How to create custom spinner like border around the spinner with down triangle on the right side?

I want to develop custom spinner like line around spinner with triangle at right bottom corner.
like following image

For above fig I wrote my custom spinner like a

spinner.xml

 <Spinner android:background="@drawable/spinner_background"/>

spinner_background.xml

<?xml version="1.0" encoding="UTF-8"?>

http://schemas.android.com/apk/res/android">

<item android:state_pressed="true"
      android:drawable="@drawable/spinner_ab_pressed_new_theme_bs">
    <shape>
        
        <solid 
            android:color="@color/White" />
        
 		<corners android:radius="3dp" />
 		
        <padding 
            android:bottom="10dp" 
            android:left="10dp" 
            android:right="10dp" 
            android:top="10dp" />
        
         <stroke 
            android:width="2dp" 
            android:color="@color/skyblue" />
    </shape>
 </item>
 <!-- spinner_ab_default_new_theme_bs -> this image for corner triangle -->
<item
    
    android:drawable="@drawable/spinner_ab_default_new_theme_bs" >
    <shape>
        <solid
            android:color="@color/White">
        </solid>
        
        <corners android:radius="3dp" />
        
        <padding
            android:bottom="10dp" 
            android:left="10dp" 
            android:right="10dp" 
            android:top="10dp" />
         <stroke 
            android:width="2dp" 
            android:color="@color/gray"/>
    </shape>
</item>

And I got output like following image

I tried lot but not achieve my goal please anybody have solution to develop spinner.
like above first one image.

Spinner

<Spinner
    android:id="@+id/To_Units"
    style="@style/spinner_style" />

style.xml

    <style name="spinner_style">
          <item name="android:layout_width">match_parent</item>
          <item name="android:layout_height">wrap_content</item>
          <item name="android:background">@drawable/gradient_spinner</item>
          <item name="android:layout_margin">10dp</item>
          <item name="android:paddingLeft">8dp</item>
          <item name="android:paddingRight">20dp</item>
          <item name="android:paddingTop">5dp</item>
          <item name="android:paddingBottom">5dp</item>
          <item name="android:popupBackground">#DFFFFFFF</item>
     </style>

gradient_spinner.xml (in drawable folder)

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">

    <item><layer-list>
            <item><shape>
                    <gradient android:angle="90" android:endColor="#B3BBCC" android:startColor="#E8EBEF" android:type="linear" />

                    <stroke android:width="1dp" android:color="#000000" />

                    <corners android:radius="4dp" />

                    <padding android:bottom="3dp" android:left="3dp" android:right="3dp" android:top="3dp" />
                </shape></item>
            <item ><bitmap android:gravity="bottom|right" android:src="@drawable/spinner_arrow" />
            </item>
        </layer-list></item>

</selector>  

@drawable/spinner_arrow is your bottom right corner image

This is a simple one.

your_layout.xml

<android.support.v7.widget.AppCompatSpinner
  android:layout_width="match_parent"
  android:layout_height="wrap_content"
  android:background="@drawable/spinner_background"
/>

In the drawable folder, spinner_background.xml

<?xml version="1.0" encoding="utf-8"?>
<selector xmlns:android="http://schemas.android.com/apk/res/android">
  <item><layer-list>
    <item>
        <shape>
            <solid
                android:color="@color/colorWhite">
            </solid>

            <corners android:radius="3dp" />

            <padding
                android:bottom="10dp"
                android:left="10dp"
                android:right="10dp"
                android:top="10dp" />
            <stroke
                android:width="2dp"
                android:color="@color/colorDarkGrey"/>
        </shape>
    </item>
    <item >
        <bitmap android:gravity="bottom|right"
        android:src="@drawable/ic_arrow_drop_down_black_24dp" />
    </item>
  </layer-list></item>
</selector>

Preview:

You can achieve the following by using a single line in your spinner declaration in XML:

Just add this: style="@android:style/Widget.Holo.Light.Spinner"

This is a default generated style in android. It doesn't contain borders around it though. For that you'd better search something on google.

Hope this helps.

UPDATE: AFter a lot of digging I got something which works well for introducing border around spinner.

