Question

I try to save some data in internal storage on android but I keep getting a NullPointerException I think it has to do with the getFilesDir() I’m using but I’m not sure. Can Some Please help clarify if that is that case and help me write this file to the device. Here the Error message im am getting

01-20 22:11:59.020: E/AndroidRuntime(329): FATAL EXCEPTION: main
01-20 22:11:59.020: E/AndroidRuntime(329): java.lang.NullPointerException

01-20 22:11:59.020: E/AndroidRuntime(329):  at android.content.ContextWrapper.getFilesDir(ContextWrapper.java:178)

01-20 22:11:59.020: E/AndroidRuntime(329):  at yantz.imageapp4.main.writeElement(main.java:89)

01-20 22:11:59.020: E/AndroidRuntime(329):  at yantz.imageapp4.Panel.onTouchEvent(Panel.java:102)

---

Here is the oncreate of the main class

   public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
   FrameLayout sv = new FrameLayout(this);
    LinearLayout ll = new LinearLayout(this);
     test = new Panel(this);
    test.settest(1)   ;   
    ll.setOrientation(LinearLayout.VERTICAL);
    sv.addView(test);
    sv.addView(ll);
    setContentView(sv);}

---

Here my OnTouch method in the panel class

public boolean onTouchEvent(MotionEvent event) {
    mainactivity=new main();    
    mainactivity.writeElement(new Element(getResources(),(int) event.getX(),(int)  event.getY()));
        Log.v("Gesture", "is 1 ");   
        return super.onTouchEvent(event);
 }

---

Here is my writeObject method inside my main class

public void writeElement(Element obj){
    Log.v("main", "made it to method writeElement" );
    File f = new File(getFilesDir()+FILENAME);
    try {
fos = new FileOutputStream(f);
    ObjectOutputStream objectwrite = new ObjectOutputStream(fos);
    objectwrite.writeObject(obj);
 fos.close(); 
 Log.v("main", "file was  made File ");

 }catch (FileNotFoundException e){
    e.printStackTrace();
    Log.v("main", "file was not made File not found ");
 } catch (IOException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
    Log.v("main", "file was not made File IOException ");
}
}

---

manifest

<uses-sdk android:minSdkVersion="10" />

<application
    android:icon="@drawable/ic_launcher"
    android:label="@string/app_name" >
    <activity
        android:label="@string/app_name"
        android:name="yantz.imageapp4.main" >
        <intent-filter >
            <action android:name="android.intent.action.MAIN" />

            <category android:name="android.intent.category.LAUNCHER" />
        </intent-filter>
    </activity>

        <activity android:name=".charactors" android:label="@string/app_name"
        android:theme="@android:style/Theme.Black">
        <intent-filter>
    <action android:name="yantz.imageapp4.charactors" />
    <category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
    </activity>
<activity android:name=".main2" android:label="@string/app_name"
        android:theme="@android:style/Theme.Black">
        <intent-filter>
<action android:name="yantz.imageapp4.main2" />
<category android:name="android.intent.category.DEFAULT" />
        </intent-filter>
    </activity>
 </application>

</manifest>

Answer 1

I know what’s wrong. You can’t just write

mainactivity=new main();

getFilesDir should get the correct context instance but it doesn’t now.
Try something like that:

public boolean onTouchEvent(MotionEvent event) {
    main.writeElement(new Element(...), this.getContext);
    return super.onTouchEvent(event);
}

public static void writeElement(Element obj, Context context){
    ...
    File f = new File(context.getFilesDir(), FILENAME);
    ...
}