[v2] fix: Files DragAndDrop bugs with OnDomReady and DisableWebViewDrop

This commit fixes the issues reported in #3563:

1. OnDomReady triggering multiple times during drag-and-drop:
   - Root cause: When files are dropped without proper event handling, the
     browser navigates to the dropped file, triggering navigation completion
     callbacks and thus OnDomReady again.
   - Fix: Register drag/drop event handlers early in the runtime JavaScript
     (main.js) before the user has a chance to drop files. These handlers
     call e.preventDefault() for file drops, preventing browser navigation.
   - Added setup() function in draganddrop.js that's called from main.js.
   - Additionally added OnDomReady single-fire guards on all platforms as
     a safety measure.

2. DisableWebViewDrop + EnableFileDrop conflict on Windows:
   - When both options were enabled, AllowExternalDrag(false) was called,
     which blocked ALL drag events including the ones needed for file drops.
   - Now only calls AllowExternalDrag(false) when DisableWebViewDrop is true
     AND EnableFileDrop is false.

Platform-specific changes:
- Windows: Fixed navigationCompleted to only call OnDomReady once
- Linux: Added domReadySent flag to prevent multiple DomReady messages
- macOS: Added domReadySent property to track if DomReady was sent

Fixes #3563

Author: claude

v2/internal/frontend/desktop/darwin/WailsContext.h

@@ -50,6 +50,7 @@
 
 @property bool devtoolsEnabled;
 @property bool defaultContextMenuEnabled;
+@property bool domReadySent;
 
 @property (retain) WKUserContentController* userContentController;
 

v2/internal/frontend/desktop/darwin/WailsContext.m

@@ -473,7 +473,12 @@ - (void)webView:(nonnull WKWebView *)webView stopURLSchemeTask:(nonnull id<WKURL
 }
 
 - (void)webView:(WKWebView *)webView didFinishNavigation:(WKNavigation *)navigation {
-    processMessage("DomReady");
+    // Only send DomReady once to prevent OnDomReady callback from being called
+    // multiple times (e.g., on navigation or page reload)
+    if (!self.domReadySent) {
+        self.domReadySent = YES;
+        processMessage("DomReady");
+    }
 }
 
 - (void)userContentController:(nonnull WKUserContentController *)userContentController didReceiveScriptMessage:(nonnull WKScriptMessage *)message {

v2/internal/frontend/desktop/linux/window.c

@@ -469,11 +469,20 @@ gboolean UnFullscreen(gpointer data)
     return G_SOURCE_REMOVE;
 }
 
+// Flag to track if DomReady has been sent - ensures OnDomReady callback is only called once
+static gboolean domReadySent = FALSE;
+
 static void webviewLoadChanged(WebKitWebView *web_view, WebKitLoadEvent load_event, gpointer data)
 {
     if (load_event == WEBKIT_LOAD_FINISHED)
     {
-        processMessage("DomReady");
+        // Only send DomReady once to prevent OnDomReady callback from being called
+        // multiple times (e.g., on navigation or page reload)
+        if (!domReadySent)
+        {
+            domReadySent = TRUE;
+            processMessage("DomReady");
+        }
     }
 }
 

v2/internal/frontend/desktop/windows/frontend.go

@@ -488,7 +488,13 @@ func (f *Frontend) setupChromium() {
 		chromium.AdditionalBrowserArgs = append(chromium.AdditionalBrowserArgs, arg)
 	}
 
-	if f.frontendOptions.DragAndDrop != nil && f.frontendOptions.DragAndDrop.DisableWebViewDrop {
+	// Only disable external drag if DisableWebViewDrop is true AND EnableFileDrop is false.
+	// When EnableFileDrop is true, we need to allow external drag events so that the
+	// JavaScript handlers can receive file drop events. The JavaScript will prevent
+	// the default browser behavior (navigating to the dropped file).
+	if f.frontendOptions.DragAndDrop != nil &&
+		f.frontendOptions.DragAndDrop.DisableWebViewDrop &&
+		!f.frontendOptions.DragAndDrop.EnableFileDrop {
 		if err := chromium.AllowExternalDrag(false); err != nil {
 			f.logger.Warning("WebView failed to set AllowExternalDrag to false!")
 		}
@@ -901,10 +907,6 @@ func (f *Frontend) ExecJS(js string) {
 }
 
 func (f *Frontend) navigationCompleted(sender *edge.ICoreWebView2, args *edge.ICoreWebView2NavigationCompletedEventArgs) {
-	if f.frontendOptions.OnDomReady != nil {
-		go f.frontendOptions.OnDomReady(f.ctx)
-	}
-
 	if f.frontendOptions.Frameless && f.frontendOptions.DisableResize == false {
 		f.ExecJS("window.wails.flags.enableResize = true;")
 	}
@@ -918,6 +920,12 @@ func (f *Frontend) navigationCompleted(sender *edge.ICoreWebView2, args *edge.IC
 	}
 	f.hasStarted = true
 
+	// Only call OnDomReady on the first navigation completion to prevent
+	// multiple calls when page reloads or navigates (e.g., during file drops)
+	if f.frontendOptions.OnDomReady != nil {
+		go f.frontendOptions.OnDomReady(f.ctx)
+	}
+
 	// Hack to make it visible: https://github.com/MicrosoftEdge/WebView2Feedback/issues/1077#issuecomment-825375026
 	err := f.chromium.Hide()
 	if err != nil {

v2/internal/frontend/runtime/desktop/draganddrop.js

@@ -14,6 +14,7 @@ import {EventsOn, EventsOff} from "./events";
 
 const flags = {
     registered: false,
+    handlersSetup: false,
     defaultUseDropTarget: true,
     useDropTarget: true,
     nextDeactivate: null,
@@ -245,9 +246,9 @@ export function OnFileDrop(callback, useDropTarget) {
 
     const uDTPT = typeof useDropTarget;
     flags.useDropTarget = uDTPT === "undefined" || uDTPT !== "boolean" ? flags.defaultUseDropTarget : useDropTarget;
-    window.addEventListener('dragover', onDragOver);
-    window.addEventListener('dragleave', onDragLeave);
-    window.addEventListener('drop', onDrop);
+
+    // Ensure handlers are set up (idempotent - safe to call multiple times)
+    setup();
 
     let cb = callback;
     if (flags.useDropTarget) {
@@ -274,3 +275,19 @@ export function OnFileDropOff() {
     EventsOff("wails:file-drop");
     flags.registered = false;
 }
+
+/**
+ * setup installs the drag and drop handlers early to prevent browser navigation
+ * when files are dropped. This is called from the runtime initialization to ensure
+ * handlers are in place before the user has a chance to drop files.
+ * The actual file processing only happens when enableWailsDragAndDrop flag is true.
+ */
+export function setup() {
+    if (flags.handlersSetup) {
+        return;
+    }
+    flags.handlersSetup = true;
+    window.addEventListener('dragover', onDragOver);
+    window.addEventListener('dragleave', onDragLeave);
+    window.addEventListener('drop', onDrop);
+}

v2/internal/frontend/runtime/desktop/main.js

@@ -216,4 +216,10 @@ window.addEventListener('contextmenu', function(e) {
     }
 });
 
+// Setup drag and drop handlers early to prevent browser navigation when files are dropped.
+// This must be done before the user has a chance to drop files on the window.
+// The actual file processing only happens when enableWailsDragAndDrop flag is set to true
+// by the backend (via runtime:ready response).
+DragAndDrop.setup();
+
 window.WailsInvoke("runtime:ready");