Java Nullpointer异常-碎片活动
我在fragmentactivity中收到一个nullpointer异常错误 以下是日志目录:Java Nullpointer异常-碎片活动,java,android,android-layout,android-activity,android-fragments,Java,Android,Android Layout,Android Activity,Android Fragments,我在fragmentactivity中收到一个nullpointer异常错误 以下是日志目录: 11-04 06:29:51.550: E/AndroidRuntime(19286): FATAL EXCEPTION: main 11-04 06:29:51.550: E/AndroidRuntime(19286): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dooba.beta/com.doob
11-04 06:29:51.550: E/AndroidRuntime(19286): FATAL EXCEPTION: main
11-04 06:29:51.550: E/AndroidRuntime(19286): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.dooba.beta/com.dooba.beta.MainActivity}: java.lang.NullPointerException
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.app.ActivityThread.access$600(ActivityThread.java:130)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.os.Handler.dispatchMessage(Handler.java:99)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.os.Looper.loop(Looper.java:137)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.app.ActivityThread.main(ActivityThread.java:4745)
11-04 06:29:51.550: E/AndroidRuntime(19286): at java.lang.reflect.Method.invokeNative(Native Method)
11-04 06:29:51.550: E/AndroidRuntime(19286): at java.lang.reflect.Method.invoke(Method.java:511)
11-04 06:29:51.550: E/AndroidRuntime(19286): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
11-04 06:29:51.550: E/AndroidRuntime(19286): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
11-04 06:29:51.550: E/AndroidRuntime(19286): at dalvik.system.NativeStart.main(Native Method)
11-04 06:29:51.550: E/AndroidRuntime(19286): Caused by: java.lang.NullPointerException
11-04 06:29:51.550: E/AndroidRuntime(19286): at com.dooba.beta.MainActivity.onCreate(MainActivity.java:51)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.app.Activity.performCreate(Activity.java:5008)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
11-04 06:29:51.550: E/AndroidRuntime(19286): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
11-04 06:29:51.550: E/AndroidRuntime(19286): ... 11 more
我认为错误发生在以下几行中:
mDrawerList.setAdapter(new ArrayAdapter<String>(getActionBar()
.getThemedContext(), android.R.layout.simple_list_item_1,
mOptionMenu));
以下是整个活动代码:
import android.app.ActionBar;
import android.app.Activity;
import android.content.res.Configuration;
import android.os.Bundle;
import android.support.v4.app.ActionBarDrawerToggle;
import android.support.v4.app.ActivityCompat;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.widget.DrawerLayout;
import android.view.Menu;
import android.view.MenuItem;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.RelativeLayout;
import android.widget.Toast;
public class MainActivity extends FragmentActivity {
private String[] mOptionMenu;
private DrawerLayout mDrawerLayout;
private RelativeLayout mDrawerRelativeLayout;
private ListView mDrawerList;
private ActionBarDrawerToggle mDrawerToggle;
private CharSequence mTitleSection;
private CharSequence mTitleApp;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mOptionMenu = new String[] { "Opción 1", "Opción 2", "Opción 3" };
mDrawerLayout = (DrawerLayout) findViewById(R.id.drawer_layout);
mDrawerRelativeLayout = (RelativeLayout)
findViewById(R.id.left_drawer);
mDrawerList = (ListView) findViewById(R.id.list_view_drawer);
