How to set the drop-down arrow in the spinner- How to set dropdown arrow in spinner?

problem ：

I tried to set spinner with drop down arrow but i couldn't fix it can anyone help me with this? I tried to set the spinner with the drop-down arrow , But I can't fix it. Can anyone help me ？I have attached the source code. I attached the source code .

my class file: My class file ：

    import android.os.Bundle;    import android.view.View;    import android.widget.AdapterView;    import android.widget.ArrayAdapter;    import android.widget.Button;    import android.widget.EditText;    import android.widget.Spinner;    import android.widget.AdapterView.OnItemSelectedListener;    import android.widget.Toast;        public class topup extends Activity  {            Spinner spinner,spin1,spin2,spin3;                EditText ed,ed1;                Button btn;                List<String> list, list1,list2,list3;                    private String[] countries_list={"01","02","03","04","05","06","07","08","09","10","11","12"};                    protected void onCreate(Bundle savedInstanceState) {                        super.onCreate(savedInstanceState);                        setContentView(R.layout.topup);                        spinner = (Spinner) findViewById(R.id.spinner1);                        spin1= (Spinner) findViewById(R.id.spinner2);                        spin2= (Spinner) findViewById(R.id.spinner3);                        spin3= (Spinner) findViewById(R.id.spinner4);                        ed = (EditText) findViewById(R.id.editText3);                        list = new ArrayList<String>();                        list.add("");                        list.add("select");                        list.add("01");                        list.add("02");                        list.add("03");                        list.add("04");                        list.add("05");                        list.add("06");                        list.add("07");                        list.add("08");                        list.add("09");                        list.add("10");                        list.add("11");                        list.add("12");                        ArrayAdapter<String> adp = new ArrayAdapter<String>                            (this, android.R.layout.simple_spinner_item, list);                        //adp.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);                        spinner.setAdapter(adp);                        spinner.setOnItemSelectedListener(new OnItemSelectedListener() {                            //@Override                            public void onItemSelected(AdapterView<?> parent, View arg1,int arg2, long arg3) {                                // TODO Auto-generated method stub                                 String item = spinner.getItemAtPosition(1).toString();                                 //Toast.makeText(spinner.getContext(), "Selected: " + item, Toast.LENGTH_LONG).show();                                 String ss=spinner.getSelectedItem().toString();                                 String                             }                            public void onNothingSelected(AdapterView<?> arg0) {                                // TODO Auto-generated method stub                            }                        });

my xml file: my xml file ：

<?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"    android:background="@drawable/back1"    android:paddingBottom="@dimen/activity_vertical_margin"    android:paddingLeft="@dimen/activity_horizontal_margin"    android:paddingRight="@dimen/activity_horizontal_margin"    android:paddingTop="@dimen/activity_vertical_margin"    tools:context=".MainActivity" >    <LinearLayout        android:id="@+id/linearLayout1"        android:layout_width="wrap_content"        android:layout_height="55dp"        android:layout_alignParentLeft="true"        android:layout_alignParentRight="true"        android:layout_alignParentTop="true"        android:layout_marginTop="20dp"         android:background="@drawable/red">        <Spinner            android:id="@+id/spinner1"            android:layout_width="match_parent"            android:layout_height="match_parent"            android:dropDownWidth="fill_parent"          />    </LinearLayout>    <EditText        android:id="@+id/editText1"        android:layout_width="wrap_content"        android:layout_height="55dp"        android:layout_alignLeft="@+id/linearLayout1"        android:layout_alignRight="@+id/linearLayout1"        android:layout_below="@+id/linearLayout1"        android:layout_marginTop="25dp"        android:background="@drawable/red"        android:ems="10"        android:hint="enter card number" >        <requestFocus />    </EditText>    <LinearLayout        android:id="@+id/linearLayout2"        android:layout_width="wrap_content"        android:layout_height="55dp"        android:layout_alignLeft="@+id/editText1"        android:layout_alignRight="@+id/editText1"        android:layout_below="@+id/editText1"        android:layout_marginTop="33dp"        android:orientation="horizontal"         android:background="@drawable/red">        <Spinner            android:id="@+id/spinner3"            android:layout_width="72dp"            android:layout_height="wrap_content"             />        <Spinner            android:id="@+id/spinner2"            android:layout_width="72dp"            android:layout_height="wrap_content"             />        <EditText            android:id="@+id/editText2"            android:layout_width="22dp"            android:layout_height="match_parent"            android:layout_weight="0.18"            android:ems="10"            android:hint="enter cvv" />    </LinearLayout>    <LinearLayout        android:id="@+id/linearLayout3"        android:layout_width="wrap_content"        android:layout_height="55dp"        android:layout_alignParentLeft="true"        android:layout_alignRight="@+id/linearLayout2"        android:layout_below="@+id/linearLayout2"        android:layout_marginTop="26dp"        android:orientation="vertical"        android:background="@drawable/red" >    </LinearLayout>    <Spinner        android:id="@+id/spinner4"        android:layout_width="15dp"        android:layout_height="18dp"        android:layout_alignBottom="@+id/linearLayout3"        android:layout_alignLeft="@+id/linearLayout3"        android:layout_alignRight="@+id/linearLayout3"        android:layout_alignTop="@+id/linearLayout3"      />    <Button        android:id="@+id/button1"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_alignParentLeft="true"        android:layout_alignParentRight="true"        android:layout_below="@+id/linearLayout3"        android:layout_marginTop="18dp"        android:text="Add Amount"         android:background="@drawable/buttonsty"/></RelativeLayout>

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Solution ：

Reference resources ： https://stackoom.com/en/question/1Ngu2