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HybridWebView Bi-Directional Exception Handling (#31521)
* Initial plan * Implement HybridWebView C# exception bubbling to JavaScript - Extended DotNetInvokeResult to include error information fields - Modified InvokeDotNetAsync to return structured error responses instead of null - Updated TypeScript/JavaScript to detect and throw errors from C# responses - Added comprehensive tests for exception handling scenarios - Created test HTML page for exception testing Co-authored-by: mattleibow <1096616+mattleibow@users.noreply.github.com> * Add demo exception handling to HybridWebView sample - Added ThrowException and ThrowExceptionAsync methods to demonstrate new functionality - Added JavaScript functions to test and showcase exception catching - Added UI buttons to trigger exception handling tests - Updated sample to show both error and success scenarios Co-authored-by: mattleibow <1096616+mattleibow@users.noreply.github.com> * Add JavaScript exception handling tests for HybridWebView Co-authored-by: mattleibow <1096616+mattleibow@users.noreply.github.com> * Handle reflection exceptions * AI was right! --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: mattleibow <1096616+mattleibow@users.noreply.github.com> Co-authored-by: Matthew Leibowitz <mattleibow@live.com>
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‎src/Controls/samples/Controls.Sample/Pages/Controls/HybridWebViewPage.xaml‎

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@@ -35,6 +35,16 @@
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Text="Invoke Async JS"
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Clicked="InvokeAsyncJSMethodButton_Clicked" />
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<Button
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Margin="10"
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Text="Test JS Exception"
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Clicked="InvokeJSExceptionButton_Clicked" />
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<Button
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Margin="10"
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Text="Test JS Async Exception"
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Clicked="InvokeJSAsyncExceptionButton_Clicked" />
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</VerticalStackLayout>
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<HybridWebView

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

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@@ -74,6 +74,52 @@ private void hwv_RawMessageReceived(object sender, HybridWebViewRawMessageReceiv
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Dispatcher.Dispatch(() => statusText.Text += Environment.NewLine + e.Message);
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}
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private async void InvokeJSExceptionButton_Clicked(object sender, EventArgs e)
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{
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var statusResult = "";
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try
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{
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statusResult += Environment.NewLine + "Calling JavaScript function that throws exception...";
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var result = await hwv.InvokeJavaScriptAsync<string>(
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"ThrowJavaScriptError",
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SampleInvokeJsContext.Default.String,
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[],
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[]);
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statusResult += Environment.NewLine + "JavaScript function unexpectedly succeeded with result: " + result;
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}
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catch (Exception ex)
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{
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statusResult += Environment.NewLine + $"Caught JavaScript exception in C#: {ex.GetType().Name} - {ex.Message}";
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}
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Dispatcher.Dispatch(() => statusText.Text += statusResult);
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}
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private async void InvokeJSAsyncExceptionButton_Clicked(object sender, EventArgs e)
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{
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var statusResult = "";
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try
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{
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statusResult += Environment.NewLine + "Calling async JavaScript function that throws exception...";
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var result = await hwv.InvokeJavaScriptAsync<string>(
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"ThrowJavaScriptErrorAsync",
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SampleInvokeJsContext.Default.String,
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[],
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[]);
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statusResult += Environment.NewLine + "Async JavaScript function unexpectedly succeeded with result: " + result;
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}
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catch (Exception ex)
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{
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statusResult += Environment.NewLine + $"Caught async JavaScript exception in C#: {ex.GetType().Name} - {ex.Message}";
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}
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Dispatcher.Dispatch(() => statusText.Text += statusResult);
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}
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public class ComputationResult
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{
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public double result { get; set; }
@@ -153,6 +199,21 @@ public async Task<SyncReturn> DoAsyncWorkParamsReturn(int i, string s)
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Value = i,
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};
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}
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// Demo method that throws an exception to showcase error handling
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public void ThrowException()
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{
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Debug.WriteLine("ThrowException called - about to throw");
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throw new InvalidOperationException("This is a test exception thrown from C# code!");
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}
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// Demo async method that throws an exception
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public async Task<string> ThrowExceptionAsync()
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{
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Debug.WriteLine("ThrowExceptionAsync called - about to throw");
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await Task.Delay(100);
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throw new ArgumentException("This is an async test exception thrown from C# code!");
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}
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}
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public class SyncReturn

