HybridWebView: Invoke JS methods from .NET

src/Controls/samples/Controls.Sample/Pages/Controls/HybridWebViewPage.xaml

@@ -8,22 +8,39 @@
 
     <Grid ColumnDefinitions="2*,1*" RowDefinitions="Auto,1*">
 
-        <Label
+      <Editor
           Grid.Row="0"
           Grid.Column="0"
           Text="HybridWebView here"
-          x:Name="statusLabel" />
+          IsReadOnly="True"
+          MinimumHeightRequest="200"
+          x:Name="statusText" />
 
-        <Button
+      <VerticalStackLayout
           Grid.Row="0"
-          Grid.Column="1"
+          Grid.Column="1">
+
+        <Button
+          Margin="10"
           Text="Send message to JS"
           Clicked="SendMessageButton_Clicked" />
 
-        <HybridWebView
+        <Button
+          Margin="10"
+          Text="Invoke JS"
+          Clicked="InvokeJSMethodButton_Clicked" />
+
+        <Button
+          Margin="10"
+          Text="Invoke Async JS"
+          Clicked="InvokeAsyncJSMethodButton_Clicked" />
+
+      </VerticalStackLayout>
+
+      <HybridWebView
           x:Name="hwv"
           Grid.Row="1"
-          Grid.ColumnSpan="2"
+          Grid.ColumnSpan="3"
           HybridRoot="HybridSamplePage"
           RawMessageReceived="hwv_RawMessageReceived"/>
 

src/Controls/samples/Controls.Sample/Pages/Controls/HybridWebViewPage.xaml.cs

@@ -1,4 +1,7 @@
 using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text.Json.Serialization;
 using Microsoft.Maui.Controls;
 
 namespace Maui.Controls.Sample.Pages
@@ -10,14 +13,76 @@ public HybridWebViewPage()
 			InitializeComponent();
 		}
 
+		int count;
 		private void SendMessageButton_Clicked(object sender, EventArgs e)
 		{
-			hwv.SendRawMessage("Hello from C#!");
+			hwv.SendRawMessage($"Hello from C#! #{count++}");
+		}
+
+		private async void InvokeJSMethodButton_Clicked(object sender, EventArgs e)
+		{
+			var statusResult = "";
+
+			var x = 123d;
+			var y = 321d;
+			var result = await hwv.InvokeJavaScriptAsync<ComputationResult>(
+				"AddNumbers",
+				SampleInvokeJsContext.Default.ComputationResult,
+				new object?[] { x, null, y, null },
+				new[] { SampleInvokeJsContext.Default.Double, null, SampleInvokeJsContext.Default.Double, null });
+
+			if (result is null)
+			{
+				statusResult += Environment.NewLine + $"Got no result for operation with {x} and {y} 😮";
+			}
+			else
+			{
+				statusResult += Environment.NewLine + $"Used operation {result.operationName} with numbers {x} and {y} to get {result.result}";
+			}
+
+			Dispatcher.Dispatch(() => statusText.Text += statusResult);
+		}
+
+		private async void InvokeAsyncJSMethodButton_Clicked(object sender, EventArgs e)
+		{
+			var statusResult = "";
+
+			var asyncFuncResult = await hwv.InvokeJavaScriptAsync<Dictionary<string,string>>(
+				"EvaluateMeWithParamsAndAsyncReturn",
+				SampleInvokeJsContext.Default.DictionaryStringString,
+				new object?[] { "new_key", "new_value" },
+				new[] { SampleInvokeJsContext.Default.String, SampleInvokeJsContext.Default.String });
+
+			if (asyncFuncResult == null)
+			{
+				statusResult += Environment.NewLine + $"Got no result from EvaluateMeWithParamsAndAsyncReturn 😮";
+			}
+			else
+			{
+				statusResult += Environment.NewLine + $"Got result from EvaluateMeWithParamsAndAsyncReturn: {string.Join(",", asyncFuncResult)}";
+			}
+
+			Dispatcher.Dispatch(() => statusText.Text += statusResult);
 		}
 
 		private void hwv_RawMessageReceived(object sender, HybridWebViewRawMessageReceivedEventArgs e)
 		{
-			Dispatcher.Dispatch(() => statusLabel.Text += e.Message);
+			Dispatcher.Dispatch(() => statusText.Text += Environment.NewLine + e.Message);
+		}
+
+		public class ComputationResult
+		{
+			public double result { get; set; }
+			public string? operationName { get; set; }
+		}
+
+		[JsonSourceGenerationOptions(WriteIndented = true)]
+		[JsonSerializable(typeof(ComputationResult))]
+		[JsonSerializable(typeof(double))]
+		[JsonSerializable(typeof(string))]
+		[JsonSerializable(typeof(Dictionary<string, string>))]
+		internal partial class SampleInvokeJsContext : JsonSerializerContext
+		{
 		}
 	}
 }

src/Controls/samples/Controls.Sample/Resources/Raw/HybridSamplePage/asyncdata.txt

