Develop Reference

How to display placeholder Chips within ChipGroup in xml?

I have a layout with a ChipGroup whose chips will be populated programmatically, but I want to visualise how chips will look like within the layout, is there a way to show fake chips like for example using the tools namespace?

Not really the solution, you asked for, but it gets the job done.
If someone's got a better solution, let me know.
I solved it with a hardcoded chip, which has the visibility set to GONE and inside the tools namespace visibility set to VISIBLE.
<com.google.android.material.chip.Chip
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:visibility="gone"
tools:visibility="visible"
tools:text="Leichter Genuss" />

Android: Why subtitle in ListView not grey?

I use latest Android Studio and SDK. In preview & real device i see this:
My code:
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="com.myappname.view.AboutActivity">
<ListView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:id="#+id/listViewAbout" />
</RelativeLayout>
How i make subtitle text color is gray? Like this:

I'm going out on a limb and assume that you're using the row layout simple_list_item_2.xml (based on the screenshot) which gives you two rows. The problem, if you may call it that, is that depending on the SDK version, the styling for this layout has changed.
On SDK 23, it looks like this:
However, on say SDK 19, it looks like this:
Why?
To understand this we first need to take a look at the xml that generates the rows from simple_list_item_2.xml, you'll see it's a pretty simple layout that uses the now deprecated view TwoLineListItem but that's just a plus on why to use your custom layout.
<TwoLineListItem xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:minHeight="?attr/listPreferredItemHeight"
android:mode="twoLine"
android:paddingStart="?attr/listPreferredItemPaddingStart"
android:paddingEnd="?attr/listPreferredItemPaddingEnd">
<TextView android:id="#id/text1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginTop="8dp"
android:textAppearance="?attr/textAppearanceListItem" />
<TextView android:id="#id/text2"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_below="#id/text1"
android:layout_alignStart="#id/text1"
android:textAppearance="?attr/textAppearanceListItemSecondary" />
</TwoLineListItem>
The reason is because of the way the style textAppearanceListItemSecondary is resolved in each SDK version. The style is what gives the text the size, the color, etc. The evolution of the interface in Android has given birth to a huge ecosystem of themes and relying on the default styling will result in inconsistencies like the one you stumbled upon.
What to do about it?
You should use your own layout for this to allow for uniform styling across versions. To do so, please refer to any of the multiple questions covering this matter. But in short it just means creating a layout file, call it for example custom_row.xml and having the layout look exactly as you please. This also gives you total control over placement of the items, extra Views that you may need, and overhead in terms of coding is minimal compared to the SimpleAdapter or ArrayAdapter that perhaps you were using.
Note
You should consider moving your code towards RecyclerView instead of ListView if you haven't already.

You can set Textview property
android:textColor="#color/grey"
in you Adapter layout to change colour of your sub item
Hope this will help

What is the ButtonBarLayout and how should we use it?

When I developed, I found a new widget called android.support.v7.widget.ButtonBarLayout unexpectedly. I tried to search it on the internet, but nothing was found, even on the official development documents site.
In the meantime, I found two ButtonBarLayout when I search ButtonBarLayout everywhere in Android Studio, one is android.support.v7.widget.ButtonBarLayout and the other is com.android.internal.widget.ButtonBarLayout. I tried to read source codes of both, I found that they are the same except package name. So I thought maybe android.support.v7.widget.ButtonBarLayout came from com.android.internal.widget.ButtonBarLayout after the internal ButtonBarLayout was through tests and released. At the same time, ButtonBarLayout is inherited from LinearLayout.
But there are some question:
What can we get from ButtonBarLayout literally and how should we use it?
I noticed the variable of private boolean mAllowStacking. When it changes, orientation of this layout would be changed. But I didn't really understand what it is used for.
So does somebody know ButtonBarLayout well?
P.S.: I used Android Studio of 2.0.0 Preview 4 and Gradle Plugin of 2.0.0-alpha3 and Android Support Library of 23.1.1 and Platform-tools of 23.1 and Build-tools of 23.0.2.

