Check for OpenKeychain app

app/src/main/java/eu/faircode/email/FragmentCompose.java

@@ -1975,6 +1975,22 @@ public class FragmentCompose extends FragmentBase {
     private void onMenuEncrypt() {
         EntityIdentity identity = (EntityIdentity) spIdentity.getSelectedItem();
         if (identity == null || identity.encrypt == 0) {
+            final Context context = getContext();
+            if (!Helper.isOpenKeychainInstalled(context)) {
+                new AlertDialog.Builder(context)
+                        .setTitle(R.string.title_no_openpgp)
+                        .setMessage(R.string.title_no_openpgp_remark)
+                        .setPositiveButton(R.string.title_info, new DialogInterface.OnClickListener() {
+                            @Override
+                            public void onClick(DialogInterface dialog, int which) {
+                                Helper.viewFAQ(context, 12);
+                            }
+                        })
+                        .setNegativeButton(android.R.string.cancel, null)
+                        .show();
+                return;
+            }
+
             if (EntityMessage.ENCRYPT_NONE.equals(encrypt) || encrypt == null)
                 encrypt = EntityMessage.PGP_SIGNENCRYPT;
             else if (EntityMessage.PGP_SIGNENCRYPT.equals(encrypt))

app/src/main/res/values/strings.xml

@@ -1650,6 +1650,7 @@
     <string name="title_alternative_text">Load plain text</string>
     <string name="title_alternative_html">Load HTML</string>
     <string name="title_no_openpgp">OpenKeychain not found</string>
+    <string name="title_no_openpgp_remark">PGP end-to-end encryption needs to be configured first</string>
     <string name="title_user_interaction">Transferring to OpenKeychain</string>
     <string name="title_padlock">Use the padlock to decrypt the message</string>
     <string name="title_signed_data">Verify the signature to show the message text</string>