From 7e8cc5fe6c09d70f0f37e70a5faa325e205dd5c8 Mon Sep 17 00:00:00 2001
From: huanghongxun <huanghongxun2008@126.com>
Date: Thu, 25 Apr 2019 11:16:59 +0800
Subject: [PATCH] Fix #547

---
 .../hmcl/ui/download/UpdateInstallerWizardProvider.java    | 7 +++++++
 .../org/jackhuang/hmcl/ui/wizard/WizardController.java     | 7 ++++++-
 .../java/org/jackhuang/hmcl/ui/wizard/WizardProvider.java  | 3 +++
 3 files changed, 16 insertions(+), 1 deletion(-)

diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/download/UpdateInstallerWizardProvider.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/download/UpdateInstallerWizardProvider.java
index 655ec03d4..f7285482b 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/download/UpdateInstallerWizardProvider.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/download/UpdateInstallerWizardProvider.java
@@ -85,4 +85,11 @@ public final class UpdateInstallerWizardProvider implements WizardProvider {
     public boolean cancel() {
         return true;
     }
+
+    @Override
+    public boolean cancelIfCannotGoBack() {
+        // VersionsPage will call wizardController.onPrev(cleanUp = true) when list is empty.
+        // So we cancel this wizard when VersionPage calls the method.
+        return true;
+    }
 }
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardController.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardController.java
index b3bb62ed6..816dc511e 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardController.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardController.java
@@ -83,7 +83,12 @@ public class WizardController implements Navigation {
     @Override
     public void onPrev(boolean cleanUp) {
         if (!canPrev()) {
-            throw new IllegalStateException("Cannot go backward since this is the back page. Pages: " + pages);
+            if (provider.cancelIfCannotGoBack()) {
+                onCancel();
+                return;
+            } else {
+                throw new IllegalStateException("Cannot go backward since this is the back page. Pages: " + pages);
+            }
         }
 
         Node page = pages.pop();
diff --git a/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardProvider.java b/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardProvider.java
index fba16613e..bad9e5d9a 100644
--- a/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardProvider.java
+++ b/HMCL/src/main/java/org/jackhuang/hmcl/ui/wizard/WizardProvider.java
@@ -26,6 +26,9 @@ public interface WizardProvider {
     Object finish(Map<String, Object> settings);
     Node createPage(WizardController controller, int step, Map<String, Object> settings);
     boolean cancel();
+    default boolean cancelIfCannotGoBack() {
+        return false;
+    }
 
     interface FailureCallback {
         void onFail(Map<String, Object> settings, Exception exception, Runnable next);