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

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@@ -93,6 +93,44 @@
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LogMessage("Invoked DoAsyncWorkParamsReturn, return value: message=" + retValue.Message + ", value=" + retValue.Value);
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}
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// Demo functions to test exception handling
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async function InvokeThrowException() {
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LogMessage("Invoking ThrowException");
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try {
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await window.HybridWebView.InvokeDotNet('ThrowException');
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LogMessage("ThrowException unexpectedly succeeded!");
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} catch (ex) {
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LogMessage("Caught exception from ThrowException: " + ex.message);
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LogMessage("Exception type: " + (ex.dotNetErrorType || "Unknown"));
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if (ex.dotNetStackTrace) {
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LogMessage("Stack trace: " + ex.dotNetStackTrace.substring(0, 200) + "...");
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}
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}
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}
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async function InvokeThrowExceptionAsync() {
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LogMessage("Invoking ThrowExceptionAsync");
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try {
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const result = await window.HybridWebView.InvokeDotNet('ThrowExceptionAsync');
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LogMessage("ThrowExceptionAsync unexpectedly succeeded with result: " + result);
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} catch (ex) {
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LogMessage("Caught async exception from ThrowExceptionAsync: " + ex.message);
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LogMessage("Exception type: " + (ex.dotNetErrorType || "Unknown"));
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}
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}
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// JavaScript functions that throw exceptions (for testing C# exception handling of JS calls)
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function ThrowJavaScriptError() {
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LogMessage("ThrowJavaScriptError called - about to throw");
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throw new Error("This is a test error thrown from JavaScript code!");
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}
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async function ThrowJavaScriptErrorAsync() {
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LogMessage("ThrowJavaScriptErrorAsync called - about to throw");
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await new Promise(resolve => setTimeout(resolve, 100));
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throw new Error("This is an async test error thrown from JavaScript code!");
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}
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</script>
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</head>
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<body>
@@ -114,6 +152,16 @@
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<button onclick="InvokeDoAsyncWorkReturn()">Call C# async method (no params) and get simple return value</button>
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<button onclick="InvokeDoAsyncWorkParamsReturn()">Call C# async method (params) and get complex return value</button>
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</div>
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<div>
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<strong>Exception Handling Tests:</strong>
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<button onclick="InvokeThrowException()">Test C# Exception Handling</button>
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<button onclick="InvokeThrowExceptionAsync()">Test C# Async Exception Handling</button>
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</div>
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<div>
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<strong>JavaScript Exception Tests (called from C#):</strong>
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<button onclick="ThrowJavaScriptError()">Test JS Exception</button>
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<button onclick="ThrowJavaScriptErrorAsync()">Test JS Async Exception</button>
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</div>
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<div>
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Log: <textarea readonly id="messageLog" style="width: 80%; height: 10em;"></textarea>
119167
</div>

‎src/Controls/tests/DeviceTests/Elements/HybridWebView/HybridWebViewTests_ExceptionHandling.cs‎

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#nullable enable
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using System;
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using System.Threading.Tasks;
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using Xunit;
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namespace Microsoft.Maui.DeviceTests;
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[Category(TestCategory.HybridWebView)]
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#if WINDOWS
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[Collection(WebViewsCollection)]
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#endif
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public partial class HybridWebViewTests_ExceptionHandling : HybridWebViewTestsBase
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{
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[Fact]
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public Task CSharpMethodThatThrowsException_ShouldPropagateToJavaScript() =>
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RunTest("exception-tests.html", async (hybridWebView) =>
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{
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var invokeJavaScriptTarget = new TestExceptionMethods();
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hybridWebView.SetInvokeJavaScriptTarget(invokeJavaScriptTarget);
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// Tell JavaScript to invoke the method that throws an exception
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hybridWebView.SendRawMessage("ThrowException");
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// Wait for JavaScript to handle the exception
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await WebViewHelpers.WaitForHtmlStatusSet(hybridWebView);
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// Check that JavaScript caught the exception
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var caughtError = await hybridWebView.EvaluateJavaScriptAsync("GetLastError()");
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Assert.Equal("Test exception message", caughtError);
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// Check that the method was called before throwing
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Assert.Equal("ThrowException", invokeJavaScriptTarget.LastMethodCalled);
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});
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[Fact]
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public Task CSharpAsyncMethodThatThrowsException_ShouldPropagateToJavaScript() =>
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RunTest("exception-tests.html", async (hybridWebView) =>
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{
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var invokeJavaScriptTarget = new TestExceptionMethods();
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hybridWebView.SetInvokeJavaScriptTarget(invokeJavaScriptTarget);
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// Tell JavaScript to invoke the async method that throws an exception
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hybridWebView.SendRawMessage("ThrowExceptionAsync");
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// Wait for JavaScript to handle the exception
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await WebViewHelpers.WaitForHtmlStatusSet(hybridWebView);
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// Check that JavaScript caught the async exception
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var caughtError = await hybridWebView.EvaluateJavaScriptAsync("GetLastError()");
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Assert.Equal("Async test exception", caughtError);
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// Check that the method was called before throwing
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Assert.Equal("ThrowExceptionAsync", invokeJavaScriptTarget.LastMethodCalled);
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});
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[Fact]
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public Task CSharpMethodThatThrowsCustomException_ShouldIncludeExceptionDetails() =>
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RunTest("exception-tests.html", async (hybridWebView) =>
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{
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var invokeJavaScriptTarget = new TestExceptionMethods();
61+
hybridWebView.SetInvokeJavaScriptTarget(invokeJavaScriptTarget);
62+
63+
// Tell JavaScript to invoke the method that throws a custom exception
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hybridWebView.SendRawMessage("ThrowCustomException");
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// Wait for JavaScript to handle the exception
67+
await WebViewHelpers.WaitForHtmlStatusSet(hybridWebView);
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69+
// Check that JavaScript caught the exception with custom details
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var errorType = await hybridWebView.EvaluateJavaScriptAsync("GetLastErrorType()");
71+
var errorMessage = await hybridWebView.EvaluateJavaScriptAsync("GetLastErrorMessage()");
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Assert.Equal("ArgumentException", errorType);
74+
Assert.Equal("Custom argument exception", errorMessage);
75+
});
76+
77+
[Fact]
78+
public Task CSharpMethodThatSucceeds_ShouldStillWorkNormally() =>
79+
RunTest("exception-tests.html", async (hybridWebView) =>
80+
{
81+
var invokeJavaScriptTarget = new TestExceptionMethods();
82+
hybridWebView.SetInvokeJavaScriptTarget(invokeJavaScriptTarget);
83+
84+
// Tell JavaScript to invoke a normal method that doesn't throw
85+
hybridWebView.SendRawMessage("SuccessMethod");
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87+
// Wait for JavaScript to complete
88+
await WebViewHelpers.WaitForHtmlStatusSet(hybridWebView);
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// Check that JavaScript got the normal result
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var result = await hybridWebView.EvaluateJavaScriptAsync("GetLastResult()");
92+
Assert.Contains("Success!", result, StringComparison.Ordinal);
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94+
// Check that no error was thrown
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var hasError = await hybridWebView.EvaluateJavaScriptAsync("HasError()");
96+
Assert.Contains("false", hasError, StringComparison.Ordinal);
97+
});
98+
99+
private class TestExceptionMethods
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{
101+
public string? LastMethodCalled { get; private set; }
102+
103+
public void ThrowException()
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{
105+
LastMethodCalled = nameof(ThrowException);
106+
throw new InvalidOperationException("Test exception message");
107+
}
108+
109+
public void ThrowCustomException()
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{
111+
LastMethodCalled = nameof(ThrowCustomException);
112+
throw new ArgumentException("Custom argument exception");
113+
}
114+
115+
public async Task ThrowExceptionAsync()
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{
117+
LastMethodCalled = nameof(ThrowExceptionAsync);
118+
await Task.Delay(10); // Make it actually async
119+
throw new InvalidOperationException("Async test exception");
120+
}
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122+
public string SuccessMethod()
123+
{
124+
LastMethodCalled = nameof(SuccessMethod);
125+
return "Success!";
126+
}
127+
}
128+
}

