Dialog.show() vs. Activity.showDialog()

As far as I can tell, there are two ways to show a Dialog from an Activity.

1. Create the Dialog (for example, using an AlertDialog.Builder), and then call the newly created Dialog's show() method.
2. Call the Activity's showDialog() method, passing in an int that uniquely defines what sort of Dialog you want to build. Then override onCreateDialog() to actually build the Dialog, and Android will display it for you.

The second method seems to be the standard practice but I'm curious if there is any reason it matters which one I use. Here's all I can come up with:

Reasons to use Dialog.show

1. If you need to parameterize the Dialog in some way, it can be a little awkward to use Activity.showDialog, as described in this question. You may have to store a String or something in a member variable, just so that it can be retrieved moments later during onCreateDialog or onPr开发者_C百科epareDialog.
2. The logic for creating and modifying the dialog is spread out across a number of places, potentially making the code harder to read and maintain:
   • The place where you call showDialog()
   • Inside a potentially large switch statement in the overridden onCreateDialog method
   • Inside a potentially large switch statement in the overridden onPrepareDialog method

Reasons to use Activity.showDialog:

1. The API docs for Activity.showDialog say that the Dialog is "managed" by the Activity which I suppose provides some benefit? But this is also true if you use the AlertDialog.Builder, I would think, because you pass in this as an argument to the Builder's constructor.
2. If your Activity is going to show the same (or a very similar) Dialog several times, this option creates it only once, instead of creating a new one each time, thus putting less strain on the system as far as allocating space for new objects, garbage collection, etc.

So my question is, what are the criteria for deciding when to use Activity.showDialog and when to use Dialog.show, and why?

In my opinion you should prefer showDialog because this method will do most of the work for you. In example You don't have to worry that you will lose reference to your dialog after changing screen orientation. It will be recreated automatically. Dialog.show is much more prone to errors.

So I suggest you to use showDialog everywhere you can.

I think the decision is up to you, depending on the good reasons you have pointed out. If I have an activity which has just one dialog (say, for displaying an alert) I'd just fire the Dialog.show method... on the other hand, if the UI of my app relies too much of its functionality on the use of dialogs it'd be much better to use showDialog(). I think the best advantage of using showDialog() is that it's easier to read:

final int ERROR_DIALOG = 404;
final int MSG_DIALOG = 200;

.....

// if someone else read this, he/she will immediately understand what's going on
showDialog( ERROR_DIALOG );

You can use the overloaded method showDialog(int, Bundle) introduced in API level 8.
Simple shove the message to be shown into the bundle, which will be available in onPrepareDialog(int, Dialog, Bundle).

Yes, I know that showDialog() itself has been deprecated now.