spinner = (Spinner)getView().findViewById(R.id.spinner);

 String[] datos = getResources().getStringArray(R.array.items);

 ArrayAdapter<String> adaptador = new ArrayAdapter<String>(getActivity(),
            android.R.layout.simple_spinner_item, datos);
adaptador.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

 spinner.setAdapter(adaptador);

<Spinner
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/spinner"
        android:layout_margin="26dp"
        android:textColor="#FFF"/>

<string-array name="items">
    <item >Item 1</item>
    <item >Item 2</item>
    <item >Item 3</item>
    <item >Item 4</item>
</string-array>

<Spinner
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/spinner"
    android:layout_margin="26dp"
    android:textColor="#000000"/>  //change this

android:entries="@array/items" //add this in your spinner layout

<TextView
    xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:textSize="20sp"
    android:gravity="left"
    android:background="#000000"  //dark background
    android:text="Test"
    android:textColor="#ffffff"  //white text
    android:padding="5dp"
    />

ArrayAdapter<String> adaptador = new ArrayAdapter<String>(getActivity(),
        R.layout.spinner_item, datos);

<Spinner
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:id="@+id/spinner"
    android:layout_margin="26dp"
    android:textColor="@android:color/black"
    android:entries="@array/items"/>

String[] datos = getResources().getStringArray(R.array.items);

 ArrayAdapter<String> adaptador = new ArrayAdapter<String>(getActivity(),
            android.R.layout.simple_spinner_item, datos);adaptador.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);

 spinner.setAdapter(adaptador);

<resources>
<string-array name="planets_array">
    <item>Mercury</item>
    <item>Venus</item>
    <item>Earth</item>
    <item>Mars</item>
    <item>Jupiter</item>
    <item>Saturn</item>
    <item>Uranus</item>
    <item>Neptune</item>
</string-array>

Spinner spinner = (Spinner) findViewById(R.id.spinner);
  // Create an ArrayAdapter using the string array and a default spinner layout
ArrayAdapter<CharSequence> adapter = ArrayAdapter.createFromResource(this,
R.array.planets_array, android.R.layout.simple_spinner_item);
 // Specify the layout to use when the list of choices appears
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
// Apply the adapter to the spinner

 spinner.setAdapter(adapter);

public class SpinnerActivity extends Activity implements OnItemSelectedListener {
...

public void onItemSelected(AdapterView<?> parent, View view,
        int pos, long id) {
    // An item was selected. You can retrieve the selected item using
    // parent.getItemAtPosition(pos)
}

public void onNothingSelected(AdapterView<?> parent) {
    // Another interface callback
}
 }

spinner.setOnItemSelectedListener(this);

<Spinner android:id="@+id/spinnerMuestreo"
      android:layout_toEndOf="@+id/textViewNumMuestreo"
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:padding="8dp" <!--Try adding this line. -->
/>