I have not used TabHost before, and following several tutorials to piece something together, but I keep getting a NullPointerException at my line 81 where I have my Resources class variable when using it to get an icon from a drawable using
TabSpec tabSpecVolcano = tabHost
.newTabSpec("Volcano") // Line 81
.setIndicator("", resrc.getDrawable(R.drawable.ic_tab_volcano))
.setContent(intentVolcano);
Line 81 is the "caused by" in my LogCat. This error is causing the emulator to crash without showing anything at startup. Below I will post my MainSelectorActivity.java, its xml, and the xml layout for the tab belonging to line 81, the Volcano layout (and class too). All other tabs have a very similar layout and class as the Volcano one. Plus I will post my LogCat. Let me know if you need to see other files. Thanks very much.
UPDATE: The original error was solved by instantiating the getResources() inside of the onCreate method. See below for the answer with an explanation of why it worked.
MainSelectorActivity.java
package com.azurespot.disastertimer.app;
import android.content.Intent;
import android.content.res.Resources;
import android.os.Bundle;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentTabHost;
import android.widget.TabHost.TabSpec;
public class MainSelectorActivity extends FragmentActivity {
Resources resrc = getResources();
FragmentTabHost tabHost;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main_selector);
// TabHost setup
tabHost = (android.support.v4.app.FragmentTabHost)findViewById(android.R.id.tabhost);
tabHost.setup(this, getSupportFragmentManager(), R.id.realtabcontent);
//------Zombie tab------
// Creates tab and sets zombie image in view
// tabHost.addTab(tabHost.newTabSpec("zombie").setIndicator("Zombie",
// getResources().getDrawable(R.drawable.ic_tab_zombie)),
// ZombieTab.class, null);
// When icon is clicked, zombie image shows
Intent intentZombie = new Intent().setClass(this, ZombieTab.class);
TabSpec tabSpecZombie = tabHost
.newTabSpec("Zombie")
.setIndicator("", resrc.getDrawable(R.drawable.ic_tab_zombie))
.setContent(intentZombie);
//------Nuclear tab------
// Creates tab and sets nuclear image in view
// tabHost.addTab(tabHost.newTabSpec("nuclear").setIndicator("Nuclear",
// getResources().getDrawable(R.drawable.ic_tab_nuclear)),
// NuclearTab.class, null);
// When icon is clicked nuclear image shows
Intent intentNuclear = new Intent().setClass(this, NuclearTab.class);
TabSpec tabSpecNuclear = tabHost
.newTabSpec("Nuclear")
.setIndicator("", resrc.getDrawable(R.drawable.ic_tab_nuclear))
.setContent(intentNuclear);
//------Tsunami tab------
// Creates tab and sets tsunami image in view
// tabHost.addTab(tabHost.newTabSpec("tsunami").setIndicator("Tsunami",
// getResources().getDrawable(R.drawable.ic_tab_tsunami)),
// TsunamiTab.class, null);
// When icon is clicked tsunami image shows
Intent intentTsunami = new Intent().setClass(this, TsunamiTab.class);
TabSpec tabSpecTsunami = tabHost
.newTabSpec("Tsunami")
.setIndicator("", resrc.getDrawable(R.drawable.ic_tab_tsunami))
.setContent(intentTsunami);
//------Godzilla tab------
// Creates tab and sets tsunami image in view
// tabHost.addTab(tabHost.newTabSpec("godzilla").setIndicator("Godzilla",
// getResources().getDrawable(R.drawable.ic_tab_godzilla)),
// GodzillaTab.class, null);
// When icon is clicked godzilla image shows
Intent intentGodzilla = new Intent().setClass(this, GodzillaTab.class);
TabSpec tabSpecGodzilla = tabHost
.newTabSpec("Godzilla")
.setIndicator("", resrc.getDrawable(R.drawable.ic_tab_godzilla))
.setContent(intentGodzilla);
//------Volcano tab------
// Creates tab and sets volcano image in view
// tabHost.addTab(tabHost.newTabSpec("volcano").setIndicator("Volcano",
// getResources().getDrawable(R.drawable.ic_tab_volcano)),
// VolcanoTab.class, null);
// When icon is clicked volcano image shows
Intent intentVolcano = new Intent().setClass(this, VolcanoTab.class);
TabSpec tabSpecVolcano = tabHost
.newTabSpec("Volcano")
.setIndicator("", resrc.getDrawable(R.drawable.ic_tab_volcano))
.setContent(intentVolcano);
// add all tabs
tabHost.addTab(tabSpecZombie);
tabHost.addTab(tabSpecNuclear);
tabHost.addTab(tabSpecTsunami);
tabHost.addTab(tabSpecGodzilla);
tabHost.addTab(tabSpecVolcano);