mDrawerList.setAdapter(new ArrayAdapter<String>(getActionBar()
.getThemedContext(), android.R.layout.simple_list_item_1,
mOptionMenu));
mDrawerList.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> parent, View view,
int position, long id) {
Fragment fragment = null;
switch (position) {
case 0:
fragment = new FirstFragment();
break;
case 1:
fragment = new SecondFragment();
break;
case 2:
fragment = new ThirdFragment();
break;
}
FragmentManager fragmentManager = getSupportFragmentManager();
fragmentManager.beginTransaction()
.replace(R.id.content_frame, fragment).commit();
mDrawerList.setItemChecked(position, true);
mTitleSection = mOptionMenu[position];
getActionBar().setTitle(mTitleSection);
mDrawerLayout.closeDrawer(mDrawerRelativeLayout);
}
});
mDrawerList.setItemChecked(0, true);
mTitleSection = getTitle();
mTitleApp = getTitle();
mDrawerToggle = new ActionBarDrawerToggle(this, mDrawerLayout,
R.drawable.ic_drawer, R.string.drawer_open,
R.string.drawer_close) {
public void onDrawerClosed(View view) {
getActionBar().setTitle(mTitleSection);
ActivityCompat.invalidateOptionsMenu(MainActivity.this);
}
public void onDrawerOpened(View drawerView) {
getActionBar().setTitle(mTitleSection);
ActivityCompat.invalidateOptionsMenu(MainActivity.this);
}
};
mDrawerLayout.setDrawerListener(mDrawerToggle);
getActionBar().setDisplayHomeAsUpEnabled(true);
getActionBar().setHomeButtonEnabled(true);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
getMenuInflater().inflate(R.menu.main_activity_actions, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if (mDrawerToggle.onOptionsItemSelected(item)) {
return true;
}
switch (item.getItemId()) {
case R.id.action_settings:
Toast.makeText(this, "Settings", Toast.LENGTH_SHORT).show();
;
break;
default:
return super.onOptionsItemSelected(item);
}
return true;
}
@Override
protected void onPostCreate(Bundle savedInstanceState) {
super.onPostCreate(savedInstanceState);
mDrawerToggle.syncState();
}
@Override
public void onConfigurationChanged(Configuration newConfig) {
super.onConfigurationChanged(newConfig);
mDrawerToggle.onConfigurationChanged(newConfig);
}
}
如果需要任何澄清,请告诉我。
提前谢谢。代替
getActionBar().getThemedContext()
使用此因为您要导入import android.support.v7.app.ActionBarActivity,我想您应该使用
getSupportActionBar()
而不是
getActionBar()
getActionBar和mDrawerList的值是什么?要想知道什么是null,最简单的方法是将错误行中的所有方法和变量分离到它们自己的变量中,然后在那里放置一个断点并进行步骤调试感谢您的响应。你所说的getActionBar的值到底是什么意思?正如@StackFlowed所说的,主要需要检查这两个值中的哪一个:mDrawerList,getActionBar给你一个空值看看Lukas的答案。getActionBar在您构建到的API级别中不受支持。所以它总是返回null。您需要提高API级别,或者在目标API级别内使用受支持的API调用。谢谢您的建议。应用它后,我在以下行收到以下nullpoint异常错误:getActionBar.SetDisplayHomeAsupanabledTrue;我不确定,但我认为这取决于你使用的主题。如果你的应用程序主题没有操作栏,你将返回null。如果你的主题有ActivoJ栏,那么让你的活动扩展ActionBarActivity:它是FragmentActivity的一个子类,所以你应该没有问题,而不是调用getActionBar,你必须调用getSupportActionBar,因为FragmentActivity和ActionBarActivity是支持库的一部分。我再说一遍,我不是100%确定,如果您找到了解决方案,请告诉我这是应用程序或活动@style/theme.AppCompat.Light>使用的主题,这是@style/Widget.AppCompat.actionbar使用的actionbar样式的主题。然后尝试使用ActionBarActivity和GetSupportActionBar的解决方案您是对的,改用ActionBarActivity和get SupportActionBar解决了这个问题。因为我想在5.0以下的早期版本的android上运行它,所以我决定使用getActionBar,这就是问题的根源。我想这是正确的答案。您尝试过getSupportActionBar吗?getSupportActionBar可从API v7(包括v21)获得getActionBar刚从v11(包括v21)开始在显示片段的活动中引用哪个ActionBar活动很重要。