Develop Reference

Android: Is there any specific place on the document to find explicit XML reference?

Android documentation for XML is too hard to find. Whatever I get is all Java related documents. I am a newbie to Android and trying to find XML references for Views and Widgets. For now, I am searching for Checkbox but it I am struggling to get XML reference every time for any component.
Can anyone help me to learn how to find and use the reference documents especially for XML and its attributes?
Million thanks.

The XML attributes are referred;
The CheckBox is created from inheriting CompoundButton, TextView etc.
Each view has its own XML attributes. So for CheckBox all the inherited values are applicable. For instance ChackBox has Button bahaviour, TextBox behaviour etc. Hence all above apply for the CheckBox. So if you want to add Button related behavior of CheckBox refer above 'Button Attributes'. If you want to add Text related behavior of CheckBox refer above 'TextView Attributes' etc.
Also refer https://developer.android.com/reference/android/R.styleable
Sample layout xml as follows;
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical">
<LinearLayout android:id="#+id/llMainFill"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:gravity="bottom"
android:orientation="vertical">
<ListView android:id="#+id/lvLog"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:visibility="invisible" />
</LinearLayout>
</LinearLayout>

Reuse a group of buttons across several fragments

I have a fragment defined by the following xml file:
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="#+id/fragment_example"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent" >
<ImageButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="#drawable/ic_example"/>
</RelativeLayout>
Now I would like to reuse the ImageButton (and other buttons I will add) in another fragment, ideally
without copying its definition
by keeping the definition in xml and not adding it programmatically
I.e. the goal is to overlay the same set of buttons in different fragments.
Is there a way to define all buttons in a separate xml file and load them programmatically on fragment creation?

Yes, You can.
Define all buttons in different xml say layout_buttons.xml
and add them in each fragment layout using
<include layout="#layout/layout_buttons" />

Use XML-design of a listview multiple times

I've written an app and now want to design the UI. The problem is that I have the same data (well, not the same, but the same kind of data since it's an XML readout) and now I wanted to design it. But I don't think I can get the design how I want it programmatically. So I thought I design it once with XML and then copy the layout in the for loop for the other data as well. Is this possible?
If yes, how is it possible? I finished now my XML for one entry and now I want that all the other entries have the same style and layout as the others... Thanks!

There is simple way to achieve this.
There is include tag in xml file which you can use one layout in multiple screen design.
for eg. you had create header for application so no need to use same code in all file, just you can include that portion in each xml file.
here is simple example which may help you.
Create a Re-usable Layout
titlebar.xml
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width=”match_parent”
android:layout_height="wrap_content"
android:background="#color/titlebar_bg">
<ImageView android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="#drawable/gafricalogo" />
</FrameLayout>
Use the Tag:
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width=”match_parent”
android:layout_height=”match_parent”
android:background="#color/app_bg"
android:gravity="center_horizontal">
<include layout="#layout/titlebar"/>
<TextView android:layout_width=”match_parent”
android:layout_height="wrap_content"
android:text="#string/hello"
android:padding="10dp" />
...
</LinearLayout>

You should be using an Adapter to define your ListView elements. In which case, you will define a layout for that adapter (using XML) that will apply to every element in your ListView.
Bottom line, use an Adapter, which will set the same XML layout for every element in your List.
(Check item #3)
http://docs.xamarin.com/guides/android/user_interface/working_with_listviews_and_adapters

Android Centering the content

I'm a total beginner in Android layout, but I want to center the content vertically and horizontally.
So this book I'm reading says this:
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:background="#color/background"
android:layout_height="match_parent"
android:layout_width="match_parent"
android:padding="30dip"
android:orientation="horizontal" >
<LinearLayout
android:orientation="vertical"
android:layout_height="wrap_content"
android:layout_width="fill_parent"
android:layout_gravity="center" >
...component.. etc...
This works and I think i get it, except Eclipse says:
This linearlayout or its parent is useless; transfer the background
attribute to the other view
But I do not understand this?

This linearlayout or its parent is useless; transfer the background
attribute to the other view
means that you can manage the entire layout by the parent it self, you are unnecessarily adding another LinearLayout which can degrade the layout performance
You can use android:gravity="center" instead of android:layout_gravity="center" which a child supplies to its parent.
Solution
you can combine your linear layouts as
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:background="#color/background"
android:orientation="vertical"
android:layout_height="wrap_content"
android:layout_width="fill_parent"
android:gravity="center"
android:padding="30dip"
>

add android:background parameter in both LinearLayout

This linearlayout or its parent is useless; transfer the background
attribute to the other view
This is a warning triggered when any Layout has only one child which is also a Layout. In your case LinearLayout. In these cases one of other can be removed without any problems. It is recommended to remove these redundant layouts. It is.. as it says just a warning, it wont cause any exception, but if you remove that redundant layout that will help improve overall performance

You should share your full code so that everyone get the whole scenario of your problem. Any way you can follow three way to do the things.
Approach One :
android:layout_centerInParent="true"
Above code will make your layout center horizontally and vertically.
Approach two :
And if you want to do individually.(May be needs sometimes)
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
Approach three :
android:gravity="center" (Though I see you have used. May be you have missed any point inside code).
Hope this will help you. Happy coding.

Declaratively defining fragments inside ViewPager

I have 5 unique pages of xml that are fairly complex. I want to put the 5 pages inside a ViewPager. All of the samples I can find simply put identical contents in each page via code. I want to declaratively define the xml in the viewpager like the xml pasted below. But this does not work - the app stops with this xml.
If I can't declaratively define it, then can I load individual xml pages into the viewpager? I can find no examples that do this.
thanks,
Gary Blakely
<?xml version="1.0" encoding="utf-8"?>
<fragment >
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ImageView android:layout_width="match_parent"
android:layout_height="match_parent" android:id="#+id/imageView1"
android:src="#drawable/flashright" android:adjustViewBounds="true" android:scaleType="fitXY">
</ImageView>
</LinearLayout>
</fragment>
<fragment >
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<ImageView android:layout_width="match_parent"
android:layout_height="match_parent" android:id="#+id/imageView1"
android:src="#drawable/flashleft" android:adjustViewBounds="true" android:scaleType="fitXY">
</ImageView>
</LinearLayout>
</fragment>

If I follow, you want to declare everything in XML and avoid any programmatic initialization from within your Activity containing the ViewPager. The only way I can think of doing this would be to define 3 different Fragment classes which reference 3 different xml layouts. You could then embed them in your above xml, replacing each <Fragment> element with <FragmentX> <FragmentY> <FragmentZ> etc. Personally, I would rather write 3 xml layouts and create a single Fragment implementation that takes a single int argument to designate which layout to load, and then do the small amount of programmatic initialization necessary to make such a solution work. The rationale being that there is less duplicated code.
EDIT:
Another approach that might more fully address your requirements is to replace your <Fragment> tags with <Layout> tags and give them id's. Then in your Activity code, store refs to them, remove them from the View in onCreate() and finally add each of the stored references into programmatically created instances of Fragment which you then add to your ViewPager. Very ugly but thats the only way I know of to declaratively define everything in XML. You'll still have the problem that its not clear from the XML that these elements are nested within a ViewPager so personally I don't see the point. ListView and ListFragment operate with the same kind of implicit association though so its not unprecedented.