I'm new to Android programming. I honestly can say, I have been searching for answers just about everywhere on the web. Please help.
Here is a stackoverflow link of a typical, and the nearest to what I want to achieve Change TextView text
My main problem is. Whenever I want to change the text of TextView object, I get a runtime error and the app is "force close". I am experience in OOP in C++ and PHP. I simply don't understand why the app terminate on textView.setText(message). Everything is defined. I even tried textView.setText("Hello"). whenever I remove this statement, the app run.
activity_main.xml (entire file)
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:id="@+id/container"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="MyApp.MainActivity"
tools:ignore="MergeRootFrame" />
fragment_main.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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context="MyApp.MainActivity$PlaceholderFragment" >
<TextView
android:id="@+id/hello_world"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@string/hello_world" />
</RelativeLayout>
MainActivity.java
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
String message = "hi there";
TextView textView = (TextView) findViewById(R.id.hello_world);
textView.setText("this is a test");
if (savedInstanceState == null) {
getSupportFragmentManager().beginTransaction()
.add(R.id.container, new PlaceholderFragment()).commit();
} // if
} // onCreate
// SKIPPED A FEW CODE
/**
* A placeholder fragment containing a simple view.
*/
public static class PlaceholderFragment extends Fragment {
public PlaceholderFragment() {
}
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
Bundle savedInstanceState) {
View rootView = inflater.inflate(R.layout.fragment_main, container,
false);
return rootView;
} // onCreateView
} // PlaceholderFragment
LogCat
06-23 20:11:42.106: W/dalvikvm(332): threadid=1: thread exiting with uncaught exception (group=0x40015560)
06-23 20:11:42.116: E/AndroidRuntime(332): FATAL EXCEPTION: main
06-23 20:11:42.116: E/AndroidRuntime(332): java.lang.RuntimeException: Unable to start activity ComponentInfo{MyApp/MyApp.MainActivity}: java.lang.NullPointerException
06-23 20:11:42.116: E/AndroidRuntime(332): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1647)
06-23 20:11:42.116: E/AndroidRuntime(332): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
06-23 20:11:42.116: E/AndroidRuntime(332): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
06-23 20:11:42.116: E/AndroidRuntime(332): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:931)
06-23 20:11:42.116: E/AndroidRuntime(332): at android.os.Handler.dispatchMessage(Handler.java:99)
06-23 20:11:42.116: E/AndroidRuntime(332): at android.os.Looper.loop(Looper.java:123)
06-23 20:11:42.116: E/AndroidRuntime(332): at android.app.ActivityThread.main(ActivityThread.java:3683)
06-23 20:11:42.116: E/AndroidRuntime(332): at java.lang.reflect.Method.invokeNative(Native Method)
06-23 20:11:42.116: E/AndroidRuntime(332): at java.lang.reflect.Method.invoke(Method.java:507)
06-23 20:11:42.116: E/AndroidRuntime(332): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
06-23 20:11:42.116: E/AndroidRuntime(332): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
06-23 20:11:42.116: E/AndroidRuntime(332): at dalvik.system.NativeStart.main(Native Method)
06-23 20:11:42.116: E/AndroidRuntime(332): Caused by: java.lang.NullPointerException
06-23 20:11:42.116: E/AndroidRuntime(332): at MyApp.MainActivity.onCreate(MainActivity.java:30)
06-23 20:11:42.116: E/AndroidRuntime(332): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
06-23 20:11:42.116: E/AndroidRuntime(332): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
06-23 20:11:42.116: E/AndroidRuntime(332): ... 11 more
06-23 20:11:44.826: I/Process(332): Sending signal. PID: 332 SIG: 9
What is NullPointerException and uncaught exception?
Again, the app runs when I remove the setText() line, byt terminates when included.
What am I doing wrong?
