我从头开始重写我的应用程序，因为我希望它更现代和直观。为此，我使用带有片段的NavigationDrawer布局。
现在我希望用户点击其中一个NavigationDrawer选项启动另一个活动（不是片段），这是一个壁纸选择器。
我的代码有效，但是当用户这样做时，MainActivity崩溃了。为什么呢？
以下是MainActivity：
public class MainActivity extends Activity {
private DrawerLayout mDrawerLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
private CharSequence mDrawerTitle;
private CharSequence mTitle;
CustomDrawerAdapter adapter;
List<DrawerItem> dataList;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
// Initializing
dataList = new ArrayList<DrawerItem>();
mTitle = mDrawerTitle = getTitle();
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerList = (ListView) findViewById(R.id.left_drawer);
mDrawerLayout.setDrawerShadow(R.drawable.drawer_shadow,
GravityCompat.START);
// Add Drawer Item to dataList
dataList.add(new DrawerItem("Launchers", R.drawable.ic_action_email));
dataList.add(new DrawerItem("Extras", R.drawable.ic_action_good));
dataList.add(new DrawerItem("Support", R.drawable.ic_action_gamepad));
dataList.add(new DrawerItem("Contact", R.drawable.ic_action_labels));
dataList.add(new DrawerItem("Wallpapers", R.drawable.ic_action_search));
dataList.add(new DrawerItem("Import & Export",
R.drawable.ic_action_import_export));
dataList.add(new DrawerItem("About", R.drawable.ic_action_about));
dataList.add(new DrawerItem("Settings", R.drawable.ic_action_settings));
dataList.add(new DrawerItem("Help", R.drawable.ic_action_help));
adapter = new CustomDrawerAdapter(this, R.layout.custom_drawer_item,
dataList);
mDrawerList.setAdapter(adapter);
mDrawerList.setOnItemClickListener(new DrawerItemClickListener());
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
R.drawable.ic_drawer, R.string.drawer_open,
R.string.drawer_close) {
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) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
public void goToWallpaper (View view) {
Intent intent = new Intent(this, Wallpaper.class);
startActivity(intent);
}
public void SelectItem(int position) {
Fragment fragment = null;
Bundle args = new Bundle();
switch (position) {
case 0:
fragment = new FragmentOne();
break;
case 1:
fragment = new FragmentTwo();
break;
case 2:
fragment = new FragmentThree();
break;
case 3:
fragment = new FragmentFour();
break;
case 4:
startActivity(new Intent(this, Wallpaper.class));
break;
default:
break;
}
fragment.setArguments(args);
FragmentManager frgManager = getFragmentManager();
frgManager.beginTransaction().replace(R.id.content_frame, fragment)
.commit();
mDrawerList.setItemChecked(position, true);
setTitle(dataList.get(position).getItemName());
mDrawerLayout.closeDrawer(mDrawerList);
}
@Override
public void setTitle(CharSequence title) {
mTitle = title;
getActionBar().setTitle(mTitle);
}
@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 toggles
mDrawerToggle.onConfigurationChanged(newConfig);
}
@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;
}
return false;
}
private class DrawerItemClickListener implements
ListView.OnItemClickListener {
@Override
public void onItemClick(AdapterView<?> parent, View view, int position,
long id) {
SelectItem(position);
}
}
}
这是壁纸活动：
public class Wallpaper extends SherlockActivity implements AdapterView.OnItemSelectedListener,
OnClickListener {
private Gallery mGallery;
private ImageView mImageView;
private boolean mIsWallpaperSet;
private Bitmap mBitmap;
private ArrayList<Integer> mThumbs;
private ArrayList<Integer> mImages;
private WallpaperLoader mLoader;
@Override
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
requestWindowFeature(Window.FEATURE_NO_TITLE);
findWallpapers();
setContentView(R.layout.wallpaper_chooser);
mGallery = (Gallery) findViewById(R.id.gallery);
mGallery.setAdapter(new ImageAdapter(this));
mGallery.setOnItemSelectedListener(this);
mGallery.setCallbackDuringFling(false);
findViewById(R.id.set).setOnClickListener(this);
mImageView = (ImageView) findViewById(R.id.wallpaper);
}
private void findWallpapers() {
mThumbs = new ArrayList<Integer>(24);
mImages = new ArrayList<Integer>(24);
final Resources resources = getResources();
final String packageName = getApplication().getPackageName();
addWallpapers(resources, packageName, R.array.wallpapers);
addWallpapers(resources, packageName, R.array.extra_wallpapers);
}
private void addWallpapers(Resources resources, String packageName, int list) {
final String[] extras = resources.getStringArray(list);
for (String extra : extras) {
int res = resources.getIdentifier(extra, "drawable", packageName);
if (res != 0) {
final int thumbRes = resources.getIdentifier(extra + "_small",
"drawable", packageName);
if (thumbRes != 0) {
mThumbs.add(thumbRes);
mImages.add(res);
}
}
}
}
@Override
protected void onResume() {
super.onResume();
mIsWallpaperSet = false;
}
@Override
protected void onDestroy() {
super.onDestroy();
if (mLoader != null && mLoader.getStatus() != WallpaperLoader.Status.FINISHED) {
mLoader.cancel(true);
mLoader = null;
}
}
@Override
public void onItemSelected(AdapterView<?> parent, View v, int position, long id) {
if (mLoader != null && mLoader.getStatus() != WallpaperLoader.Status.FINISHED) {