‎src/Controls/tests/DeviceTests/Resources/Raw/HybridTestRoot/exception-tests.html‎

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<!DOCTYPE html>
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<html lang="en" xmlns="http://www.w3.org/1999/xhtml">
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<head>
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<meta charset="utf-8" />
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<title></title>
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<link rel="icon" href="data:,">
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<script src="_framework/hybridwebview.js"></script>
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<script>
10+
window.addEventListener(
11+
"HybridWebViewMessageReceived",
12+
async function (e) {
13+
var methodToInvoke = e.detail.message;
14+
var result = null;
15+
var error = null;
16+
var hasError = false;
17+
18+
try {
19+
// Invoke the requested method
20+
result = await window.HybridWebView.InvokeDotNet(methodToInvoke);
21+
} catch (ex) {
22+
hasError = true;
23+
error = {
24+
message: ex.message,
25+
type: ex.dotNetErrorType || ex.name,
26+
stackTrace: ex.dotNetStackTrace || ex.stack
27+
};
28+
console.error('Caught exception from .NET method:', ex);
29+
}
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31+
// Store the results so they can be checked in the test
32+
lastResult = result;
33+
lastError = error;
34+
lastHasError = hasError;
35+
SetStatusDone();
36+
});
37+
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var lastResult = null;
39+
var lastError = null;
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var lastHasError = false;
41+
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function GetLastResult() {
43+
return lastResult === null ? null : JSON.stringify(lastResult);
44+
}
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function GetLastError() {
47+
return lastError ? lastError.message : null;
48+
}
49+
50+
function GetLastErrorType() {
51+
return lastError ? lastError.type : null;
52+
}
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54+
function GetLastErrorMessage() {
55+
return lastError ? lastError.message : null;
56+
}
57+
58+
function HasError() {
59+
return lastHasError.toString();
60+
}
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function SetStatusDone() {
63+
document.getElementById('status').innerHTML = "Done!";
64+
}
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66+
</script>
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</head>
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<body>
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<div>
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Hybrid exception test!
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</div>
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<div id="htmlLoaded"></div>
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<div id="status"></div>
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</body>
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</html>

‎src/Core/src/Handlers/HybridWebView/HybridWebView.js‎

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154154
if (!response) {
155155
return null;
156156
}
157+
// Check if the response indicates an error
158+
if (response.IsError) {
159+
const error = new Error(response.ErrorMessage || 'Unknown error occurred in .NET method');
160+
if (response.ErrorType) {
161+
error.dotNetErrorType = response.ErrorType;
162+
}
163+
if (response.ErrorStackTrace) {
164+
error.dotNetStackTrace = response.ErrorStackTrace;
165+
}
166+
throw error;
167+
}
157168
if (response.IsJson) {
158169
return JSON.parse(response.Result);
159170
}

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