Sending message through WhatsApp

UPDATE Please refer to https://faq.whatsapp.com/en/android/26000030/?category=5245251

WhatsApp's Click to Chat feature allows you to begin a chat with someone without having their phone number saved in your phone's address book. As long as you know this person’s phone number, you can create a link that will allow you to start a chat with them.

Use: https://wa.me/15551234567

Don't use: https://wa.me/+001-(555)1234567

Example: https://wa.me/15551234567?text=I'm%20interested%20in%20your%20car%20for%20sale

Original answer Here is the solution

public void onClickWhatsApp(View view) {
    
    PackageManager pm=getPackageManager();
    try {

        Intent waIntent = new Intent(Intent.ACTION_SEND);
        waIntent.setType("text/plain");
        String text = "YOUR TEXT HERE";

        PackageInfo info=pm.getPackageInfo("com.whatsapp", PackageManager.GET_META_DATA);
        //Check if package exists or not. If not then code 
        //in catch block will be called
        waIntent.setPackage("com.whatsapp");

        waIntent.putExtra(Intent.EXTRA_TEXT, text);
        startActivity(Intent.createChooser(waIntent, "Share with"));
        
   } catch (NameNotFoundException e) {
        Toast.makeText(this, "WhatsApp not Installed", Toast.LENGTH_SHORT)
                .show();
   }  

}

Also see http://www.whatsapp.com/faq/en/android/28000012

With this code you can open the whatsapp chat with the given number.

void openWhatsappContact(String number) {
    Uri uri = Uri.parse("smsto:" + number);
    Intent i = new Intent(Intent.ACTION_SENDTO, uri);
    i.setPackage("com.whatsapp");  
    startActivity(Intent.createChooser(i, ""));
}