问题
I am trying to start a new activity(Settings Activity) from onOptionsItemSelected, but i am getting fatal exception when i click on option two it starts settings activity for a while than it crashes.
if i start Settings Activity from any where else than it starts without any error.
SettingsActivity
import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
public class SettingsActivity extends Activity {
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_settings);
}
}
First activity(Room1.java):
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_room1);
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
MenuInflater inflator = getMenuInflater();
inflator.inflate(R.menu.room1, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
if(item.getItemId()==R.id.menu_option_two){
Settings();
Log.d("Option","2");
}
return super.onOptionsItemSelected(item);
}
private void Settings() {
Intent intent = new Intent(this, SettingsActivity.class);
startActivity(intent) ;
}
room1.xml
<menu xmlns:android="http://schemas.android.com/apk/res/android" >
<item
android:icon="@android:drawable/ic_menu_share"
android:title="Option 1"
android:id="@+id/menu_option_one"
/>
<item
android:icon="@android:drawable/ic_menu_preferences"
android:title="Option 2"
android:id="@+id/menu_option_two"
/>
<item
android:icon="@android:drawable/ic_menu_info_details"
android:title="Option 3"
android:id="@+id/menu_option_three"
/>
</menu>
here is mainfest
<application
android:allowBackup="true"
android:icon="@drawable/ic_launcher"
android:label="@string/app_name"
android:theme="@style/AppTheme" >
<activity
android:name="com.example.homeautomation.Splash"
android:label="@string/app_name"
android:screenOrientation="landscape"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
<activity
android:name="com.example.homeautomation.Main"
android:label="@string/title_activity_main"
android:screenOrientation="landscape"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >
</activity>
<activity
android:name="com.example.homeautomation.Room1"
android:label="@string/title_activity_room1"
android:screenOrientation="landscape"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >
</activity>
<activity
android:name="com.example.homeautomation.DemoMSG"
android:label="@string/title_activity_demo_msg"
android:screenOrientation="landscape"
android:theme="@android:style/Theme.NoTitleBar.Fullscreen" >
</activity>
<activity
android:name="com.example.homeautomation.SettingsActivity"
android:label="@string/title_activity_settings"
>
</activity>
</application>
log cat:
04-19 03:59:28.179: I/Choreographer(2733): Skipped 100 frames! The application may be doing too much work on its main thread.
04-19 03:59:32.849: D/Option(2733): 2
04-19 03:59:34.659: D/AndroidRuntime(2733): Shutting down VM
04-19 03:59:34.659: W/dalvikvm(2733): threadid=1: thread exiting with uncaught exception (group=0xb4a1eb90)
04-19 03:59:34.679: E/AndroidRuntime(2733): FATAL EXCEPTION: main
04-19 03:59:34.679: E/AndroidRuntime(2733): Process: com.example.homeautomation, PID: 2733
04-19 03:59:34.679: E/AndroidRuntime(2733): java.lang.RuntimeException: Unable to stop activity {com.example.homeautomation/com.example.homeautomation.Room1}: java.lang.NullPointerException
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3169)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.app.ActivityThread.handleStopActivity(ActivityThread.java:3215)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.app.ActivityThread.access$1000(ActivityThread.java:135)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1424)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.os.Handler.dispatchMessage(Handler.java:102)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.os.Looper.loop(Looper.java:137)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.app.ActivityThread.main(ActivityThread.java:4998)
04-19 03:59:34.679: E/AndroidRuntime(2733): at java.lang.reflect.Method.invokeNative(Native Method)
04-19 03:59:34.679: E/AndroidRuntime(2733): at java.lang.reflect.Method.invoke(Method.java:515)
04-19 03:59:34.679: E/AndroidRuntime(2733): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:777)
04-19 03:59:34.679: E/AndroidRuntime(2733): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:593)
04-19 03:59:34.679: E/AndroidRuntime(2733): at dalvik.system.NativeStart.main(Native Method)
04-19 03:59:34.679: E/AndroidRuntime(2733): Caused by: java.lang.NullPointerException
04-19 03:59:34.679: E/AndroidRuntime(2733): at com.example.homeautomation.Room1.onStop(Room1.java:183)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.app.Instrumentation.callActivityOnStop(Instrumentation.java:1212)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.app.Activity.performStop(Activity.java:5388)
04-19 03:59:34.679: E/AndroidRuntime(2733): at android.app.ActivityThread.performStopActivityInner(ActivityThread.java:3166)
04-19 03:59:34.679: E/AndroidRuntime(2733): ... 11 more
04-19 03:59:37.299: I/Process(2733): Sending signal. PID: 2733 SIG: 9
04-19 03:59:38.729: D/dalvikvm(2760): GC_FOR_ALLOC freed 35K, 4% free 2716K/2828K, paused 34ms, total 35ms
04-19 03:59:38.729: I/dalvikvm-heap(2760): Grow heap (frag case) to 3.192MB for 491416-byte allocation
04-19 03:59:38.779: D/dalvikvm(2760): GC_FOR_ALLOC freed <1K, 4% free 3195K/3308K, paused 42ms, total 42ms
04-19 03:59:38.999: D/gralloc_goldfish(2760): Emulator without GPU emulation detected.
回答1:
Caused by: java.lang.NullPointerException
04-19 03:59:34.679: E/AndroidRuntime(2733): at com.example.homeautomation.Room1.onStop(Room1.java:183)
Just set a breakpoint here (Room1.onStop) and find out what is null.
回答2:
Use something like this:
public boolean onOptionsItemSelected(MenuItem item) {
switch (item.getItemId()) {
case R.id.menu_option_two:
Intent intent = new Intent(this, SettingsActivity.class);
startActivity(intent);
return true;
}
return super.onOptionsItemSelected(item);
}
回答3:
While searching the web, I came across this, which is an alternative to what you`re trying to do.
You could have a base activity with 2 buttons( if you like ), one to take you to your main activity and another to take you to settings.
来源：https://stackoverflow.com/questions/23167647/starting-new-activity-from-onoptionsitemselected