allow to create a special entry in the database with the QuickUnlock code as password, closes https://github.com/PhilippC/keepass2android/issues/331

src/keepass2android/QuickUnlock.cs

@@ -29,6 +29,7 @@ using Android.Preferences;
 using Android.Runtime;
 using Android.Support.Design.Widget;
 using Android.Views.InputMethods;
+using KeePassLib;
 using KeePassLib.Serialization;
 
 namespace keepass2android
@@ -107,7 +108,12 @@ namespace keepass2android
 
 			_quickUnlockLength = App.Kp2a.QuickUnlockKeyLength;
 
-		    if (PreferenceManager.GetDefaultSharedPreferences(this)
+			bool useUnlockKeyFromDatabase = 
+                QuickUnlockFromDatabaseEnabled
+				&& FindQuickUnlockEntry() != null;
+			
+
+            if (useUnlockKeyFromDatabase || PreferenceManager.GetDefaultSharedPreferences(this)
 		        .GetBoolean(GetString(Resource.String.QuickUnlockHideLength_key), false))
 		    {
 		        txtLabel.Text = GetString(Resource.String.QuickUnlock_label_secure);
@@ -157,6 +163,15 @@ namespace keepass2android
 
         }
 
+        private bool QuickUnlockFromDatabaseEnabled =>
+            PreferenceManager.GetDefaultSharedPreferences(this)
+                .GetBoolean(GetString(Resource.String.QuickUnlockKeyFromDatabase_key), false);
+
+        private static PwEntry FindQuickUnlockEntry()
+        {
+            return App.Kp2a.GetDbForQuickUnlock()?.KpDatabase?.RootGroup?.Entries.SingleOrDefault(e => e.Strings.GetSafe(PwDefs.TitleField).ReadString() == "QuickUnlock");
+        }
+
         private const string NumFailedAttemptsKey = "FailedAttempts";
 
         protected override void OnSaveInstanceState(Bundle outState)
@@ -357,7 +372,17 @@ namespace keepass2android
         private string ExpectedPasswordPart
 		{
 			get
-			{
+            {
+                if (QuickUnlockFromDatabaseEnabled)
+                {
+                    var quickUnlockEntry = FindQuickUnlockEntry();
+                    if (quickUnlockEntry != null)
+                    {
+                        return quickUnlockEntry.Strings.ReadSafe(PwDefs.PasswordField).ToString();
+                    }
+				}
+
+                
 				KcpPassword kcpPassword = (KcpPassword) App.Kp2a.GetDbForQuickUnlock().KpDatabase.MasterKey.GetUserKey(typeof (KcpPassword));
 				String password = kcpPassword.Password.ReadString();
 

src/keepass2android/Resources/values/config.xml

@@ -35,6 +35,7 @@
 
   <string name="app_name_debug">KP2ADbg</string>
   <string name="library_name"></string>
+  <string name="QuickUnlockKeyFromDatabase_key">QuickUnlockKeyFromDatabase_key</string>
     <string name="default_file_path">/keepass/keepass.kdbx</string>
     <string name="donate_url"><![CDATA[https://philipp.crocoll.net/donate.php?lang=%1$s&app=%2$s]]></string>
     <string name="homepage">https://github.com/PhilippC/keepass2android</string>

src/keepass2android/Resources/values/strings.xml

@@ -353,7 +353,10 @@
   <string name="QuickUnlockLength_summary">Maximum number of characters used as QuickUnlock password.</string>
   <string name="QuickUnlockHideLength_title">Hide QuickUnlock length</string>
   <string name="QuickUnlockHideLength_summary">If enabled, the length of the QuickUnlock code is not displayed on the QuickUnlock screen.</string>
+  <string name="QuickUnlockKeyFromDatabase_title">QuickUnlock key from database entry</string>
+  <string name="QuickUnlockKeyFromDatabase_summary">If the active database contains an entry with title QuickUnlock in its root group, the password of this entry is used as QuickUnlock code.</string>
   
+
   <string name="QuickUnlock_fail">QuickUnlock failed: incorrect password!</string>
   <string name="SaveAttachmentDialog_title">Save attachment</string>
   <string name="SaveAttachmentDialog_text">Please select where to save the attachment.</string>

src/keepass2android/Resources/xml/preferences.xml

@@ -508,6 +508,14 @@
 		    android:defaultValue="false"
 		    android:title="@string/QuickUnlockHideLength_title"
 		    android:key="@string/QuickUnlockHideLength_key" />
+
+      <CheckBoxPreference
+        android:enabled="true"
+        android:persistent="true"
+        android:summary="@string/QuickUnlockKeyFromDatabase_summary"
+        android:defaultValue="false"
+        android:title="@string/QuickUnlockKeyFromDatabase_title"
+        android:key="@string/QuickUnlockKeyFromDatabase_key" />
       
 		</PreferenceScreen>
 		<PreferenceScreen