当我在我的应用程序中的片段中插入listview时，在我用项目填充它后它不会显示。实际上，应用程序由于NullPointerException而崩溃。有谁能够帮我？这是我展示片段的详细活动。
package com.example.sample;
import android.content.Intent;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentTransaction;
import android.support.v4.app.NavUtils;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import com.actionbarsherlock.app.ActionBar;
import com.actionbarsherlock.app.ActionBar.Tab;
import com.actionbarsherlock.app.SherlockFragmentActivity;
import com.actionbarsherlock.view.MenuItem;
/**
* An activity representing a single Course detail screen. This activity is only
* used on handset devices. On tablet-size devices, item details are presented
* side-by-side with a list of items in a {@link CourseListActivity}.
* <p>
* This activity is mostly just a 'shell' activity containing nothing more than
* a {@link CourseDetailFragment}.
*/
public class CourseDetailActivity extends SherlockFragmentActivity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_course_detail);
// Show the Up button in the action bar.
ActionBar actionBar = getSupportActionBar();
actionBar.setDisplayHomeAsUpEnabled(true);
actionBar.setNavigationMode(ActionBar.NAVIGATION_MODE_TABS);
// initiating both tabs and set text to it.
ActionBar.Tab assignTab = actionBar.newTab().setText("Assignments");
ActionBar.Tab schedTab = actionBar.newTab().setText("Schedule");
ActionBar.Tab contactTab = actionBar.newTab().setText("Contact");
// Create three fragments to display content
Fragment assignFragment = new Assignments();
Fragment schedFragment = new Schedule();
Fragment contactFragment = new Contact();
assignTab.setTabListener(new MyTabsListener(assignFragment));
schedTab.setTabListener(new MyTabsListener(schedFragment));
contactTab.setTabListener(new MyTabsListener(contactFragment));
actionBar.addTab(assignTab);
actionBar.addTab(schedTab);
actionBar.addTab(contactTab);
ListView listView = (ListView) findViewById(R.id.assignlist);
String[] values = new String[] { "Android", "iPhone", "WindowsMobile",
"Blackberry", "WebOS", "Ubuntu", "Windows7", "Max OS X",
"Linux", "OS/2" };
// First paramenter - Context
// Second parameter - Layout for the row
// Third parameter - ID of the TextView to which the data is written
// Forth - the Array of data
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, android.R.id.text1, values);
// Assign adapter to ListView
listView.setAdapter(adapter);
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case android.R.id.home:
// This ID represents the Home or Up button. In the case of this
// activity, the Up button is shown. Use NavUtils to allow users
// to navigate up one level in the application structure. For
// more details, see the Navigation pattern on Android Design:
//
// http://developer.android.com/design/patterns/navigation.html#up-vs-back
//
NavUtils.navigateUpTo(this, new Intent(this,
CourseListActivity.class));
return true;
}
return super.onOptionsItemSelected(item);
}
class MyTabsListener implements ActionBar.TabListener {
public Fragment fragment;
public Fragment fragment2;
public MyTabsListener(Fragment fragment) {
this.fragment = fragment;
}
@Override
public void onTabReselected(Tab tab, FragmentTransaction ft) {
}
@Override
public void onTabSelected(Tab tab, FragmentTransaction ft) {
ft.replace(R.id.main_across, fragment);
}
@Override
public void onTabUnselected(Tab tab, FragmentTransaction ft) {
ft.remove(fragment);
}
}
}
我目前正在努力工作的片段称为Assignments片段。正如您在CourseDetailActvity中所看到的，我在listview中填充了smaple项目以查看listview是否显示。片段被正确充气，但当我尝试将项目添加到列表视图时，应用程序崩溃了！
这是logcat。
11-17 11:54:28.037: E/AndroidRuntime(282): FATAL EXCEPTION: main
11-17 11:54:28.037: E/AndroidRuntime(282): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.sample/com.example.sample.CourseDetailActivity}: java.lang.NullPointerException
11-17 11:54:28.037: E/AndroidRuntime(282): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
11-17 11:54:28.037: E/AndroidRuntime(282): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
11-17 11:54:28.037: E/AndroidRuntime(282): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
11-17 11:54:28.037: E/AndroidRuntime(282): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
11-17 11:54:28.037: E/AndroidRuntime(282): at android.os.Handler.dispatchMessage(Handler.java:99)
11-17 11:54:28.037: E/AndroidRuntime(282): at android.os.Looper.loop(Looper.java:123)
11-17 11:54:28.037: E/AndroidRuntime(282): at android.app.ActivityThread.main(ActivityThread.java:4627)
11-17 11:54:28.037: E/AndroidRuntime(282): at java.lang.reflect.Method.invokeNative(Native Method)
11-17 11:54:28.037: E/AndroidRuntime(282): at java.lang.reflect.Method.invoke(Method.java:521)
11-17 11:54:28.037: E/AndroidRuntime(282): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
11-17 11:54:28.037: E/AndroidRuntime(282): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
11-17 11:54:28.037: E/AndroidRuntime(282): at dalvik.system.NativeStart.main(Native Method)
11-17 11:54:28.037: E/AndroidRuntime(282): Caused by: java.lang.NullPointerException
11-17 11:54:28.037: E/AndroidRuntime(282): at com.example.sample.CourseDetailActivity.onCreate(CourseDetailActivity.java:66)
11-17 11:54:28.037: E/AndroidRuntime(282): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
11-17 11:54:28.037: E/AndroidRuntime(282): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
11-17 11:54:28.037: E/AndroidRuntime(282): ... 11 more
答案 0 :(得分：0)
我相信你的崩溃就在这条线上：
listView.setAdapter(adapter);
adapter显然不为空（崩溃不在setAdapter()范围内），因此listView必须为空。
ListView listView = (ListView) findViewById(R.id.assignlist);
嗯，我们可以看到它在那里宣布。但是，如果找不到该对象，findViewById()可以返回null。您正在使用的布局（ListView）中似乎没有ID assignlist的对象（特别是没有activity_course_detail.xml）。