As others pointed out, the class description tells exactly what it is: an extension of LinearLayout that automatically switches to vertical orientation when it can't fit its child views horizontally.
I might add that this was clearly done to fit with the material design specifications about dialogs. They make a distinction between side by side buttons and stacked buttons. See for example:
Side-by-side buttons are recommended when the text of each label does
not exceed the maximum button width, such as the commonly used
OK/Cancel buttons.
While you should go for stacked buttons when the single button is too large, or there's not enough room for both:
When text labels exceed the maximum button width, use stacked buttons
to accommodate the text. Affirmative actions are stacked above
dismissive actions.
So, one possible use of this class, is when designing your own dialogs. For example, AlertDialog and AlertDialog.Builder offer internal support for dialogs with buttons, but sometimes you just want to subclass DialogFragment or AppCompatDialogFragment for a better control.
There, it might be useful to setup a bottom button bar that follows the design guidelines, and have full control on the buttons (like enabling and disabling, things you can't do with an AlertDialog AFAIK).

The source code describes ButtonBarLayout as follows:
/**
* An extension of LinearLayout that automatically switches to vertical
* orientation when it can't fit its child views horizontally.
*/
So, in essence, it is nothing but a smart LinearLayout which manages auto-switching orientations based on available space on screen.
The same ButtonBarLayout.java file describes mAllowStacking in comments as follows:
/** Whether the current configuration allows stacking. */
Source Code Here

You are right first of all. ButtonBar layout does not seem to be featured anywhere in the official Android documentation. I tried myself to search about it, but to no avail. However I have found some information which defines what is a ButtonBar layout and when to use it. Hopefully this will help you.
Most tutorials use the Buttonbar layout in a dialogbox or at the bottom of a screen to confirm or decline an option. The image below is a visual representation of how the ButtonBar layout has been used in a screen.
The screenshot above has the following layout xml:
<LinearLayout
style="?android:attr/buttonBarStyle"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<Button
android:id="#+id/Button01"
style="?android:attr/buttonBarButtonStyle"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Show" />
<Button
android:id="#+id/Button02"
style="?android:attr/buttonBarButtonStyle"
android:layout_width="0dp"
android:layout_height="wrap_content"
android:layout_weight="1"
android:text="Change" />
</LinearLayout>
<EditText
android:id="#+id/myView"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:ems="10" >
<requestFocus />
</EditText>
So essentially what Android is doing here is simply creating two buttons next to each other in a LinearLayout with each button having the match_parent parameter set to the width. Hence each button takes half the size of the screen. Android have actually taken away the hassle of creating seperate buttons and positioning them correctly to fit different screens, by creating a simple widget handling this altogether.
As with the support library, Android have implemented this for developers using an earlier API. It is normal for them to use the support library for this purpose.
Hope this helps :)

https://android.googlesource.com/platform/frameworks/base/+/master/core/java/com/android/internal/widget/ButtonBarLayout.java
Looking into the code, I think it's a LinearLayout for buttons (duh). You can probably look at it like the Dialog buttons divided by a vertical spacer: | . AllowStacking will change the orientation to vertical and the gravity to the right instead of bottom. I should try it out to give a better answer

ButtonBarlayout is not featured anywhere in the official Android documentation.
it is used for auto-switching orientations according to the space.

Regarding your question:
How should we use it?
I guess it is undocumented because it is not stable yet.
It just popped up because this long lasting complaint originate from poor ROM modification by device vendor.
https://code.google.com/p/android/issues/detail?id=78377
See #270 for the resolution regarding classpath and why all classes inside .internal. were made public.
And nope even that fix a lot of bugs from poor ROM modification are still out there (in lots of device of well known brands). The issue is soon declined by project member.
I don't think we should use it just yet until the document show up.
Just my $.02 though.

Just to add to the other answers, if you guys want to check the orientation of a ButtonBarLayout you should check the orienation AFTER the value has called on measure.
In other words (Kotlin):
buttonBarLayout.post {
val orientation = buttonBarLayout.orientation
val height = buttonBarLayout.measuredHeight
}

Creating such a Button with Android? (Inspired by iOS)

On an iOS App I saw such a Button:
The same I would like to do in Android, how could I achieve this?
What I tried is the following code:
<Button
android:id="#+id/widget41"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_marginLeft="5dp"
android:layout_marginRight="5dp"
android:text="Email1 testmail#gmail.com"
android:textStyle="bold" />
Looks something like that:
Well just a normal (ugly looking) Button. I have no idea, how I could style it like in iOS. Any suggestions or links would be appreciated!

