Develop Reference

When changing ActionBarSize, leaves an small margin to layout below

I am using the code below for changing actionbar size.
<style name="AppTheme" parent="Theme.MaterialComponents.Light.DarkActionBar">
<item name="colorPrimary">#color/colorPrimary</item>
<item name="colorPrimaryDark">#color/colorPrimaryDark</item>
<item name="colorAccent">#color/colorAccent</item>
<item name="android:textAllCaps">false</item>
<item name="android:windowFullscreen">true</item>
<item name="actionBarSize">26.0dip</item>
</style>
Here is my result
Image
Why this margin exists on child?

Button Style does not work in Android Studio

T'm using the newest Android Studio Version to code my app and I can't change the button style.
It seems like when generating a new project, it already has some default styles for buttons which I can't seem to be able to override.
Everytime I place just a plane button it already has some background color ("colorPrimary") and if I'm trying to apply a style, it only changes the text of the button, but not the shape or the color.
This is my style:
<style name="buttonStartStyle">
<item name="android:background">#drawable/button_style1</item>
<item name="android:layout_margin">20dp</item>
<item name="android:textColor">#color/white</item>
<item name="android:textAllCaps">false</item>
<item name="android:textSize">18sp</item>
<item name="android:layout_width">match_parent</item>
<item name="android:layout_height">wrap_content</item>
</style>
and my button_style1.xml:
<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item>
<shape android:shape="rectangle">
<corners android:radius="50dp"/>
<solid android:color="#color/smoothWhite"/>
<size android:height="50dp"/>
<gradient android:startColor="#color/green_card" android:endColor="#color/green_main"/>
</shape>
</item>
The button already looks like this when I place it right from the pallete:
My xml code for the button:
<Button
android:id="#+id/button"
style="#style/buttonStartStyle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button"
tools:layout_editor_absoluteX="121dp"
tools:layout_editor_absoluteY="244dp" />
This is how the button looks with the style applied:
Here is my themes.xml:
<resources xmlns:tools="http://schemas.android.com/tools">
<!-- Base application theme. -->
<style name="Theme.B_app" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
<!-- Primary brand color. -->
<item name="colorPrimary">#color/green_dark</item>
<item name="colorPrimaryVariant">#color/black</item>
<item name="colorOnPrimary">#color/white</item>
<!-- Secondary brand color. -->
<item name="colorSecondary">#color/teal_200</item>
<item name="colorSecondaryVariant">#color/teal_700</item>
<item name="colorOnSecondary">#color/black</item>
<!-- Status bar color. -->
<item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
<!-- Customize your theme here. -->
</style>
<style name="Theme.B_app.NoActionBar">
<item name="windowActionBar">false</item>
<item name="windowNoTitle">true</item>
</style>
<style name="Theme.B_app.AppBarOverlay" parent="ThemeOverlay.AppCompat.Dark.ActionBar" />
<style name="Theme.B_app.PopupOverlay" parent="ThemeOverlay.AppCompat.Light" />
<style name="buttonStartStyle">
<item name="android:background">#drawable/button_style1</item>
<item name="android:layout_margin">20dp</item>
<item name="android:textColor">#color/white</item>
<item name="android:textAllCaps">false</item>
<item name="android:textSize">18sp</item>
<item name="android:layout_width">match_parent</item>
<item name="android:layout_height">wrap_content</item>
</style>
<style name="testStyle">
<item name="android:background">#drawable/button_style2</item>
<item name="android:layout_margin">20dp</item>
<item name="android:textColor">#color/white</item>
<item name="android:textAllCaps">false</item>
<item name="android:textSize">18sp</item>
<item name="android:layout_width">match_parent</item>
<item name="android:layout_height">wrap_content</item>
</style>
<style name="FlatButton" parent="Theme.AppCompat.Light">
<item name="android:textColor">#color/grey_dark</item>
<item name="colorControlHighlight">#color/white</item>
</style>

I see two possibilites:
You might not have the right parent for your Button. Try:
<style name="buttonStartStyle" parent ="android:Widget.Button">
attributes might be changed along the way in your program. Try setting the needed attributes to null before applying the style.

