活动和布局之间的联系？ 如何更改布局？ 如何开始和破坏活动？

Question

I'm a total beginner with Android and Eclipse and I have few questions that will help me understand the philosophy of Android:

1. The activity does all the work "behind the scenes". Activities are connected to a layout in the XML file. When the activity is started, if declared in setContentView method, the connected layout will be shown. Activity can be independent, without any layout, it can be invoked by another activity and will do all the work without showing any layout. Activity is something like a php file which is invoked by my submit button in HTML, and the layout is .HTML which shows elements.

Am I right with this one?

2. For example, if I want to change the layout of my app, I want to show Layout2.xml when clicking button in Layout1.xml . Then I have to destroy the activity which is connected with Layout1.xml and start the activity which is connected with Layout2.xml ? Is this correct? Is there any better way to do this?

3. How can I (by which method) destroy/stop a certain activity?

Thank you in an advance.

Answer 1

The best bet is to read the Android documentation regarding activites at http://developer.android.com/reference/android/app/Activity.html

I will answer your specific questions here though

1. An Activity is a window that the user can see (or a hidden window if there is no layout defined). It deals with the logic of a part of the app that the user can see and interact with. If we take the MVC model (Model View Controller), the Activity is the controller, in terms of it controls which data from the Model is shown on the View (the xml layout).

2. If you want to show a new window/screen/activity you do not need to destroy the current one. You can open a new activity whilst keeping the old one in the background (in the back stack). With the use of fragments, you can have multiple fragments in an activity so rather than changing activities, you can change fragments in a single activity. For more information about fragments take a look at http://developer.android.com/reference/android/app/Fragment.html .

3. This point relies heavily on the activity lifecycle. When an activity is destroyed, it means it is finishing and this can be done by the user pressing the back button whilst on the activity, the activity calling finish() on itself or by the Android operating system destroying the activity because memory is required elsewhere (this can happen when the app is in the background).

When we say an activity is stopped, it means that the activity is no longer visible to the user. This can be the case where the activity is in the back stack (another activity is in front of it) or if the app has been put into the background.

This is a brief answer to your questions but I highly recommend you read the Android documentation to gain better knowledge.