什么参数应该传递给.show（）？

Question

So I'm pretty new to Android development, and Java programming in general (well, okay, so programming period...), so I came across something that I found the answer to online, but I want to know WHY it works.

I created a class that was concerned with creating an AlertDialog, based off of the code on that Android Tutorial website. Then, in a different activity, I created a method that instantiated an object of this AlertDialog class. Then, I tried to use .show() to actually call up the AlertDialog.

It wouldn't work without any arguments, so the two arguments I had to pass to it were getFragmentManager(), and any kind text, as long as it was in quotations, like this:

alertDialogObject.show(getFragmentManager(), "Hi");

Finally after writing it like this the errors went away, and the AlertDialog box popped uo in my app just fine. Can someone explain to me the basics of what I passed to show(), and what kind of arguments show() wants?

Thanks for the help!!!

Answer 1

Without a link to the tutorial you're referring to, I'm going to assume you're talking about the implementation of a DialogFragment , based on the code snippet:

alertDialogObject.show(getFragmentManager(), "Hi");

For the best answer to your question as to "what I passed to show() " and "what kind of arguments show() wants " , you should probably refer to the documentation on the DialogFragment class .

To answer the second question more specifically, have a look at the two available show(...) methods. These are called 'overloads' in Java terminology by the way: methods that have the same name, but accept different parameters. In the documentation, every method usually has short description explaining what it does, what its return value is and what parameters are expected. No exception for these two:

public int show(FragmentTransaction transaction, String tag)

Display the dialog, adding the fragment using an existing transaction and then committing the transaction.

public void show(FragmentManager manager, String tag)

Display the dialog, adding the fragment to the given FragmentManager. This is a convenience for explicitly creating a transaction, adding the fragment to it with the given tag, and committing it. This does not add the transaction to the back stack. When the fragment is dismissed, a new transaction will be executed to remove it from the activity.

So you have the option of calling .show(...) either with a FragmentTransaction or FragmentManager , followed by a tag. There is a plethora of resources on the way how to work with transactions and/or the manager out there. If you like to know more about that, I suggest you start with any tutorial or Android book that explains the concepts of (and differences between) activities and fragments. If it's examples you're after, definitely go through the API demos that come with the Android SDK.