Question

In my project I have a model which holds basic information about model. For example lets say that the model is a Car. Then there are many different varieties of Cars and these have different data assigned to them. All models must be parcelables.

The differences between different cars is very small, it might just be a few data fields. So this is solved by creating presenters (just a class that holds data) for the different cars. The presenter would then know which extra data it should hold. Because the the presenter itself is not parcelable it will have a Bundle for all its data which then the Car class will then add to the parcelable. I don’t want to make the presenters into parcelables.

So Car takes the Bundle from the presenter and puts it in its parcel:

  public void writeToParcel(Parcel parcel, int flags) {
    parcel.writeBundle(getPresenter().getBundle());
  } 

And it will then unpack it with:

  public Car(Parcel parcel) {    
    getPresenter().setBundle(parcel.readBundle());
  }

This works fine until a parcelable object is added to the bundle by the presenter.
Then I get this error:

11-16 15:06:37.255: E/AndroidRuntime(15193): FATAL EXCEPTION: main
11-16 15:06:37.255: E/AndroidRuntime(15193): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example/com.example.activity}: android.os.BadParcelableException: ClassNotFoundException when unmarshalling: com.example.model.engine
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2185)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2210)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.app.ActivityThread.access$600(ActivityThread.java:142)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1208)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.os.Handler.dispatchMessage(Handler.java:99)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.os.Looper.loop(Looper.java:137)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.app.ActivityThread.main(ActivityThread.java:4931)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at java.lang.reflect.Method.invokeNative(Native Method)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at java.lang.reflect.Method.invoke(Method.java:511)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:791)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:558)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at dalvik.system.NativeStart.main(Native Method)
11-16 15:06:37.255: E/AndroidRuntime(15193): Caused by: android.os.BadParcelableException: ClassNotFoundException when unmarshalling: com.example.model.engine
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.os.Parcel.readParcelable(Parcel.java:2077)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.os.Parcel.readValue(Parcel.java:1965)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.os.Parcel.readMapInternal(Parcel.java:2226)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.os.Bundle.unparcel(Bundle.java:223)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at android.os.Bundle.getString(Bundle.java:1055)
11-16 15:06:37.255: E/AndroidRuntime(15193):         at com.example.cars.CarPresenter.getExtraString(CarPresenter.java:34)
11-16 15:06:37.255: E/AndroidRuntime(15193):         ... 11 more

So it somehow fails to read anything from the Bundle.

This can be solved by modifying the readBundle call to:

  public Car(Parcel parcel) {    
    getPresenter().setBundle(parcel.readBundle(engine.class.getClassLoader()));
  }

However, wouldn’t this mean that I could only have one type of parcelables in my bundle? For example, what if another presenter wanted to add another parcelable object to the bundle?

Could anyone shed some light on this?

Answer 1

You wrote in a comment:

However, my question was ment to be more of why do I even have to specify a class loader in this case

Dianne Hackborn, Android framework engineer, writes that:

when the bundle reads from the parcel it just extracts the data. It doesn’t actually unparcel from that data until later when you retrieve stuff from the bundle.

In the Bundle source code, we see that the setClassLoader()method sets the field mClassLoader:

public void setClassLoader(ClassLoader loader) {
     mClassLoader = loader;
 }

If we don’t use setClassLoader() or the constructor Bundle(ClassLoader loader),the mClassLoader field will be set to the default ClassLoader:

public Bundle(int capacity) {
     //...
     mClassLoader = getClass().getClassLoader();
 }

mClassLoader is then used to unmarshal the parcelled data in the unparcel() method:

 mParcelledData.readMapInternal(mMap, N, mClassLoader);
 mParcelledData.recycle();
 mParcelledData = null;

Net, if you don’t set the ClassLoader it will default to the system ClassLoader when unmarshalling its parcelled data, and we’ll get a ClassNotFoundException when unmarshalling our custom Parcelable object data,