在不丢失父活动的情况下打开新活动

Question

I have a DetailsActivity that lists several thumbnails of images. I want to open a new activity, by passing in the URL as a string, to a " FullScreenActivity " that allows the user to see the larger version of the image.

The DetailsActivity contains a complex data object that I don't want to loose when the user opens the full screen view.

I can pass the string to the new " FullScreenActivity ", the image downloads, and I can pinch/zoom the images etc.. but when I click the UP button to return to the DetailsAcitivity , the app crashes because the complex data object is gone.

How do I keep the DetailsActivity around while the user is looking at a bigger image?

Here is how I call the FullScreenActivity. This is called in a for loop that creates a new image view and add it to the activity.

image.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent(DetailsActivity.this, ViewFullPhotoActivity.class);
intent.putExtra("FullScreenPicture", (String) finalImageMap.get("MainImage"));
startActivity(intent);
}
});

And in my FullScreenActivity , I get the URL string via

String fullScreenImage = (String) getIntent().getCharSequenceExtra("FullScreenPicture");

I toyed with the idea of packaging up the complex data object and sending it along with the new intent, but surely that isn't a best practice. There are other things that would not be great for the user if I went that path, specifically re downloading all the thumbnails, or loosing data entered into a form.

Answer 1

I would suggest to override onSaveInstanceState() , save your data there and inside onCreate() get your saved data from savedInstanceState . See the documentation for more.

@Override
public void onSaveInstanceState(Bundle savedInstanceState) {
    super.onSaveInstanceState(savedInstanceState);
    // Save your data here with savedInstanceState.put<something>...
}

If your data is complex (not a string or int or some simple type), you can write a method for saving it to a Bundle (what can be put in the savedInstanceState bundle), and another one which parses a bundle and restores your data from it). But it is not a good idea storing images like this... you could cache them on sdcard (eg in the data directory of your app, but not in the memory).

Another option to show the contents of your " FullScreenActivity " in a full screen dialog instead an activity, so the DetailsActivity won't be destroyed in the background.

Answer 2

If your complex data structure cannot be saved using onSaveInstanceState , then the easiest method is to save it in a Singleton object and then keep the complex object in memory. You can find an example here .

However, it's not the best approach. You might encounter unexpected NULL pointer exceptions if you assume that the complex object will be in memory all the time. If you want to go further, then you can either

• Serialize the object and save it to disk
• Use a SQLite database and save it in the DB

I believe the latter 2 methods are better, but require some significant work depending on how complex your data structure is.

Answer 3

This will do. Inside Your Manifest file.

 <activity
            android:name=".FullScreenActivity"
            android:label="FullScreenActivity"
            android:launchMode="singleTop"
            android:parentActivityName=".DetailsActivity">

This will specify your fullscreen Activity will be the child of DetailsActivity. so this will open the Fullscreen activity on Top of DetailsActivity.

Answer 4

I found a much simpler solution. In my android manifest, in my DetailsActivity I simply added android:launchMode="singleTop" . That did the trick.