mLoader.cancel();
}
mLoader = (WallpaperLoader) new WallpaperLoader().execute(position);
}
private void selectWallpaper(int position) {
if (mIsWallpaperSet) {
return;
}
mIsWallpaperSet = true;
try {
InputStream stream = getResources().openRawResource(mImages.get(position));
setWallpaper(stream);
setResult(RESULT_OK);
finish();
} catch (IOException e) {
Log.e("Template", "Failed to set wallpaper: " + e);
}
}
@Override
public void onNothingSelected(AdapterView<?> parent) {
}
private class ImageAdapter extends BaseAdapter {
private LayoutInflater mLayoutInflater;
ImageAdapter(Wallpaper context) {
mLayoutInflater = context.getLayoutInflater();
}
@Override
public int getCount() {
return mThumbs.size();
}
@Override
public Object getItem(int position) {
return position;
}
@Override
public long getItemId(int position) {
return position;
}
@Override
public View getView(int position, View convertView, ViewGroup parent) {
ImageView image;
if (convertView == null) {
image = (ImageView) mLayoutInflater.inflate(R.layout.wallpaper_item, parent, false);
} else {
image = (ImageView) convertView;
}
int thumbRes = mThumbs.get(position);
image.setImageResource(thumbRes);
Drawable thumbDrawable = image.getDrawable();
if (thumbDrawable != null) {
thumbDrawable.setDither(true);
} else {
Log.e("Template", String.format(
"Error decoding thumbnail resId=%d for wallpaper #%d",
thumbRes, position));
}
return image;
}
}
@Override
public void onClick(View v) {
selectWallpaper(mGallery.getSelectedItemPosition());
}
class WallpaperLoader extends AsyncTask<Integer, Void, Bitmap> {
BitmapFactory.Options mOptions;
WallpaperLoader() {
mOptions = new BitmapFactory.Options();
mOptions.inDither = false;
mOptions.inPreferredConfig = Bitmap.Config.ARGB_8888;
}
@Override
protected Bitmap doInBackground(Integer... params) {
if (isCancelled()) return null;
try {
return BitmapFactory.decodeResource(getResources(),
mImages.get(params[0]), mOptions);
} catch (OutOfMemoryError e) {
return null;
}
}
@Override
protected void onPostExecute(Bitmap b) {
if (b == null) return;
if (!isCancelled() && !mOptions.mCancel) {
if (mBitmap != null) {
mBitmap.recycle();
}
final ImageView view = mImageView;
view.setImageBitmap(b);
mBitmap = b;
final Drawable drawable = view.getDrawable();
drawable.setFilterBitmap(true);
drawable.setDither(true);
view.postInvalidate();
mLoader = null;
} else {
b.recycle();
}
}
void cancel() {
mOptions.requestCancelDecode();
super.cancel(true);
}
}
}
如果它有帮助，这就是logcat：
04-19 14:59:41.735: W/dalvikvm(11025): threadid=1: thread exiting with uncaught exception (group=0x41961da0)
04-19 14:59:41.735: E/AndroidRuntime(11025): FATAL EXCEPTION: main
04-19 14:59:41.735: E/AndroidRuntime(11025): Process: com.tutecentral.navigationdrawer, PID: 11025
04-19 14:59:41.735: E/AndroidRuntime(11025): java.lang.NullPointerException
04-19 14:59:41.735: E/AndroidRuntime(11025): at com.tutecentral.navigationdrawer.MainActivity.SelectItem(MainActivity.java:143)
04-19 14:59:41.735: E/AndroidRuntime(11025): at com.tutecentral.navigationdrawer.MainActivity$DrawerItemClickListener.onItemClick(MainActivity.java:190)
04-19 14:59:41.735: E/AndroidRuntime(11025): at android.widget.AdapterView.performItemClick(AdapterView.java:308)
04-19 14:59:41.735: E/AndroidRuntime(11025): at android.widget.AbsListView.performItemClick(AbsListView.java:1476)
04-19 14:59:41.735: E/AndroidRuntime(11025): at android.widget.AbsListView$PerformClick.run(AbsListView.java:3497)
04-19 14:59:41.735: E/AndroidRuntime(11025): at android.widget.AbsListView$3.run(AbsListView.java:4814)
04-19 14:59:41.735: E/AndroidRuntime(11025): at android.os.Handler.handleCallback(Handler.java:733)
04-19 14:59:41.735: E/AndroidRuntime(11025): at android.os.Handler.dispatchMessage(Handler.java:95)
04-19 14:59:41.735: E/AndroidRuntime(11025): at android.os.Looper.loop(Looper.java:157)
04-19 14:59:41.735: E/AndroidRuntime(11025): at android.app.ActivityThread.main(ActivityThread.java:5293)
04-19 14:59:41.735: E/AndroidRuntime(11025): at java.lang.reflect.Method.invokeNative(Native Method)
04-19 14:59:41.735: E/AndroidRuntime(11025): at java.lang.reflect.Method.invoke(Method.java:515)
04-19 14:59:41.735: E/AndroidRuntime(11025): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1265)
04-19 14:59:41.735: E/AndroidRuntime(11025): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1081)
04-19 14:59:41.735: E/AndroidRuntime(11025): at dalvik.system.NativeStart.main(Native Method)
万分感谢！
答案 0 :(得分：0)
正如logcat指出问题出在SelectItem方法中。
在顶部，您将片段定义为null：
Fragment fragment = null;
但是在切换之后你尝试这样做：
fragment.setArguments(args); // If the fragment is null, an Exception will occur
我认为你背后的推理是你打电话
case 4:
startActivity(new Intent(this, Wallpaper.class));
break;
在这里，这将结束Activity并且它永远不会到达交换机下方的任何内容，但这是错误的。即使您开始使用新的Activity，旧的startActivity即使在调用Activity之后，旧的if(fragment != null) {
fragment.setArguments(args);
FragmentManager frgManager = getFragmentManager();
frgManager.beginTransaction().replace(R.id.content_frame, fragment)
.commit();
}
仍然会完成该方法并继续其正常的生命周期。所以你需要做的是：
{{1}}