AccountManager accountManager = AccountManager.get(this); // this 는 context 를 포함해야 한다.
Account[] accounts = accountManager.getAccounts();

AccountManager accountManager = AccountManager.get(this);
Account[] accounts = accountManager.getAccountsByType("com.google");

Intent intent = KeyChain.createInstallIntent();
byte[] p12Bytes = //... read from file, such as example.pfx or example.p12...
intent.putExtra(KeyChain.EXTRA_PKCS12, p12Bytes);
startActivity(intent)

KeyChain.choosePrivateKeyAlias(this, this, new String[]{"RSA"}, null, null, -1, null);

public class KeychainTest extends Activity implements ..., KeyChainAliasCallback
{
    //...

    @Override
    public void alias(final String alias)
    {
        Log.e("MyApp", "Alias is " + alias);

        try
        {
            PrivateKey privateKey = KeyChain.getPrivateKey(this, alias);
            X509Certificate[] certificateChain = KeyChain.getCertificateChain(this, alias);
        }
        catch ...
    }

    //...
}

/Generate a key and store it in the KeyStore
final KeyGenerator keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
final KeyGenParameterSpec keyGenParameterSpec = new KeyGenParameterSpec.Builder("MyKeyAlias",
        KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
        .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
        .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
        //.setUserAuthenticationRequired(true) //requires lock screen, invalidated if lock screen is disabled
        //.setUserAuthenticationValidityDurationSeconds(120) //only available x seconds from password authentication. -1 requires finger print - every time
        .setRandomizedEncryptionRequired(true) //different ciphertext for same plaintext on each call
        .build();
keyGenerator.init(keyGenParameterSpec);
keyGenerator.generateKey();

private HashMap<String, byte[]> encrypt(final byte[] decryptedBytes)
{
    final HashMap<String, byte[]> map = new HashMap<String, byte[]>();
    try
    {
        //Get the key
        final KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
        keyStore.load(null);
        final KeyStore.SecretKeyEntry secretKeyEntry = (KeyStore.SecretKeyEntry)keyStore.getEntry("MyKeyAlias", null);
        final SecretKey secretKey = secretKeyEntry.getSecretKey();

        //Encrypt data
        final Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        cipher.init(Cipher.ENCRYPT_MODE, secretKey);
        final byte[] ivBytes = cipher.getIV();
        final byte[] encryptedBytes = cipher.doFinal(decryptedBytes);
        map.put("iv", ivBytes);
        map.put("encrypted", encryptedBytes);
    }
    catch (Throwable e)
    {
        e.printStackTrace();
    }

    return map;
}

private byte[] decrypt(final HashMap<String, byte[]> map)
{
    byte[] decryptedBytes = null;
    try
    {
        //Get the key
        final KeyStore keyStore = KeyStore.getInstance("AndroidKeyStore");
        keyStore.load(null);
        final KeyStore.SecretKeyEntry secretKeyEntry = (KeyStore.SecretKeyEntry)keyStore.getEntry("MyKeyAlias", null);
        final SecretKey secretKey = secretKeyEntry.getSecretKey();

        //Extract info from map
        final byte[] encryptedBytes = map.get("encrypted");
        final byte[] ivBytes = map.get("iv");

        //Decrypt data
        final Cipher cipher = Cipher.getInstance("AES/GCM/NoPadding");
        final GCMParameterSpec spec = new GCMParameterSpec(128, ivBytes);
        cipher.init(Cipher.DECRYPT_MODE, secretKey, spec);
        decryptedBytes = cipher.doFinal(encryptedBytes);
    }
    catch (Throwable e)
    {
        e.printStackTrace();
    }

    return decryptedBytes;
}

@TargetApi(Build.VERSION_CODES.M)
private void testEncryption()
{
    try
    {
        //Generate a key and store it in the KeyStore
        final KeyGenerator keyGenerator = KeyGenerator.getInstance(KeyProperties.KEY_ALGORITHM_AES, "AndroidKeyStore");
        final KeyGenParameterSpec keyGenParameterSpec = new KeyGenParameterSpec.Builder("MyKeyAlias",
                KeyProperties.PURPOSE_ENCRYPT | KeyProperties.PURPOSE_DECRYPT)
                .setBlockModes(KeyProperties.BLOCK_MODE_GCM)
                .setEncryptionPaddings(KeyProperties.ENCRYPTION_PADDING_NONE)
                //.setUserAuthenticationRequired(true) //requires lock screen, invalidated if lock screen is disabled
                //.setUserAuthenticationValidityDurationSeconds(120) //only available x seconds from password authentication. -1 requires finger print - every time
                .setRandomizedEncryptionRequired(true) //different ciphertext for same plaintext on each call
                .build();
        keyGenerator.init(keyGenParameterSpec);
        keyGenerator.generateKey();

        //Test
        final HashMap<String, byte[]> map = encrypt("My very sensitive string!".getBytes("UTF-8"));
        final byte[] decryptedBytes = decrypt(map);
        final String decryptedString = new String(decryptedBytes, "UTF-8");
        Log.e("MyApp", "The decrypted string is " + decryptedString);
    }
    catch (Throwable e)
    {
        e.printStackTrace();
    }
}