sending whatsapp message to spesific contact using android

Question

I'm looking for sending whatsapp message to spesific contact and i try this code but it doesn't work with me the code open the spesific contact but it doesn't send the message

String message="at first";
try {
    Uri uri = Uri.parse("smsto:"+"+999999999");
    Intent sendIntent = new Intent(Intent.ACTION_SENDTO, uri);
    //sendIntent.setAction(Intent.ACTION_SEND);
    //sendIntent.putExtra(Intent.EXTRA_TEXT, "This is my text to send.");
    //sendIntent.setType("text/plain");
    sendIntent.setPackage("com.whatsapp");
    if sendIntent!= null) {
        sendIntent.putExtra(Intent.EXTRA_TEXT, "This is my text to send.");
        startActivity(sendIntent);
    }else{
        Toast.makeText(this, "WhatsApp not Installed", Toast.LENGTH_SHORT).show();
    }
    message="done";
}catch(Exception ex){
    message="Error: "+ex.toString();
}finally{
    TextView mas = (TextView) findViewById(R.id.mas);
    mas.setText(message);
}