@@ -0,0 +1,4 @@
+{
+    "key1": "value1",
+    "key2": "value2"
+}

src/Controls/samples/Controls.Sample/Resources/Raw/HybridSamplePage/index.html

@@ -4,6 +4,7 @@
 <head>
     <meta charset="utf-8" />
     <title></title>
+    <link rel="icon" href="data:,">
     <link rel="stylesheet" href="styles/app.css">
     <script src="scripts/HybridWebView.js"></script>
     <script>
@@ -13,14 +14,39 @@
                 var messageFromCSharp = document.getElementById("messageFromCSharp");
                 messageFromCSharp.value += '\r\n' + e.detail.message;
             });
+
+        function AddNumbers(a, x, b, y) {
+            var result = {
+                "result": a + b,
+                "operationName": "Addition"
+            };
+            return result;
+        }
+
+        var count = 0;
+
+        async function EvaluateMeWithParamsAndAsyncReturn(s1, s2) {
+            const response = await fetch("/asyncdata.txt");
+            if (!response.ok) {
+                    throw new Error(`HTTP error: ${response.status}`);
+            }
+            var jsonData = await response.json();
+
+            jsonData[s1] = s2;
+
+            const msg = 'JSON data is available: ' + JSON.stringify(jsonData);
+            window.HybridWebView.SendRawMessage(msg)
+
+            return jsonData;
+        }
     </script>
 </head>
 <body>
     <div>
         Hybrid sample!
     </div>
     <div>
-        <button onclick="window.HybridWebView.SendRawMessage('Message from JS!')">Send message to C#</button>
+        <button onclick="window.HybridWebView.SendRawMessage('Message from JS! ' + (count++))">Send message to C#</button>
     </div>
     <div>
         Message from C#: <textarea readonly id="messageFromCSharp" style="width: 80%; height: 10em;"></textarea>

src/Controls/samples/Controls.Sample/Resources/Raw/HybridSamplePage/scripts/HybridWebView.js

@@ -1,48 +1,78 @@
-function HybridWebViewInit() {
-
-    function DispatchHybridWebViewMessage(message) {
-        const event = new CustomEvent("HybridWebViewMessageReceived", { detail: { message: message } });
-        window.dispatchEvent(event);
-    }
+window.HybridWebView = {
+    "Init": function () {
+        function DispatchHybridWebViewMessage(message) {
+            const event = new CustomEvent("HybridWebViewMessageReceived", { detail: { message: message } });
+            window.dispatchEvent(event);
+        }
 
-    if (window.chrome && window.chrome.webview) {
-        // Windows WebView2
-        window.chrome.webview.addEventListener('message', arg => {
-            DispatchHybridWebViewMessage(arg.data);
-        });
-    }
-    else if (window.webkit && window.webkit.messageHandlers && window.webkit.messageHandlers.webwindowinterop) {
-        // iOS and MacCatalyst WKWebView
-        window.external = {
-            "receiveMessage": message => {
-                DispatchHybridWebViewMessage(message);
-            }
-        };
-    }
-    else {
-        // Android WebView
-        window.addEventListener('message', arg => {
-            DispatchHybridWebViewMessage(arg.data);
-        });
-    }
-}
+        if (window.chrome && window.chrome.webview) {
+            // Windows WebView2
+            window.chrome.webview.addEventListener('message', arg => {
+                DispatchHybridWebViewMessage(arg.data);
+            });
+        }
+        else if (window.webkit && window.webkit.messageHandlers && window.webkit.messageHandlers.webwindowinterop) {
+            // iOS and MacCatalyst WKWebView
+            window.external = {
+                "receiveMessage": message => {
+                    DispatchHybridWebViewMessage(message);
+                }
+            };
+        }
+        else {
+            // Android WebView
+            window.addEventListener('message', arg => {
+                DispatchHybridWebViewMessage(arg.data);
+            });
+        }
+    },
 
-window.HybridWebView = {
     "SendRawMessage": function (message) {
+        window.HybridWebView.__SendMessageInternal('RawMessage', message);
+    },
+
+    "__SendMessageInternal": function (type, message) {
+
+        const messageToSend = type + '|' + message;
 
         if (window.chrome && window.chrome.webview) {
             // Windows WebView2
-            window.chrome.webview.postMessage(message);
+            window.chrome.webview.postMessage(messageToSend);
         }
         else if (window.webkit && window.webkit.messageHandlers && window.webkit.messageHandlers.webwindowinterop) {
             // iOS and MacCatalyst WKWebView
-            window.webkit.messageHandlers.webwindowinterop.postMessage(message);
+            window.webkit.messageHandlers.webwindowinterop.postMessage(messageToSend);
         }
         else {
             // Android WebView
-            hybridWebViewHost.sendRawMessage(message);
+            hybridWebViewHost.sendMessage(messageToSend);
         }
+    },
+
+    "InvokeMethod": function (taskId, methodName, args) {
+        if (methodName[Symbol.toStringTag] === 'AsyncFunction') {
+            // For async methods, we need to call the method and then trigger the callback when it's done
+            const asyncPromise = methodName(...args);
+            asyncPromise
+                .then(asyncResult => {
+                    window.HybridWebView.__TriggerAsyncCallback(taskId, asyncResult);
+                })
+                .catch(error => console.error(error));
+        } else {
+            // For sync methods, we can call the method and trigger the callback immediately
+            const syncResult = methodName(...args);
+            window.HybridWebView.__TriggerAsyncCallback(taskId, syncResult);
+        }
+    },
+
+    "__TriggerAsyncCallback": function (taskId, result) {
+        // Make sure the result is a string
+        if (result && typeof (result) !== 'string') {
+            result = JSON.stringify(result);
+        }
+
+        window.HybridWebView.__SendMessageInternal('InvokeMethodCompleted', taskId + '|' + result);
     }
 }
 
-HybridWebViewInit();
+window.HybridWebView.Init();