Android：使用Parcerable将自定义对象的ArrayList从片段发送到活动

Question

I have a problem making this to work:

1) I have custom class that implements Parcelable:

public class CityCoordinates implements Parcelable {

private double latitude;
private double longitude;

public double getLatitude() {
    return latitude;
}

public void setLatitude(double latitude) {
    this.latitude = latitude;
}

public double getLongitude() {
    return longitude;
}

public void setLongitude(double longitude) {
    this.longitude = longitude;
}

public CityCoordinates(double latitude, double longitude) {
    this.latitude = latitude;
    this.longitude = longitude;
}

public CityCoordinates(Parcel in) {
    latitude = in.readDouble();
    longitude = in.readDouble();
}

public int describeContents() {
    return 0;
}

public void writeToParcel(Parcel dest, int flags) {
    dest.writeDouble(latitude);
    dest.writeDouble(longitude);
}

public static final Parcelable.Creator<CityCoordinates> CREATOR = new Parcelable.Creator<CityCoordinates>() {

    public CityCoordinates createFromParcel(Parcel in) {
        return new CityCoordinates(in);
    }

    public CityCoordinates[] newArray(int size) {
        return new CityCoordinates[size];
    }

};

}

2) I have a fragment with ArrayList listItems that I want to send to another activity:

ArrayList<CityCoordinates> listItems = new ArrayList<>();
...
Intent intent = new Intent(getActivity(), MapActivity.class);
            intent.putParcelableArrayListExtra("key", listItems);
            startActivity(intent);

3) This is how I retrieve ParcelableArrayListExtra in the activity I started:

public class MapActivity extends ActionBarActivity {
...
ArrayList<CityCoordinates> cityCoordinatesList = getIntent().getParcelableArrayListExtra("key");

But I get NullPointerException when I try to retrieve extra. What I am doing wrong? Thank you for your help!

Answer 1

In order to retreive extras from intent I should've done so inside onCreate of the activity.

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.fragment_map_main);
...
    ArrayList<CityCoordinates> cityCoordinatesList = getIntent().getParcelableArrayListExtra("key");
...

Answer 2

I would suggest define an interface and let the main activity implement it. Pass that reference to the fragment. when you want to send the data, just pass it through interface and remove the fragment. This will save some time