AppCompat - Spinner не работи в RelativeLayout

Намерих причината.

Използвам много адаптери и в един от тях случайно прикачих изгледа към основния изглед... Това изглежда не е проблем на повечето устройства и версии на Android, но на някои...

convertView = mInflater.inflate(mLayoutRes, null);

Би трябвало

convertView = mInflater.inflate(mLayoutRes, null, false);

ако адаптерът се използва в Spinner...

Опитайте да използвате следния код:

activity_main.xml

    <RelativeLayout xmlns:androclass="http://schemas.android.com/apk/res/android"  
        xmlns:tools="http://schemas.android.com/tools"  
        android:layout_width="match_parent"  
        android:layout_height="match_parent"  
        tools:context=".MainActivity" >  

        <Spinner  
            android:id="@+id/spinner1"  
            android:layout_width="wrap_content"  
            android:layout_height="wrap_content"  
            android:layout_alignParentTop="true"  
            android:layout_centerHorizontal="true"  
            android:layout_marginTop="83dp" />  

    </RelativeLayout>  

MainActivity.java:

package com.example.spinner;  
import android.app.Activity;  
import android.os.Bundle;  
import android.view.Menu;  
import android.view.View;  
import android.widget.AdapterView;  
import android.widget.ArrayAdapter;  
import android.widget.Spinner;  
import android.widget.TextView;  
import android.widget.Toast;  

public class MainActivity extends Activity implements  
AdapterView.OnItemSelectedListener {  

    String[] country = { "India", "USA", "China", "Japan", "Other",  };  

    @Override  
    protected void onCreate(Bundle savedInstanceState) {  
        super.onCreate(savedInstanceState);  
        setContentView(R.layout.activity_main);  
        //Getting the instance of Spinner and applying OnItemSelectedListener on it  
        Spinner spin = (Spinner) findViewById(R.id.spinner1);  
        spin.setOnItemSelectedListener(this);  


        ArrayAdapter aa = new ArrayAdapter(this,android.R.layout.simple_spinner_item,country);  
        aa.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);  

        spin.setAdapter(aa);  
    }  



    @Override  
    public void onItemSelected(AdapterView<?> arg0, View arg1, int position,long id) {  
        Toast.makeText(getApplicationContext(),country[position] ,Toast.LENGTH_LONG).show();  
    }  

    @Override  
    public void onNothingSelected(AdapterView<?> arg0) {  
        // TODO Auto-generated method stub  

    }  

    @Override  
    public boolean onCreateOptionsMenu(Menu menu) {  
        // Inflate the menu; this adds items to the action bar if it is present.  
        getMenuInflater().inflate(R.menu.activity_main, menu);  
        return true;  
    }  
}  

Хващате изключението, в случай че раздувате оформление, което има само изглед (без ViewGroup). Пример android:layout/simple_spinner_dropdown_item има само CheckedTextView:

<?xml version="1.0" encoding="utf-8"?>
<CheckedTextView xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@android:id/text1"
    style="?android:attr/spinnerDropDownItemStyle"
    android:singleLine="true"
    android:layout_width="match_parent"
    android:layout_height="?android:attr/dropdownListPreferredItemHeight"
    android:ellipsize="marquee"/>

Можете да го поправите, като добавите ViewGroup в оформлението на изгледа на вашия адаптерен елемент:

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical" android:layout_width="match_parent"
    android:layout_height="match_parent">
    <include layout="@android:layout/simple_spinner_dropdown_item"/>
</LinearLayout>

Решението @prom85 не работеше за мен, докато не преминах parent ViewGroup вместо null:

convertView = mInflater.inflate(mLayoutRes, parent, false);