<?xml version="1.0" encoding="utf-8"?>
<layer-list xmlns:android="http://schemas.android.com/apk/res/android">
    <item
        android:bottom="8dp"
        android:top="8dp">
        <shape>
            <solid android:color="@android:color/white" />
            <corners android:radius="4dp" />
            <stroke
                android:width="2dp"
                android:color="#9E9E9E" />
            <padding
                android:bottom="16dp"
                android:left="8dp"
                android:right="16dp"
                android:top="16dp" />
        </shape>
    </item>
</layer-list>

Place this in the drawable folder and use it as a background for spinner. Like this:

<RelativeLayout
        android:id="@+id/speaker_relative_layout"
        android:layout_width="0dp"
        android:layout_height="70dp"
        android:layout_marginEnd="8dp"
        android:layout_marginLeft="8dp"
        android:layout_marginRight="8dp"
        android:layout_marginStart="8dp"
        android:layout_marginTop="16dp"
        android:background="@drawable/spinner_style"
        app:layout_constraintLeft_toLeftOf="parent"
        app:layout_constraintRight_toRightOf="parent"
        app:layout_constraintTop_toTopOf="parent">

        <Spinner
            android:id="@+id/select_speaker_spinner"
            style="@style/Widget.AppCompat.DropDownItem.Spinner"
            android:layout_width="match_parent"
            android:layout_height="70dp"
            android:entries="@array/select_speaker_spinner_array"
            android:spinnerMode="dialog" />

    </RelativeLayout>

There are two ways to achieve this.

1- As already proposed u can set the background of your spinner as custom 9 patch Image with all the adjustments made into it .

android:background="@drawable/btn_dropdown" 
android:clickable="true"
android:dropDownVerticalOffset="-10dip"
android:dropDownHorizontalOffset="0dip"
android:gravity="center"

If you want your Spinner to show With various different background colors i would recommend making the drop down image transparent, & loading that spinner in a relative layout with your color set in.

btn _dropdown is as:

<selector xmlns:android="http://schemas.android.com/apk/res/android">
<item
    android:state_window_focused="false" android:state_enabled="true"
    android:drawable="@drawable/spinner_default" />
<item
    android:state_window_focused="false" android:state_enabled="false"
    android:drawable="@drawable/spinner_default" />
<item
    android:state_pressed="true"
    android:drawable="@drawable/spinner_pressed" />
<item
    android:state_focused="true" android:state_enabled="true"
    android:drawable="@drawable/spinner_pressed" />
<item
    android:state_enabled="true"
    android:drawable="@drawable/spinner_default" />
<item
    android:state_focused="true"
    android:drawable="@drawable/spinner_pressed" />
<item
    android:drawable="@drawable/spinner_default" />
</selector>

where the various states of pngwould define your various States of spinner seleti

To change only "background" (add corners, change color, ....) you can put it into FrameLayout with wanted background drawable, else you need to make nine patch background for to not lose spinner arrow. Spinner background is transparent.

If you don't prefer to create multiple XML files, try:

<com.google.android.material.card.MaterialCardView
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        app:strokeWidth="1dp"
        app:strokeColor="@color/black"
        app:cardCornerRadius="4dp">

        <androidx.appcompat.widget.AppCompatSpinner
            android:id="@+id/spinner"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:padding="20dp"/>

    </com.google.android.material.card.MaterialCardView>

To change the border color:

app:strokeColor="YOUR_COLOR_HERE"

To change the border's width:

app:strokeWidth="YOUR_DP_WIDTH_HERE"

You could design a simple nine-patch png image and use it as the background of spinner. Using GIMP you can put both border and right triangle in image.

It's super easy you can just add this to your Adapter -> getDropDownView

getDropDownView:

convertView.setBackground(getContext().getResources().getDrawable(R.drawable.bg_spinner_dropdown));

bg_spinner_dropdown:

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    <solid android:color="@color/white" />
    <corners
        android:bottomLeftRadius=enter code here"25dp"
        android:bottomRightRadius="25dp"
        android:topLeftRadius="25dp"
        android:topRightRadius="25dp" />
</shape>