//set Zombie tab as default (zero based)
tabHost.setCurrentTab(0);
}
}
activity_main_selector.xml
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.azurespot.disastertimer.app.MainSelectorActivity">
<android.support.v4.app.FragmentTabHost
android:id="@android:id/tabhost"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<LinearLayout
android:orientation="vertical"
android:layout_width="match_parent"
android:layout_height="match_parent" >
<TabWidget
android:id="@android:id/tabs"
android:orientation="horizontal"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_weight="0" />
<FrameLayout
android:id="@android:id/tabcontent"
android:layout_width="0dp"
android:layout_height="0dp"
android:layout_weight="0" />
<FrameLayout
android:id="@+id/realtabcontent"
android:layout_width="match_parent"
android:layout_height="0dp"
android:layout_weight="1" />
</LinearLayout>
</android.support.v4.app.FragmentTabHost>
<LinearLayout
android:layout_width="match_parent"
android:layout_height="140dp"
android:orientation="horizontal"
android:layout_marginTop="200dp"
android:gravity="center_horizontal">
<NumberPicker
android:id="@+id/numberPicker1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="16dp"
android:layout_marginTop="20dp" />
<NumberPicker
android:id="@+id/numberPicker2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="14dp"
android:layout_marginTop="20dp" />
<NumberPicker
android:id="@+id/numberPicker3"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="14dp"
android:layout_marginTop="20dp" />
</LinearLayout>
</RelativeLayout>
VolcanoTab.java
package com.azurespot.disastertimer.app;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
/**
* Created by azuremoss on 4/22/14.
*/
public class VolcanoTab extends Fragment {
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
// Inflate the layout for this fragment
View v = inflater.inflate(R.layout.volcano_tab, container, false);
return v;
}
}
volcano_tab.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent">
<ImageButton
android:layout_width="match_parent"
android:layout_height="160dp"
android:layout_marginTop="0dp"
android:id="@+id/imageButton"
android:layout_gravity="center_horizontal"
android:src="@drawable/volcano_image"
android:text="@string/volcano_fragment_string"/>
</LinearLayout>
LogCat
1111-1111/com.azurespot.disastertimer.app E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.azurespot.disastertimer.app/com.azurespot.disastertimer.app.MainSelectorActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1983)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
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:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at android.content.ContextWrapper.getResources(ContextWrapper.java:81)
at com.azurespot.disastertimer.app.MainSelectorActivity.<init>(MainSelectorActivity.java:13)
at java.lang.Class.newInstanceImpl(Native Method)
at java.lang.Class.newInstance(Class.java:1319)
at android.app.Instrumentation.newActivity(Instrumentation.java:1053)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1974)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
at android.app.ActivityThread.access$600(ActivityThread.java:130)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:137)
at android.app.ActivityThread.main(ActivityThread.java:4745)
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:786)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
at dalvik.system.NativeStart.main(Native Method)
Actually your error is line 13 in MainSelectorActivity. Line 81 is where the null pointer exception occurs in ContextWrapper which originates from a call in line 13 in your activity class.
Line 13 is
Resources resrc = getResources();
Why are you getting an error here? Since you are calling getResources as a declaration, this call happens before the onCreate of your activity.
getResources requires a context which in this case is from your activity, however since the context has not been properly initialized yet, you will get a null pointer exception.
So if you still want to keep your global resrc variable, you will need to simply set it in the onCreate method.
Resources resrc;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
resrc = getResources();
...
}