问题描述
How can I pass an object of a custom type from one Activity to another using the
putExtra()
method of the class Intent?
If you're just passing objects around then Parcelable was designed for this. It requires a little more effort to use than using Java's native serialization, but it's way faster (and I mean way, WAY faster).
From the docs, a simple example for how to implement is:
// simple class that just has one member property as an example
public class MyParcelable implements Parcelable {
private int mData;
/* everything below here is for implementing Parcelable */
// 99.9% of the time you can just ignore this
@Override
public int describeContents() {
return 0;
}
// write your object's data to the passed-in Parcel
@Override
public void writeToParcel(Parcel out, int flags) {
out.writeInt(mData);
}
// this is used to regenerate your object. All Parcelables must have a CREATOR that implements these two methods
public static final Parcelable.Creator<MyParcelable> CREATOR = new Parcelable.Creator<MyParcelable>() {
public MyParcelable createFromParcel(Parcel in) {
return new MyParcelable(in);
}
public MyParcelable[] newArray(int size) {
return new MyParcelable[size];
}
};
// example constructor that takes a Parcel and gives you an object populated with it's values
private MyParcelable(Parcel in) {
mData = in.readInt();
}
}
Observe that in the case you have more than one field to retrieve from a given Parcel, you must do this in the same order you put them in (that is, in a FIFO approach).
Once you have your objects implement Parcelable
it's just a matter of putting them into your Intents with putExtra():
Intent i = new Intent();
i.putExtra("name_of_extra", myParcelableObject);
Then you can pull them back out with getParcelableExtra():
Intent i = getIntent();
MyParcelable myParcelableObject = (MyParcelable) i.getParcelableExtra("name_of_extra");
If your Object Class implements Parcelable and Serializable then make sure you do cast to one of the following:
i.putExtra("parcelable_extra", (Parcelable) myParcelableObject);
i.putExtra("serializable_extra", (Serializable) myParcelableObject);
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