why does the android os need to have apps running in the backround that are not ever selected

why cant an开发者_如何学Cdroid os be more like apple os on the the ituch/iphone? where the app doesn't run until it is selected. it is also closed; stays closed until it is opened again.

i think this would make the android phones run faster and more efficiently(battery would last longer).

1. A lot of Android apps (I think most of them) run exactly as you describe it - they have an activity that is closed or suspended as soon as you leave it - a suspended Activity only consumes memory and can be discarded in an instant. (iOS does nearly the same)
2. Even on the iPhone there are applications that run in the background, the most prominent example being Mobile Safari. The difference is that only Apple can write applications that run in the background without restriction, and that a regular user has no way of monitoring these background apps. (this has led to massive overcharging issues in the case of users leaving Mobile Safari on a page where streaming content was loaded.)
3. There are legitimate use cases where you need an app to continue running in the background (downloading, uploading, playing music, waiting for a VoIP call) - none of it was possible for a third-party to do it on the iPhone until iOS4, making applications such as Pandora or Skype nearly useless.
4. For good or ill, Apple consistently restricts what third-party developers are allowed to do on iOS devices (App Store policy, private APIs, specialized APIs for background tasks mentioned in point 3). On the other hand, Google seems to prefer that third-party Android developers have access to the same APIs as Google's Android app developers.
5. The biggest Android performance problem IMO is responsiveness, the fixing of which is a lot more involved than saying "no Apps in Background thx". (See http://android-developers.blogspot.com/2010/12/new-gingerbread-api-strictmode.html for more information)

An Android developer's blog explains the reasoning behind Android multitasking.

• We did not want to require that users close applications when "done" with them.
• Mobile devices … have fairly hard limits on memory use.

These competing constraints were a key motivation for Android's design.

The fact that you can see an application's process "running" does not mean the application is running or doing anything.

The articles linked from there also have interesting things to say on the subject

The RadioActive Yak:

When should your app include an exit button? The Short Answer: Never.

Wickenden:

One of the first things the naive but technically inquisitive new android user does is begin to wonder how all the things they are running should be “shut down”.

Google’s android system has been designed for multi-tasking in ways that allow programs to be ready to respond to a changed environmental condition instantly (an alarm to wake you, a notification that you have arrived at your destination and so forth) as well as actually “running” and consuming resources when needed. Additionally the android system itself is smart about how it deals with low memory conditions and is capable of completely blowing away applications in such a way that their state is remembered and can be restored when there is more memory. Task Killers (whose behavior is radically clipped in Android 2.2 “Froyo”) actually can cause harm by destroying a process that other apps need to function correctly.