Android Universal App Approach

问题:

I want to develop an universal app . I am novice to this approach .That means a single apk for both tablet and phone application . I had go through

Support Library

Fragments

My aim is to build different UI for Tablet and Phone inside a single APk .

I had read Getting Your App Ready for Jelly Bean and Nexus 7 . This article mention that

res/layout/activity_home.xml

To take advantage of the extra space on the 7” screen you might provide an alternative layout:

res/layout-sw600dp/activity_home.xml

The sw600dp qualifier declares that these resources are for devices that have a screen with at least 600dp available on its smallest side. 

    Furthermore you might even provide a different layout for 10” tablets:

res/layout-sw720dp/activity_home.xml

That means we can use different layout for different device . This confuses me

EDIT 1 :: Scenario

Suppose

if my phone UI layout contains one-view pager and 

tablet UI layout contain two-view pager  . 

How can we achieve this ?? In this article it says that you an designe different layout with same name for different screen and keep it corresponding folder . But my doubt will this arise exceptions if it try to initialize widget component of Tablet layout when app is running in a phone .

EDIT 2 : The idea came into my mind is determine which type of device is i am using ie Tab or phone .

Determine if the device is a smartphone or tablet?

Then avoid the initialization of widgets if app is phone . Is there any better way than this ??

EDIT 3 : My application support from 2.3 to higher versions

If my layouts for tablet holds additional widgets compared to phone layout .How an i initialize and use . Hope all understood my need . So please clarify my doubt

回答1:

When I face the problem, I create following structure.

res/layout
res/layout-sw600dp

then to distinguish values and other resources,

res/values
res/values-sw600dp
res/values-sw720dp

You noticed that there is only one layout directory and two values directory to specify margins and paddings and other resources. So single layout can be used for 7" as well 10" tablet. This is my scenario, you can also define layout-sw720dp. I did that due to reduce compilation time of layouts.

I have also different layouts in phone and tablet. For example, I have a ListView in first screen, then when user click on item, it will open other activity and there is DetailView for that. But in tablet, I have left side ListView and right side DetailView.

So to do so, in values/strings, I place following code,

<bool name="isTablet">false</bool>

and same for tablet values-sw600dp/strings

<bool name="isTablet">true</bool>

Now, come to part of coding. I have a splash screen and which has common layout. So it will display common screen. But when user click on any button, it will check whether it is tablet or not. To check it,

boolean isTablet = getResources().getBoolean(R.bool.isTablet);

You have now flag indicate whether your application is running on phone or tablet.

I have created two packages,

com.phone
com.tablet

then as per flag, I direct my activity to phone package and tablet package.

Example,

if(isTablet)
    startActivity(this,TabXYZ.class);
else
    startActivity(this,PhXYZ.class);

And this approach has solved my problem.

回答2:

findViewById will return the widget in case it's present in the layout, null in case there's no such widget. So if it returns non-null you can proceed with further initialization.