Disallow push message if no applications exist

Fixes #179

app/src/main/java/com/github/gotify/messages/provider/ApplicationHolder.java

@@ -13,6 +13,7 @@ import java.util.List;
 public class ApplicationHolder {
     private List<Application> state;
     private Runnable onUpdate;
+    private Runnable onUpdateFailed;
     private Activity activity;
     private ApiClient client;
 
@@ -35,11 +36,12 @@ public class ApplicationHolder {
 
     private void onReceiveApps(List<Application> apps) {
         state = apps;
-        onUpdate.run();
+        if (onUpdate != null) onUpdate.run();
     }
 
     private void onFailedApps(ApiException e) {
         Utils.showSnackBar(activity, "Could not request applications, see logs.");
+        if (onUpdateFailed != null) onUpdateFailed.run();
     }
 
     public List<Application> get() {
@@ -49,4 +51,8 @@ public class ApplicationHolder {
     public void onUpdate(Runnable runnable) {
         this.onUpdate = runnable;
     }
+
+    public void onUpdateFailed(Runnable runnable) {
+        this.onUpdateFailed = runnable;
+    }
 }

app/src/main/java/com/github/gotify/sharing/ShareActivity.java

@@ -6,7 +6,9 @@ import android.os.Bundle;
 import android.view.MenuItem;
 import android.view.View;
 import android.widget.ArrayAdapter;
+import android.widget.Button;
 import android.widget.EditText;
+import android.widget.LinearLayout;
 import android.widget.Spinner;
 import android.widget.Toast;
 import androidx.appcompat.app.ActionBar;
@@ -46,6 +48,12 @@ public class ShareActivity extends AppCompatActivity {
     @BindView(R.id.appSpinner)
     Spinner appSpinner;
 
+    @BindView(R.id.push_button)
+    Button pushMessageButton;
+
+    @BindView(R.id.missingAppsContainer)
+    LinearLayout missingAppsInfo;
+
     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
@@ -73,7 +81,16 @@ public class ShareActivity extends AppCompatActivity {
         ApiClient client =
                 ClientFactory.clientToken(settings.url(), settings.sslSettings(), settings.token());
         appsHolder = new ApplicationHolder(this, client);
-        appsHolder.onUpdate(() -> populateSpinner(appsHolder.get()));
+        appsHolder.onUpdate(
+                () -> {
+                    List<Application> apps = appsHolder.get();
+                    populateSpinner(apps);
+
+                    boolean appsAvailable = !apps.isEmpty();
+                    pushMessageButton.setEnabled(appsAvailable);
+                    missingAppsInfo.setVisibility(appsAvailable ? View.GONE : View.VISIBLE);
+                });
+        appsHolder.onUpdateFailed(() -> pushMessageButton.setEnabled(false));
         appsHolder.request();
     }
 
@@ -98,6 +115,11 @@ public class ShareActivity extends AppCompatActivity {
         } else if (priority.isEmpty()) {
             Toast.makeText(this, "Priority should be number.", Toast.LENGTH_LONG).show();
             return;
+        } else if (appIndex == Spinner.INVALID_POSITION) {
+            // For safety, e.g. loading the apps needs too much time (maybe a timeout) and
+            // the user tries to push without an app selected.
+            Toast.makeText(this, "An app must be selected.", Toast.LENGTH_LONG).show();
+            return;
         }
 
         Message message = new Message();

app/src/main/res/drawable/ic_info.xml

@@ -0,0 +1,9 @@
+<vector xmlns:android="http://schemas.android.com/apk/res/android"
+    android:width="24dp"
+    android:height="24dp"
+    android:viewportWidth="24"
+    android:viewportHeight="24">
+  <path
+      android:fillColor="@color/icons"
+      android:pathData="M12,2C6.48,2 2,6.48 2,12s4.48,10 10,10 10,-4.48 10,-10S17.52,2 12,2zM13,17h-2v-6h2v6zM13,9h-2L11,7h2v2z"/>
+</vector>

app/src/main/res/layout/activity_share.xml

@@ -1,7 +1,13 @@
 <?xml version="1.0" encoding="utf-8"?>
-<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
+<ScrollView
+    xmlns:android="http://schemas.android.com/apk/res/android"
+    xmlns:app="http://schemas.android.com/apk/res-auto"
     android:layout_width="match_parent"
-    android:layout_height="match_parent"
+    android:layout_height="match_parent">
+
+    <LinearLayout
+        android:layout_width="match_parent"
+        android:layout_height="wrap_content"
         android:orientation="vertical">
 
         <include
@@ -81,12 +87,48 @@
                 android:textSize="18sp" />
         </LinearLayout>
 
+        <LinearLayout
+            android:id="@+id/missingAppsContainer"
+            android:layout_width="match_parent"
+            android:layout_height="wrap_content"
+            android:layout_marginHorizontal="20dp"
+            android:layout_marginBottom="20dp"
+            android:gravity="center"
+            android:orientation="horizontal"
+            android:paddingStart="10dp"
+            android:paddingEnd="10dp"
+            android:visibility="gone">
+
+            <ImageView
+                android:id="@+id/missingAppsIcon"
+                android:layout_width="40dp"
+                android:layout_height="match_parent"
+                android:layout_weight="0"
+                app:srcCompat="@drawable/ic_info" />
+
+            <Space
+                android:layout_width="10dp"
+                android:layout_height="match_parent"
+                android:layout_weight="0" />
+
+            <TextView
+                android:id="@+id/missingAppsText"
+                android:layout_width="wrap_content"
+                android:layout_height="match_parent"
+                android:layout_weight="0"
+                android:text="@string/push_missing_app_info"
+                android:textAlignment="center"
+                android:visibility="visible" />
+        </LinearLayout>
+
         <Button
             android:id="@+id/push_button"
             android:layout_width="match_parent"
             android:layout_height="wrap_content"
             android:layout_gravity="center_vertical|center_horizontal"
-        android:layout_marginBottom="20dp"
             android:layout_marginHorizontal="20dp"
+            android:layout_marginBottom="20dp"
             android:text="@string/push_button" />
+
     </LinearLayout>
+</ScrollView>

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

@@ -81,5 +81,6 @@
     <string name="push_title_hint">Title</string>
     <string name="push_content_hint">Content</string>
     <string name="push_priority_hint">Priority</string>
+    <string name="push_missing_app_info">There are no applications available on the server to push a message to.</string>
     <string name="message_copied_to_clipboard">Content copied to clipboard</string>
 </resources>