Android Bundle and ClassCastException

Question

I have two helper methods inside a custom View which are called by their Fragment:

public Bundle returnInstanceState() {
        Bundle state = new Bundle();
        state.putSerializable("colorData", colorData);
        return state;
}

public void loadInstanceState(Bundle savedInstanceState) {
    if(savedInstanceState.getSerializable("colorData") != null)
            colorData = (int[][]) savedInstanceState.getSerializable("colorData");
}

The lifecycle of colordata:

private int[][] colorData;

protected void onSizeChanged (int w, int h, int oldw, int oldh) 
{
    width = w;
    height = h;
    screen = new int[width*height];
    cellSize = 0;
    if(firstLoad && h!= 0 && w!=0)
    {

    if(nWidth>nHeight)
        colorData = new int[nWidth/(nHeight/170 - 1) + 1][170];
    else
            colorData = new int[nHeight/(nWidth/170 - 1) + 1][170];
        firstLoad = false;
    }
}

nWidth and nHeight are static int which represent the native resolution.

However once in a blue moon I am given a ClassCastException. Why?

From my tests it seems you can cast null to int[][] though thats not actually a goal of mine. colorData is type int[][] and I never get a NullPointerException anywhere so as far as I can tell everything works except the act of casting Serializable to int[][] and only occasionally.

Here is a stack trace, though it isn't of much use in this case:

java.lang.RuntimeException: Unable to start activity ComponentInfo{<MYPACKAGENAMEHERE>/<MYPACKAGENAMEHERE>.MusicVisualizerActivity}: java.lang.ClassCastException: [Ljava.lang.Object;
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1659)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1675)
    at android.app.ActivityThread.access$1500(ActivityThread.java:121)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:943)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:130)
    at android.app.ActivityThread.main(ActivityThread.java:3701)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:507)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:624)
    at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.ClassCastException: [Ljava.lang.Object;
    at <MYPACKAGENAMEHERE>.Visualization_Spectral$RenderView.loadInstanceState(Visualization_Spectral.java:95)
    at <MYPACKAGENAMEHERE>.Visualization_Spectral.onCreateView(Visualization_Spectral.java:46)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:870)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1080)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
    at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1810)
    at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:501)
    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129)
    at android.app.Activity.performStart(Activity.java:3791)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1632)
    ... 11 more
java.lang.ClassCastException: [Ljava.lang.Object;
    at <MYPACKAGENAMEHERE>.Visualization_Spectral$RenderView.loadInstanceState(Visualization_Spectral.java:95)
    at <MYPACKAGENAMEHERE>.visualization.Visualization_Spectral.onCreateView(Visualization_Spectral.java:46)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:870)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1080)
    at android.support.v4.app.FragmentManagerImpl.moveToState(FragmentManager.java:1062)
    at android.support.v4.app.FragmentManagerImpl.dispatchActivityCreated(FragmentManager.java:1810)
    at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:501)
    at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1129)
    at android.app.Activity.performStart(Activity.java:3791)
    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1632)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1675)
    at android.app.ActivityThread.access$1500(ActivityThread.java:121)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:943)
    at android.os.Handler.dispatchMessage(Handler.java:99)
    at android.os.Looper.loop(Looper.java:130)
    at android.app.ActivityThread.main(ActivityThread.java:3701)
    at java.lang.reflect.Method.invokeNative(Native Method)
    at java.lang.reflect.Method.invoke(Method.java:507)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:866)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:624)
    at dalvik.system.NativeStart.main(Native Method)

Answer 1

The Serializable interface if full of flaws and should be avoided whenever possible, especially in Android. From the looks of your code, your are only temporarily passing this object into a Bundle so an Activity or other component can be recreated and, if nothing else, serializing the object will provide poor performance for such a temporary need.

The API onRetainNonConfigurationInstance() and its counterpart getLastNonConfigurationInstance() will be a much more efficient method of passing that object around if you are in the context of an Activity . If you are using the Fragment APIs, take a look at the setRetainInstance() method as well.

HTH

Answer 2

For me it looks strange because Java (multidimensional) arrays are serializable by default (or am I wrong?). But it seems that, at least in Android, something is different with this.

You anyways should pass using Parcelable. It's somewhat tedious to implement, but faster than Serializable... Here is a howto: Passing multidimensional array using Serializable