我不知道出了什么问题，每当我在模拟器上启动我的应用并将其切换到横屏模式时，应用就会崩溃。但是在竖屏模式下运行良好。请问我该怎么做才能解决这个问题。提前感谢！以下是我的代码...
MainActivity.class
import android.app.FragmentTransaction;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import com.actgeek.android.myapplication.R;
public class MainActivity extends AppCompatActivity{
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
MAFragment mfrag = new MAFragment();
FragmentTransaction FT = getFragmentManager().beginTransaction();
FT.replace(R.id.fragment, mfrag);
FT.commit();
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
这个片段在activity_main布局中显示。
MAFragment.class
public class MAFragment extends ListFragment {
public MAFragment() {
}
@Override
public void onActivityCreated(Bundle savedInstanceState){
super.onActivityCreated(savedInstanceState);
String topics[] = Mylists.TOPICS;
MyArrayAdapter adapter = new MyArrayAdapter(getActivity(),
topics);
setListAdapter(adapter);
getListView().setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int
position, long id) {
Intent intent = new Intent(getActivity(), SubTopicsActivity.class);
intent.putExtra("index", position);
startActivity(intent);
}
});
}
}
主活动布局
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:app="http://schemas.android.com/apk/res-auto"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:layout="@layout/fragment_main"
tools:context="com.actgeek.android.studypack.MainActivity">
<fragment android:id="@+id/fragment"
android:name="com.actgeek.android.studypack.MAFragment"
android:layout_width="match_parent"
android:layout_height="match_parent"
app:layout_behavior="@string/appbar_scrolling_view_behavior"/>
</LinearLayout>
每当应用程序崩溃时，我都会遇到以下错误信息。
12-19 11:08:18.383 28644-28644/com.actgeek.android.myapplication E/AndroidRuntime: FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.actgeek.android.myapplication/com.actgeek.android.studypack.MainActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2412)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3919)
at android.app.ActivityThread.access$700(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1370)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5388)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:94)
at android.support.v7.internal.widget.ToolbarWidgetWrapper.<init>(ToolbarWidgetWrapper.java:87)
at android.support.v7.internal.app.ToolbarActionBar.<init>(ToolbarActionBar.java:77)
at android.support.v7.app.AppCompatDelegateImplV7.setSupportActionBar(AppCompatDelegateImplV7.java:198)
at android.support.v7.app.AppCompatActivity.setSupportActionBar(AppCompatActivity.java:96)
at com.actgeek.android.studypack.MainActivity.onCreate(MainActivity.java:28)
at android.app.Activity.performCreate(Activity.java:5141)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1084)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2307)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2412)
at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3919)
at android.app.ActivityThread.access$700(ActivityThread.java:162)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1370)
at android.os.Handler.dispatchMessage(Handler.java:107)
at android.os.Looper.loop(Looper.java:194)
at android.app.ActivityThread.main(ActivityThread.java:5388)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:833)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:600)
at dalvik.system.NativeStart.main(Native Method)
activity_main中没有它。如果你的意思是你有不同的纵向和横向布局，那么工具栏需要在两个布局中都存在。 - Mike M.content_main在您发布的布局中包含在哪里，或者在您展示的代码中被加载了吗？ - Mike M.