
button.setImageResource(R.drawable.heart_grey);
Toast.makeText(MainActivity.this,
MainActivity.this.getResources().getString(R.string.remove_favr),
Toast.LENGTH_SHORT).show();
}
return true;
}
});
// changing action bar color
getSupportActionBar().setBackgroundDrawable(
new ColorDrawable(Color.parseColor("#1b1b1b")));
// Creating volley request obj
JsonArrayRequest airlinesReq = new JsonArrayRequest(url,
new Response.Listener<JSONArray>() {
@Override
public void onResponse(JSONArray response) {
Log.d(TAG, response.toString());
hidePDialog();
// Parsing json
for (int i = 0; i < response.length(); i++) {
try {
JSONObject obj = response.getJSONObject(i);
Airlines airlines = new Airlines();
airlines.setName(obj.getString("name"));
airlines.setLogoURL(obj.getString("logoURL"));
airlines.setPhone(obj.getString("phone"));
airlines.setCode(obj.getInt("code"));
airlines.setSite(obj.getString("site"));
// adding airlines to array
airlinesList.add(airlines);
} catch (JSONException e) {
e.printStackTrace();
}
}
// notifying list adapterAirlines about data changes
// so that it renders the list view with updated data
adapterAirlines.notifyDataSetChanged();
}
}, new Response.ErrorListener() {
@Override
public void onErrorResponse(VolleyError error) {
VolleyLog.d(TAG, "Error: " + error.getMessage());
hidePDialog();
}
});
// Adding request to request queue
AppController.getInstance().addToRequestQueue(airlinesReq);
FragmentManager fragmentManager = getSupportFragmentManager();
/*
* This is called when orientation is changed.
*/
if (savedInstanceState != null) {
if (savedInstanceState.containsKey("content")) {
String content = savedInstanceState.getString("content");
if (content.equals(FavoriteFragment.ARG_ITEM_ID)) {
if (fragmentManager.findFragmentByTag(FavoriteFragment.ARG_ITEM_ID) != null) {
setFragmentTitle(R.string.favorites);
contentFragment = fragmentManager
.findFragmentByTag(FavoriteFragment.ARG_ITEM_ID);
}
}
}
if (fragmentManager.findFragmentByTag(AirlinesFragment.ARG_ITEM_ID) != null) {
airlinesFragment = (AirlinesFragment) fragmentManager
.findFragmentByTag(AirlinesFragment.ARG_ITEM_ID);
contentFragment = airlinesFragment;
}
} else {
airlinesFragment = new AirlinesFragment();
switchContent(airlinesFragment, AirlinesFragment.ARG_ITEM_ID);
}
/*
From this place DrawerLayout starts
*/
mTitle = mDrawerTitle = getTitle();
// load slide menu items
navMenuTitles = getResources().getStringArray(R.array.nav_drawer_items);
// nav drawer icons from resources
navMenuIcons = getResources()
.obtainTypedArray(R.array.nav_drawer_icons);
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.list_slidermenu);
navDrawerItems = new ArrayList<NavDrawerItem>();
// adding nav drawer items to array
// Home
navDrawerItems.add(new NavDrawerItem(navMenuTitles[0], navMenuIcons.getResourceId(0, -1)));
// Favorites
navDrawerItems.add(new NavDrawerItem(navMenuTitles[1], navMenuIcons.getResourceId(1, -1)));
// Recycle the typed array
navMenuIcons.recycle();
// setting the nav drawer list adapterDrawer
adapterDrawer = new NavDrawerListAdapter(getApplicationContext(),
navDrawerItems);
mDrawerList.setAdapter(adapterDrawer);
// enabling action bar app icon and behaving it as toggle button
getSupportActionBar().setDisplayHomeAsUpEnabled(true);
getSupportActionBar().setHomeButtonEnabled(true);
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
R.drawable.ic_drawer, //nav menu toggle icon
R.string.app_name, // nav drawer open - description for accessibility
R.string.app_name // nav drawer close - description for accessibility
){
public void onDrawerClosed(View view) {
getSupportActionBar().setTitle(mTitle);
// calling onPrepareOptionsMenu() to show action bar icons
invalidateOptionsMenu();
}
public void onDrawerOpened(View drawerView) {
getSupportActionBar().setTitle(mDrawerTitle);
// calling onPrepareOptionsMenu() to hide action bar icons
invalidateOptionsMenu();
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
if (savedInstanceState == null) {
// on first time display view for first nav item
displayView(0);
}
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// toggle nav drawer on selecting action bar app icon/title
// if (mDrawerToggle.onOptionsItemSelected(item)) {
// return true;
// }
// Handle action bar actions click
// switch (item.getItemId()) {
// case R.id.action_settings:
// return true;
// default:
// return super.onOptionsItemSelected(item);
// }
//
switch (item.getItemId()) {
case R.id.action_settings:
setFragmentTitle(R.string.favorites);
favoriteFragment = new FavoriteFragment();
switchContent(favoriteFragment, FavoriteFragment.ARG_ITEM_ID);
return true;
}
return super.onOptionsItemSelected(item);
}
/***
* Called when invalidateOptionsMenu() is triggered
*/
@Override
public boolean onPrepareOptionsMenu(Menu menu) {
// if nav drawer is opened, hide the action items
boolean drawerOpen = mDrawerLayout.isDrawerOpen(mDrawerList);
menu.findItem(R.id.action_settings).setVisible(!drawerOpen);
return super.onPrepareOptionsMenu(menu);
}
/**
* Diplaying fragment view for selected nav drawer list item
* */
private void displayView(int position) {
// update the main content by replacing fragments
Fragment fragment = null;
switch (position) {
case 0:
fragment = new HomeFragment();
break;
case 1:
fragment = new FavoriteFragment();
break;
default:
break;
}
if (fragment != null) {
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.frame_container, fragment).commit();
// update selected item and title, then close the drawer
mDrawerList.setItemChecked(position, true);
mDrawerList.setSelection(position);
setTitle(navMenuTitles[position]);
mDrawerLayout.closeDrawer(mDrawerList);
} else {
// error in creating fragment
Log.e("MainActivity", "Error in creating fragment");
}
}
@Override
public void setTitle(CharSequence title) {
mTitle = title;
getSupportActionBar().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);
}
@Override
public void onDestroy () {
super.onDestroy();
hidePDialog();
}
private void hidePDialog() {
if (pDialog != null) {
pDialog.dismiss();
pDialog = null;
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
@Override
protected void onSaveInstanceState(Bundle outState) {
if (contentFragment instanceof FavoriteFragment) {
outState.putString("content", FavoriteFragment.ARG_ITEM_ID);
} else {
outState.putString("content", AirlinesFragment.ARG_ITEM_ID);
}
super.onSaveInstanceState(outState);
}
public void switchContent(Fragment fragment, String tag) {
FragmentManager fragmentManager = getSupportFragmentManager();
while (fragmentManager.popBackStackImmediate()) ;
if (fragment != null) {
FragmentTransaction transaction = fragmentManager
.beginTransaction();
transaction.replace(R.id.content_frame, fragment, tag);
//Only FavoriteFragment is added to the back stack.
