Develop Reference

FAB - square on pre Lollipop and without shadow on Lollipop

It looks like FloatingActionButton is not working ether on Android 4.0 and Lollipop. As you can see on image below, on Android Lollipopo shadow is missing and on Android 4.1.1 it's square :/
Anyone faced this issue?
Library version:
compile 'com.android.support:design:22.2.0'
Code:
<android.support.design.widget.FloatingActionButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:src="#drawable/abc_ic_clear_mtrl_alpha"/>

Thanks to #harism comment, simply setting app:borderWidth="0dp" resolve both issues.
Note: don't forget to add xmlns:app="http://schemas.android.com/apk/res-auto" to your root layout.

If the FAB still appears as square after setting borderWidth to 0dp, make sure that you aren't setting android:background in your XML or calling setBackgroundColor in code.
You should use android:backgroundTint (XML) or setSupportBackgroundTintList (code)

#Raghunandan, I have same problem on Lollipop also.
Finally I find that the root cause is a drawable named "fab_background" in my drawable folder.
The drawable is previously used for my own fab implementation.
Now I can see round fab after I rename this drawable.

Setting
app:borderWidth="0dp"
works. But if you are getting rendering issues in Android studio and have the Renderer set to Android M or 22, set it to 21

Seems to be a bug. A developer said "Fixed internally. Will be out soon.".

Unknown attribute android:elevation

I'm trying to follow a tutorial that suppose to show how to add a floating button and in the tutorial it says to add the attribute android:elevation to the buttons xml like this:
<ImageButton
android:layout_width="30dp"
android:layout_height="30dp"
android:id="#+id/editButton"
android:layout_gravity="center|right"
android:clickable="false"
android:background="#drawable/edit_grey"
android:layout_marginRight="1dp"
android:elevation="#dimen/elevation_low"/>
but it dosen't recognize that attribute...i believe it has something to do with my project target or sdk...can somebody help me?

To use android:elevation, just as with any other Android 5.0 API, you must compile against Android 5.0 (API 21). This does not mean you have to change your target SDK level or minimum SDK level.
Note: your XML file may still give a warning that android:elevation only works on Android 5.0 or higher. This warning just serves to tell you that previous versions of Android will not have an elevation shadow on the floating action button. However, that does not cause an error - previous versions of Android will ignore XML attributes they do not understand.

The Elevation attribute is pretty new. It defines the lift of the view it is applied to. It is used for the Material Design in the newest Android Versions.
Material Design
You can use it on API Level 21, I guess your targeted Level is lower than this.
If you just want to achieve some shadowing you can use this:
Shadow Drawables for Views
Or you can use the SupportLibrary with CardViews or something like that, they support elevation from API Level 7:
[How-to] Use the v21 Support Libs on Older Versions & Target L While Remaining Backwards-Compatible
Hope this helps.

Can't set alpha of ImageView in XML

I'm compiling using API 16, but with the minimum supported API set to 8. I'm trying to set the alpha of an ImageView in XML, but every time I use
<ImageView
android:id="#+id/image"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:alpha="0"
.
.
. />
AAPT complains that alpha isn't a valid attribute, even if the documentation in the android site states that ImageView's supposed to inherit it from View.
Is this a bug, or is this really how it's supposed to work. I'd set the Visibility, but that won't work well with my animations to show and hide the image.

Yes. You said that your min is 8. However, the View's alpha xml attribute doesn't appear until API Level 11.
http://developer.android.com/reference/android/view/View.html#setAlpha(float)

Setting Alpha level on view doesn't work

I am trying to set the alpha level of a view.
I am reading the documentation here:
http://developer.android.com/reference/android/widget/RelativeLayout.html
and it seems as if it should be possible even on android 2.1 which I am developing for (as I cant see it saying otherwise) but when I add it to my view
<View
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:layout_margin="20sp"
android:background="#ffffff"
android:alpha="0.9"></View>
I get an error saying:
No resource identifier found for attribute 'alpha' in package
'android'
How do I set the alpha level of a view?

you can set the alpha with the background properties like this way
android:background="#50ffffff"
here the first 50 value is set the alpha value

On which android version are you running this?
setAlpha is only available on api level 11. You might try some other way to do this if you want to do this in previous versions. Probably using a semi-transparent background could do it.

dividers between TabWidgets

Is the android:divider attribute under the TabWidget working? I tried the Tab Layout tutorial from android just to test (http://developer.android.com/resources/tutorials/views/hello-tabwidget.html) and set the android:divider to some image (for now I used the android vertical scrollbar as the drawable to really emphasize if its getting picked up (copied it from frameworks), but when I ran it on the emulator, it doesn't appear to be working. According to the docs, the TabWidget does seem to support this attribute: "Drawable used to draw the divider between tabs."
Can anyone help? I am using a nine-patched drawable as my divider image drawable.
MB

It doesn't look like the divider attribute is available anymore for TabWidget. One way to add a custom divider is to set it programmatically:
mTabHost.getTabWidget().setDividerDrawable(R.drawable.divider_vertical_dark);
Make sure however, you call this before you set the content of the tabs. It would crash on me if I called it after.

I had the problem in ICS, where divider was visible. None of the solutions worked except for the following.
<TabWidget
android:id="#android:id/tabs"
android:layout_width="match_parent"
android:layout_height="60dp"
android:gravity="bottom"
android:layout_alignParentBottom="true"
android:fadingEdge="none"
android:showDividers="none" >
</TabWidget>
Key line was android:showDividers="none"

I had this issue and solved it with the following code
tabHost1.getTabWidget().setDividerDrawable(R.drawable.example1);
if(Build.VERSION.SDK_INT >= 11)
tabHost1.getTabWidget().setShowDividers(TabWidget.SHOW_DIVIDER_MIDDLE);
For api levels below 11, it worked with the first line. For 11 and higher I included this to get this working. setShowDividers is added in linearlayout from api level 11. Hope this helps someone

Having the same issue myself. I only see the problem in Ice Cream Sandwich (ICS / 4.0.x). In android 1.6 - 2.3.4 there is no issue, dividers show up properly when setting a drawable in code, or in the xml layout.
I've tried just about everything I can think of to fix it but nothing works, including Josh's answer above :( though I have noticed that when setting any drawable as the divider, it will take up the space between tabs as if there was a drawable there, but it's just not visible.
Hopefully that gives someone else a hint as to what could be happening..?

I removed divider line from tabbar with use of below magical lines.
mTabHost.getTabWidget().setDividerDrawable(null);
OR
mTabHost.getTabWidget().setDividerDrawable(R.Color.transperant);