The problem here is likely with the parent style in themes.xml.
If the parent theme is one of the Material Components ones for example:
<style name="Theme.StyleDemo2" parent="Theme.MaterialComponents.DayNight.DarkActionBar">
<!-- Primary brand color. -->
<item name="colorPrimary">#color/purple_500</item>
<item name="colorPrimaryVariant">#color/purple_700</item>
<item name="colorOnPrimary">#color/white</item>
<!-- Secondary brand color. -->
<item name="colorSecondary">#color/teal_200</item>
<item name="colorSecondaryVariant">#color/teal_700</item>
<item name="colorOnSecondary">#color/black</item>
<!-- Status bar color. -->
<item name="android:statusBarColor" tools:targetApi="l">?attr/colorPrimaryVariant</item>
<!-- Customize your theme here. -->
</style>
This overrides any style changes you might make to give your button the material theme with a tint color defined by the colorPrimary item in the theme (they are also not standard buttons in this instance but some funky sub class replaced quietly). To overcome this issue change the parent theme to something such as:
parent="Theme.AppCompat.Light"
This one is much more customizable and your button styles will take effect.

DatePickerDialog buttons not showing the label

The two buttons at the bottom will not show the labels. This is how I am instantiating the date picker new DatePickerDialog(classname.this, date, myCalendar
.get(Calendar.YEAR), myCalendar.get(Calendar.MONTH),
myCalendar.get(Calendar.DAY_OF_MONTH)).show();
I am running Android Studio 3.2 Canary and target sdk of 28.

You can use this to apply material button style :
<style name="AppTheme" parent="Theme.MaterialComponents.Light.NoActionBar">
<!-- Customize your theme here. -->
<item name="colorPrimary">#color/colorPrimary</item>
<item name="colorPrimaryDark">#color/colorPrimaryDark</item>
<item name="colorAccent">#color/colorAccent</item>
<item name="android:buttonBarPositiveButtonStyle">#style/Widget.MaterialComponents.Button</item>
<item name="android:buttonBarNegativeButtonStyle">#style/Widget.MaterialComponents.Button.TextButton</item>
<item name="android:buttonBarNeutralButtonStyle">#style/Widget.MaterialComponents.Button</item>
</style>
Result : materialDatePicker

Check for <item name="colorAccent">#color/colorAccent</item> in your styles.xml, button text color will be same as value of colorAccent in colors.xml.
Edit:-
Update your style as following, It will work:
<!-- Base application theme. -->
<style name="AppTheme" parent="Theme.MaterialComponents.Light.DarkActionBar">
<!-- Customize your theme here. -->
<item name="colorPrimary">#color/colorPrimary</item>
<item name="colorPrimaryDark">#color/colorPrimaryDark</item>
<item name="colorAccent">#color/colorAccent</item>
<item name="android:buttonBarPositiveButtonStyle">#style/DialogButtonStyled</item>
<item name="android:buttonBarNegativeButtonStyle">#style/DialogButtonStyled</item>
<item name="android:buttonBarNeutralButtonStyle">#style/DialogButtonStyled</item>
</style>
<style name="DialogButtonStyled" parent="Theme.MaterialComponents.Light">
<item name="android:textColor">#color/colorWhite</item>
</style>

Cannot Change Action Bar Text Color

I have read several threads on this topic and have implemented the below code. However, I cannot change change the text color of my Action Bar text:
<style name="AppTheme.NoActionBar">
<item name="android:statusBarColor">#android:color/white</item>
<item name="windowActionBar">false</item>
<item name="windowNoTitle">true</item>
<item name="android:textColor">#color/white</item>
<item name="android:actionBarStyle">#style/MyTheme.ActionBarStyle</item>
</style>
<style name="MyTheme.ActionBarStyle" parent="#style/Widget.AppCompat.Light.ActionBar">
<item name="android:titleTextStyle">#style/MyTheme.ActionBar.TitleTextStyle</item>
</style>
<style name="MyTheme.ActionBar.TitleTextStyle" parent="#style/TextAppearance.AppCompat.Widget.ActionBar.Title">
<item name="android:textColor">#color/white</item>
</style>

<style name="AppThemeLight" parent="Theme.AppCompat.Light.DarkActionBar">
...
<item name="android:textColorPrimary">#color/yourColor</item>
</style>
I use Toolbar and this works for me. Too bad i couldn't repeat it with inheritance.

How to change color green in oficial timerpicker?

This is my code of theme, how change color in dialog timerpicker?
<style name="AppBaseTheme" parent="Theme.AppCompat.Light.DarkActionBar">
</style>
<!-- Application theme. -->
<style name="AppTheme" parent="AppBaseTheme">
<item name="colorPrimary">#color/primary</item>
<item name="colorPrimaryDark">#color/primary_dark</item>
<item name="colorAccent">#color/accent</item>
</style>