if (!(fragment instanceof AirlinesFragment)) {
transaction.addToBackStack(tag);
}
transaction.commit();
contentFragment = fragment;
}
}
protected void setFragmentTitle(int resourseId) {
setTitle(resourseId);
getSupportActionBar().setTitle(resourseId);
}
/*
* We call super.onBackPressed(); when the stack entry count is > 0. if it
* is instanceof ProductListFragment or if the stack entry count is == 0, then
* we finish the activity.
* In other words, from AirlinesFragment on back press it quits the app.
*/
@Override
public void onBackPressed() {
FragmentManager fm = getSupportFragmentManager();
if (fm.getBackStackEntryCount() > 0) {
super.onBackPressed();
} else if (contentFragment instanceof AirlinesFragment
|| fm.getBackStackEntryCount() == 0) {
finish();
}
}
@Override
public void onResume() {
super.onResume();
}
}
最喜欢的片段：
import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
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.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.AdapterView.OnItemLongClickListener;
import android.widget.ImageView;
import android.widget.ListView;
import android.widget.Toast;
import com.boom.kayakapp.R;
import com.boom.kayakapp.adapters.AirlinesAdapter;
import com.boom.kayakapp.model.Airlines;
import com.boom.kayakapp.util.SharedPreference;
import java.util.List;
public class FavoriteFragment extends Fragment {
public static final String ARG_ITEM_ID = "favorite_list";
ListView favoriteList;
SharedPreference sharedPreference;
List<Airlines> favorites;
Activity activity;
AirlinesAdapter airlinesAdapter;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
activity = getActivity();
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View view = inflater.inflate(R.layout.activity_list, container,
false);
// Get favorite items from SharedPreferences.
sharedPreference = new SharedPreference();
favorites = sharedPreference.getFavorites(activity);
if (favorites == null) {
showAlert(getResources().getString(R.string.no_favorites_items),
getResources().getString(R.string.no_favorites_msg));
} else {
if (favorites.size() == 0) {
showAlert(
getResources().getString(R.string.no_favorites_items),
getResources().getString(R.string.no_favorites_msg));
}
favoriteList = (ListView) view.findViewById(R.id.list);
if (favorites != null) {
airlinesAdapter = new AirlinesAdapter(activity, favorites);
favoriteList.setAdapter(airlinesAdapter);
favoriteList.setOnItemClickListener(new OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View arg1,
int position, long arg3) {
}
});
favoriteList
.setOnItemLongClickListener(new OnItemLongClickListener() {
@Override
public boolean onItemLongClick(
AdapterView<?> parent, View view,
int position, long id) {
ImageView button = (ImageView) view
.findViewById(R.id.favorite_button);
String tag = button.getTag().toString();
if (tag.equalsIgnoreCase("grey")) {
sharedPreference.addFavorite(activity,
favorites.get(position));
Toast.makeText(
activity,
activity.getResources().getString(
R.string.add_favr),
Toast.LENGTH_SHORT).show();
button.setTag("red");
button.setImageResource(R.drawable.heart_red);
} else {
sharedPreference.removeFavorite(activity,
favorites.get(position));
button.setTag("grey");
button.setImageResource(R.drawable.heart_grey);
airlinesAdapter.remove(favorites
.get(position));
Toast.makeText(
activity,
activity.getResources().getString(
R.string.remove_favr),
Toast.LENGTH_SHORT).show();
}
return true;
}
});
}
}
return view;
}
public void showAlert(String title, String message) {
if (activity != null && !activity.isFinishing()) {
AlertDialog alertDialog = new AlertDialog.Builder(activity)
.create();
alertDialog.setTitle(title);
alertDialog.setMessage(message);
alertDialog.setCancelable(false);
// setting OK Button
alertDialog.setButton(AlertDialog.BUTTON_POSITIVE, "OK",
new DialogInterface.OnClickListener() {
public void onClick(DialogInterface dialog, int which) {
dialog.dismiss();
// activity.finish();
getFragmentManager().popBackStackImmediate();
}
});
alertDialog.show();
}
}
@Override
public void onResume() {
getActivity().setTitle(R.string.favorites);
super.onResume();
}
}