我按照有效的导航示例。构建一个新的应用程序。基本上我想要的是每个短信应该出现在我的应用程序的新屏幕（片段）上，并且可以滚动，就像Gmail App中的Gmail邮件一样
这是相同的代码
package com.example.android.effectivenavigation;
import java.sql.Date;
import java.text.SimpleDateFormat;
import java.util.Locale;
import android.app.ActionBar;
import android.content.Intent;
import android.database.Cursor;
import android.net.Uri;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentStatePagerAdapter;
import android.support.v4.app.LoaderManager;
import android.support.v4.app.NavUtils;
import android.support.v4.app.TaskStackBuilder;
import android.support.v4.content.CursorLoader;
import android.support.v4.content.Loader;
import android.support.v4.view.ViewPager;
import android.support.v4.widget.SimpleCursorAdapter;
import android.view.LayoutInflater;
import android.view.MenuItem;
import android.view.View;
import android.view.ViewGroup;
import android.widget.TextView;
public class CollectionDemoActivity extends FragmentActivity implements LoaderManager.LoaderCallbacks<Cursor> {
/**
* The {@link android.support.v4.view.PagerAdapter} that will provide fragments representing each object in a
* collection. We use a {@link android.support.v4.app.FragmentStatePagerAdapter} derivative, which will destroy and
* re-create fragments as needed, saving and restoring their state in the process. This is important to conserve
* memory and is a best practice when allowing navigation between objects in a potentially large collection.
*/
DemoCollectionPagerAdapter mDemoCollectionPagerAdapter;
// This is the Adapter being used to display the list's data.
SimpleCursorAdapter mAdapter;
/**
* The {@link android.support.v4.view.ViewPager} that will display the object collection.
*/
ViewPager mViewPager;
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_collection_demo);
//-----------------------THIS BLOCK WORK JUST FINE--------------------------
Cursor cursor = getContentResolver().query(Uri.parse("content://sms/inbox"), null, null, null, null);
cursor.moveToFirst();
do {
String msgData = "a";
for (int idx = 0; idx < cursor.getColumnCount(); idx++) {
msgData += " " + cursor.getColumnName(idx) + ":" + cursor.getString(idx);
}
Date date = new Date(Long.parseLong(cursor.getString(5)));
SimpleDateFormat sdf = new SimpleDateFormat("E yyyy.MM.dd 'at' hh:mm:ss a zzz",Locale.ENGLISH);
System.out.println("Cursor123"+msgData + "\r Dateeeee" + sdf.format(date));
} while (cursor.moveToNext());
//-----------------------------END BLOCK ----------------------------------
// Create an adapter that when requested, will return a fragment representing an object in
// the collection.
//
// ViewPager and its adapters use support library fragments, so we must use
// getSupportFragmentManager.
mDemoCollectionPagerAdapter = new DemoCollectionPagerAdapter(getSupportFragmentManager());
// Set up action bar.
final ActionBar actionBar = getActionBar();
// Specify that the Home button should show an "Up" caret, indicating that touching the
// button will take the user one step up in the application's hierarchy.
actionBar.setDisplayHomeAsUpEnabled(true);
// Set up the ViewPager, attaching the adapter.
mViewPager = (ViewPager) findViewById(R.id.pager);
getSupportLoaderManager().initLoader(0, null, this);
mAdapter = new SimpleCursorAdapter(this, R.layout.activity_collection_demo, null, null, null, 0);
Cursor cursor1 = mAdapter.getCursor();
mDemoCollectionPagerAdapter.setCount(cursor1.getCount());
mViewPager.setAdapter(mDemoCollectionPagerAdapter);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
Intent upIntent = new Intent(this, MainActivity.class);
if (NavUtils.shouldUpRecreateTask(this, upIntent)) {
// This activity is not part of the application's task, so create a new task
// with a synthesized back stack.
TaskStackBuilder.from(this)
// If there are ancestor activities, they should be added here.
.addNextIntent(upIntent).startActivities();
finish();
} else {
// This activity is part of the application's task, so simply
// navigate up to the hierarchical parent activity.
NavUtils.navigateUpTo(this, upIntent);
}
return true;
}
return super.onOptionsItemSelected(item);
}
/**
* A {@link android.support.v4.app.FragmentStatePagerAdapter} that returns a fragment representing an object in the
* collection.
*/
public static class DemoCollectionPagerAdapter extends FragmentStatePagerAdapter {
public DemoCollectionPagerAdapter(FragmentManager fm) {
super(fm);
}
private int count;
@Override
public Fragment getItem(int i) {
Fragment fragment = new DemoObjectFragment();
Bundle args = new Bundle();
args.putInt(DemoObjectFragment.ARG_OBJECT, i + 1);
fragment.setArguments(args);
return fragment;
}
@Override
public int getCount() {
// temporarily setting count to 5
return 5;
}
public void setCount( int iCount) {
this.count=iCount;
}
@Override
public CharSequence getPageTitle(int position) {
return "OBJECT " + (position + 1);
}
}
/**
* A dummy fragment representing a section of the app, but that simply displays dummy text.
*/
public static class DemoObjectFragment extends Fragment {
public static final String ARG_OBJECT = "object";
Cursor cursor;
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_collection_object, container, false);
Bundle args = getArguments();
((TextView) rootView.findViewById(android.R.id.text1)).setText(Integer.toString(args.getInt(ARG_OBJECT)));
// cursor.move(args.getInt(ARG_OBJECT));
TextView tv1 = (TextView) getActivity().findViewById(R.id.editText1);
tv1.setText("Test");
return rootView;
}
}
@Override
public Loader<Cursor> onCreateLoader(int id, Bundle args) {
Uri baseUri = Uri.parse("content://sms/inbox");
return new CursorLoader(this, baseUri, null, null, null, null);
}
@Override
public void onLoadFinished(Loader<Cursor> loader, Cursor data) {
mAdapter.swapCursor(data);
}
@Override
public void onLoaderReset(Loader<Cursor> loader) {
mAdapter.swapCursor(null);
}
}
这是异常的堆栈跟踪：
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.android.effectivenavigation/com.example.android.effectivenavigation.CollectionDemoActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1956)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
at android.app.ActivityThread.access$600(ActivityThread.java:123)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4424)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:511)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.example.android.effectivenavigation.CollectionDemoActivity.onCreate(CollectionDemoActivity.java:108)
at android.app.Activity.performCreate(Activity.java:4465)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1920)
... 11 more
线108对应于
“mDemoCollectionPagerAdapter.setCount（cursor1.getCount（））;”
你的SimpleCursorAdapter开始（并且直到Loader做它的工作）当时有一个空的Cursor所以：
mDemoCollectionPagerAdapter.setCount(cursor1.getCount());
将抛出该异常，因为cursor1是null。相反，你应该在ViewPager回调中更新count的onLoadFinished变量，因为在那一刻Cursor应该是有效的，你可以获得其中的行数。