попробуйте эту функцию
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
buttonSend = (Button) findViewById(R.id.buttonSend);
textTo = (EditText) findViewById(R.id.editTextTo);
textSubject = (EditText) findViewById(R.id.editTextSubject);
textMessage = (EditText) findViewById(R.id.editTextMessage);
buttonSend.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
String to = textTo.getText().toString();
String subject = textSubject.getText().toString();
String message = textMessage.getText().toString();
Intent email = new Intent(Intent.ACTION_SEND);
email.putExtra(Intent.EXTRA_EMAIL, new String[] { to });
// email.putExtra(Intent.EXTRA_CC, new String[]{ to});
// email.putExtra(Intent.EXTRA_BCC, new String[]{to});
email.putExtra(Intent.EXTRA_SUBJECT, subject);
email.putExtra(Intent.EXTRA_TEXT, message);
// need this to prompts email client only
email.setType("message/rfc822");
startActivity(Intent.createChooser(email, "Choose an Email client :"));
}
});
}