Question

I have my main activity which saves and load some data from the SharedPreferences… I’ve been able to do this until now.

These are my onCreate, onPause and OnResume methods.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    setTitle(R.string.title_activity_main);

    this.spinner = (Spinner) findViewById(R.id.geomObject);
    this.sbWidth = (SeekBar) findViewById(R.id.widthSB);
    this.sbDepth = (SeekBar) findViewById(R.id.depthSB);
    this.sbHeight = (SeekBar) findViewById(R.id.heightSB);
    this.widthProgress = (TextView) findViewById(R.id.widthDisplay);
    this.depthProgress = (TextView) findViewById(R.id.depthDisplay);
    this.heightProgress = (TextView) findViewById(R.id.heightDisplay);

    ...more code...
}

protected void onResume() {
    super.onResume();
    loadPrefs();
}

protected void onPause() {
    super.onPause();
    savePrefs();
}

And these are the method I do most of the work, so I can keep the onX methods clean:

private void savePrefs() {
    this.width = this.sbWidth.getProgress();
    this.depth = this.sbDepth.getProgress();
    this.height = this.sbHeight.getProgress();
    this.forma = this.spinner.getSelectedItemPosition();

    getSharedPreferences("SEEKBARS", MODE_PRIVATE).edit().putInt("width", width).commit();
    getSharedPreferences("SEEKBARS", MODE_PRIVATE).edit().putInt("depth", depth).commit();
    getSharedPreferences("SEEKBARS", MODE_PRIVATE).edit().putInt("height", height).commit();
    getSharedPreferences("SEEKBARS", MODE_PRIVATE).edit().putInt("forma", forma).commit();
    getSharedPreferences("LOCKBARS", MODE_PRIVATE).edit().putBoolean("lockbars", menuLock.isChecked()).commit();
}

private void loadPrefs() {
    int savedSpinner = getSharedPreferences("SEEKBARS", MODE_PRIVATE).getInt("forma", SPINNER_DEFAULT);
    int savedWidth = getSharedPreferences("SEEKBARS", MODE_PRIVATE).getInt("width", SEEKBAR_DEFAULT);
    int savedDepth = getSharedPreferences("SEEKBARS", MODE_PRIVATE).getInt("depth", SEEKBAR_DEFAULT);
    int savedHeight = getSharedPreferences("SEEKBARS", MODE_PRIVATE).getInt("height", SEEKBAR_DEFAULT);

    boolean savedLockFlag = getSharedPreferences("LOCKBARS", MODE_PRIVATE).getBoolean("lockbars", false);

    this.spinner.setSelection(savedSpinner);
    this.sbWidth.setProgress(savedWidth);
    this.sbDepth.setProgress(savedDepth);
    this.sbHeight.setProgress(savedHeight);
//This is the line raising the exception Display:
        this.menuLock.setChecked(savedLockFlag); 


        this.widthProgress.setText(String.valueOf(savedWidth) + " " + getResources().getString(R.string.blocks));
        this.depthProgress.setText(String.valueOf(savedDepth) + " " + getResources().getString(R.string.blocks));
        this.heightProgress.setText(String.valueOf(savedHeight) + " " + getResources().getString(R.string.blocks));
    }

I don’t see where is the error. I’ve been searching and I know that I can’t call getSharedPreferences on onCreate, that’s why I do it on onResume. What’s wrong?

I also attach the logcat, just in case:

FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to resume activity {es.nirvash.android.msg/es.nirvash.android.msg.MainActivity}: java.lang.NullPointerException
    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2567)
    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2595)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2109)
    at android.app.ActivityThread.access$600(ActivityThread.java:132)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1157)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:137)
    at android.app.ActivityThread.main(ActivityThread.java:4575)
    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:789)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:556)
    at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
    at es.nirvash.android.msg.MainActivity.loadPrefs(MainActivity.java:231)
    at es.nirvash.android.msg.MainActivity.onResume(MainActivity.java:147)
    at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1154)
    at android.app.Activity.performResume(Activity.java:4539)
    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2557)
    ... 12 more

Answer 1

The problem isn’t your boolean, it’s the variable menuLock. boolean (primitive type) cannot be null.

Find where menuLock is declared and make sure it has something to hold on to. That way, it will not be null when you use it. Of course, if it is a View, assign it something to hold on to in onCreate(), after setContentView(), since that’s has the Activity layout and creating guaranteed.