使用setText（）在TextView上发生NullPointerException

Question

I'm rather new to android programming, and am running into my old friend the NullPointerException ...

I've been on it for quite a while now, but can't figure out what is wrong.

basicly gives me a NullPointerException when I try to call any .setText() methods, maybe someone sees what I'm doing wrong here...(though i tried to follow examples as close as possible)

public class lessonView extends Activity {

TextView adressOfLecture;
TextView lecturer;
TextView lesson;

Lecture lecture;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_lesson_view);

    Bundle data = getIntent().getExtras();
    lecture = (Lecture) data.getParcelable("student");

    adressOfLecture = (TextView)findViewById(R.id.lectureViewAdressLabel);
    lecturer = (TextView)findViewById(R.id.lectureViewLecturerLabel);
    lesson = (TextView)findViewById(R.id.lectureViewTitle);

    updateLabels();

}


@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_lesson_view, 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);
}

private void updateLabels(){
    adressOfLecture.setText(lecture.getRoom());
    lecturer.setText(lecture.getTutor());
    lesson.setText(lecture.getName());
}

}

also, here's my xml file:

<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:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
android:paddingBottom="@dimen/activity_vertical_margin"
tools:context="com.coronarip7.app.stupla.lessonView">


<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="(ort)"
    android:id="@+id/lectureViewAdressLabel"
    android:layout_centerVertical="true"
    android:layout_toStartOf="@+id/lectureViewTitle"
    android:layout_marginRight="86dp" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="dozent"
    android:id="@+id/lectureViewLecturerLabel"
    android:layout_toEndOf="@+id/lectureViewTitle"
    android:layout_alignTop="@+id/lectureViewAdressLabel"
    android:layout_alignParentEnd="true"
    android:layout_marginRight="27dp" />

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:id="@+id/lectureViewTitle"
    android:gravity="center_horizontal"
    android:text="test"
    android:textSize="40dp"
    android:textStyle="bold"
    android:padding="10dp"
    android:layout_row="0"
    android:layout_column="0"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true" />

and the logcat I'm getting:

04-25 01:23:51.058  12236-12236/com.coronarip7.app.stupla E/AndroidRuntime﹕ FATAL EXCEPTION: main
Process: com.coronarip7.app.stupla, PID: 12236
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.coronarip7.app.stupla/com.coronarip7.app.stupla.lessonView}: java.lang.NullPointerException
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2215)
        at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
        at android.app.ActivityThread.access$800(ActivityThread.java:145)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
        at android.os.Handler.dispatchMessage(Handler.java:102)
        at android.os.Looper.loop(Looper.java:136)
        at android.app.ActivityThread.main(ActivityThread.java:5081)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:515)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:781)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
        at dalvik.system.NativeStart.main(Native Method)
 Caused by: java.lang.NullPointerException
        at com.coronarip7.app.stupla.lessonView.updateLabels(lessonView.java:59)
        at com.coronarip7.app.stupla.lessonView.onCreate(lessonView.java:31)
        at android.app.Activity.performCreate(Activity.java:5231)
        at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
        at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)
            at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2265)
            at android.app.ActivityThread.access$800(ActivityThread.java:145)
            at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
            at android.os.Handler.dispatchMessage(Handler.java:102)
            at android.os.Looper.loop(Looper.java:136)
            at android.app.ActivityThread.main(ActivityThread.java:5081)
            at java.lang.reflect.Method.invokeNative(Native Method)
            at java.lang.reflect.Method.invoke(Method.java:515)
            at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:781)
            at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
            at dalvik.system.NativeStart.main(Native Method)

seriously, I am out of ideas on how to fix it...

Answer 1

First check if you properly put the extra in the intent. Then I would use the following test in your onCreate method:

Intent intent = getIntent();
if (intent.hasExtra("student")){
    lecture = (Lecture) intent.getParcelableExtra("student");
}

Then test if lecture is null like Rami wrote earlier.

Answer 2

Ok guys, thanks for the suggestions, but I'll go the global route. I'll create a static version of my array (from which i wanted to pass an object via the Intent), and just pass an int[] array with the coordiantes and call it in the new view.

But thanks for the quick answers anyways!

(I'm new to stackoverflow, is there a way to mark a question as "solved", or "not-needed-to-be-solved-anymore"?)

Answer 3

Do not use static objects in your code like arrays, objects, they have globally available, you should create intent and add your data into your intent like and call your activity

Intent intent = new Intent ();
intent.putExtra ("student",value);

start activity with intent And in your lessonViewActivity check for intent like

Intent intent = getIntent();
if (intent.hasExtra("student")){
    lecture = (Lecture) intent.getParcelableExtra("student"); 
if (lecture !=null){
updateLabels ();
}
}