The best solution would be to create your own custom view that behaves like the iOS counterpart (though, as other users have mentioned, Android does have it's own design guidelines, and the view that you are seeing is an iOS implementation that is designed for that platform).
If you look at the iOS image above (a copy of yours with some parts highlighted), I have split it up into sections.
You could use an Android ViewGroup like a LinearLayout to create the overall image, and give the LinearLayout a border or background (which can be a bitmap image of a rounded rectangle for example (See Android Nine Patch for an example of how to make this fit multiple screens).
Firstly, for the mail icon you would need a LeftAligned ImageView
with appropriate dimensions.
Next up we have a Bold TextView containing the text "Email1".
This is followed by another TextView which is blue and uses the
elipsize property (as defined in an Android XML layout) to create
"..." at the end once the text has reached the max width it can
consume. (Use android:ellipsize="end" in the XML)
Finally we have an indicator image, which again can be an ImageView
sized appropriately.
You could also achieve this with a RelativeLayout, which would allow you to RightAlign the indicator image, LeftAlign the mail icon, and allow the text to fill the space in between that it can get hold of.
Example of Nine Patch use for the background here

That is UITableView in iOS(just like ListView in android). It depends on the list item design you do it. There is no such Button Control in Android.

You should design your own button to looks like iOS one.
Android has it own design guidelines:
http://developer.android.com/design/patterns/pure-android.html

Well, as others have clearly mentioned there is no default Button in Android like this, and for your info neither is in iOS. Its all about the design. Anything is possible, in the end it all comes to how far are you willing to go to achieve it.
Below is a simple code, that will be close to your design.
<TextView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:layout_margin="5dp"
android:background="#drawable/text_background"
android:drawableLeft="#drawable/envelope"
android:drawablePadding="10dp"
android:drawableRight="#drawable/right_arrow"
android:ellipsize="end"
android:gravity="center_vertical"
android:text="#string/email" />
There can be other ways also, like that whole view could be a ViewGroup, either a LinearLayout or a RelativeLayout and there could be multiple TextViews and ImageViews inside that.

Here is a tutorial for creating stylized android buttons. You can round the corners and change the background colors to look like the buttons in ios.
Here is a similar question.
Hope this helps.

Android Layout Elements

I'm trying to make an Android layout like the one below. I have a couple of questions:
1 - what is the element called that FB uses for posts? Ie, it doesn't look like a text view, but the element looks like it separates each post with a divider line. Also, the text style is different for a person's name and how long ago they posted. I'm looking to duplicate this (minus pictures) but I can't find the right UI elements.
What is the element called at the bottom? It's like a static menu. IE, it's the same as a menu but instead of pressing "menu" to access it, it's on the page at all times.
Finally, are there good tutorials/examples on how to make nice looking, professional layouts like the apps on the market? The tutorials that I've found on layouts are really basic. I'd like to understand what elements exist, what all of the attributes mean and see examples, etc. So far I'm only able to see the capabilities from other applications. I'd like to have a handbook or some type of some type of reference manual to go to.

For the "fancy" text views you can make a linear layout that hosts a <RelativeLayout>:
<RelativeLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_height="wrap_content"
android:layout_width="fill_parent"
android:layout_weight="0">
<ImageView
android:id="#+id/userPhoto"
android:layout_height="64dip"
android:layout_width="64dip"
/>
<TextView
android:id="#+id/userFullName"
android:layout_height="25dp"
android:layout_width="fill_parent"
android:layout_marginLeft="70dp"
/>
</RelativeLayout>
Once you have a relative layout you can add different views inside of that to create a sort of customeized view.
As far as good examples I would look at this book. It's easy to understand and very helpful on such things.

I found a really helpful tutorial to solve a problem in ListView Row design a bit like yours. It goes a bit further explaining how to do Async Image loading but the first part should help you.
Also, I might be wrong (I am still a bit new to this) but I think the answer above lacks a TextView for the actual message besides the userName and the relative positions of the elements since it is a relative layout. Something like:
<TextView
android:id="#+id/userName"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignTop="#id/userPhoto"
android:layout_toRightOf="#id/userPhoto"
android:textSize="17dp"
android:textStyle="bold" />
<!-- actual message -->
<TextView
android:id="#+id/message"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:layout_below="#id/userName"
android:layout_marginTop="1dip"
android:layout_toRightOf="#id/userPhoto"
android:textSize="15dp" />
The key in organizing a relative layout is:
android:layout_alignTop="#id/userPhoto"
android:layout_toRightOf="#id/userPhoto"
and
android:layout_below="#id/userName"
android:layout_toRightOf="#id/userPhoto"
I might be wrong but if it helps, great! Just adding my bit to the other answer.
Cheers