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Add GC.KeepAlive to ComposeBridges JNI calls #11

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Merged
jonathanpeppers merged 1 commit into from
Jun 3, 2026
Merged

Add GC.KeepAlive to ComposeBridges JNI calls #11

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27 changes: 27 additions & 0 deletions .github/copilot-instructions.md
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Original file line number Diff line number Diff line change
Expand Up @@ -122,6 +122,33 @@ Pattern, copied throughout the file:
`try`/`finally` that calls `DeleteLocalRef`.
6. Pass managed objects as `((Java.Lang.Object)obj).Handle`. Use
`IntPtr.Zero` for `null`.
7. **Always wrap `JNIEnv.CallStatic*Method` in `try { … } finally { … }`
and call `GC.KeepAlive(...)` on every managed parameter whose
`.Handle` was read into a `JValue` (lambdas, the composer, optional
slot wrappers — `null` is a no-op so unconditional `KeepAlive` on
nullable params is fine).** This matches what
`dotnet/java-interop` generates for bound members. Without it, the
JIT considers each managed wrapper dead the instant `.Handle` is
read, and a GC during the JNI call can finalize the wrapper and
invalidate the underlying handle. Combine with the `DeleteLocalRef`
`finally` for string args — one `try`/`finally` doing both is the
normal shape.

Pattern:
```csharp
JValue* args = stackalloc JValue[N];
// fill args ...
try
{
JNIEnv.CallStaticVoidMethod(s_cls, s_method, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(content);
GC.KeepAlive(composer);
}
```

Keep these methods `internal` — user code never touches JNI directly.
**Do not add new JNI bridges if the binding already exposes the
Expand Down
167 changes: 153 additions & 14 deletions src/ComposeNet.Compose/ComposeBridges.cs
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Original file line number Diff line number Diff line change
Expand Up @@ -70,6 +70,7 @@ public static unsafe void Text(string text, IComposer composer)
finally
{
JNIEnv.DeleteLocalRef(textRef);
GC.KeepAlive(composer);
}
}

Expand Down Expand Up @@ -112,7 +113,16 @@ public static unsafe void Button(IFunction0 onClick, IFunction3 content, ICompos
args[10] = new JValue(((Java.Lang.Object)composer).Handle);
args[11] = new JValue(0);
args[12] = new JValue(defaults);
JNIEnv.CallStaticVoidMethod(s_buttonClass, s_buttonMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_buttonClass, s_buttonMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(content);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.IconButtonKt.IconButton(onClick, modifier,
Expand Down Expand Up @@ -144,7 +154,16 @@ public static unsafe void IconButton(IFunction0 onClick, IFunction2 content, ICo
args[6] = new JValue(((Java.Lang.Object)composer).Handle);
args[7] = new JValue(0);
args[8] = new JValue((int)IconButtonDefault.All);
JNIEnv.CallStaticVoidMethod(s_iconButtonClass, s_iconButtonMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_iconButtonClass, s_iconButtonMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(content);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.FloatingActionButtonKt.FloatingActionButton-X-z6DiA(
Expand Down Expand Up @@ -180,7 +199,16 @@ public static unsafe void FloatingActionButton(IFunction0 onClick, IFunction2 co
args[8] = new JValue(((Java.Lang.Object)composer).Handle);
args[9] = new JValue(0);
args[10] = new JValue((int)FloatingActionButtonDefault.All);
JNIEnv.CallStaticVoidMethod(s_fabClass, s_fabMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_fabClass, s_fabMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(content);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.SurfaceKt.Surface-T9BRK9s (non-interactive):
Expand Down Expand Up @@ -214,7 +242,15 @@ public static unsafe void Surface(IFunction2 content, IComposer composer)
args[8] = new JValue(((Java.Lang.Object)composer).Handle);
args[9] = new JValue(0);
args[10] = new JValue((int)SurfaceDefault.All);
JNIEnv.CallStaticVoidMethod(s_surfaceClass, s_surfaceMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_surfaceClass, s_surfaceMethod, args);
}
finally
{
GC.KeepAlive(content);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.TextFieldKt.TextField (String overload):
Expand Down Expand Up @@ -321,7 +357,20 @@ public static unsafe void AlertDialog(
args[15] = new JValue(0); // $changed
args[16] = new JValue(0); // $changed1
args[17] = new JValue(defaults); // $default
JNIEnv.CallStaticVoidMethod(s_alertDialogClass, s_alertDialogMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_alertDialogClass, s_alertDialogMethod, args);
}
finally
{
GC.KeepAlive(onDismissRequest);
GC.KeepAlive(confirmButton);
GC.KeepAlive(dismissButton);
GC.KeepAlive(icon);
GC.KeepAlive(title);
GC.KeepAlive(text);
GC.KeepAlive(composer);
}
}

static unsafe void InvokeTextField(IntPtr cls, IntPtr method, string value, IFunction1 onValueChange, IComposer composer, int defaults)
Expand Down Expand Up @@ -363,6 +412,8 @@ static unsafe void InvokeTextField(IntPtr cls, IntPtr method, string value, IFun
finally
{
JNIEnv.DeleteLocalRef(valueRef);
GC.KeepAlive(onValueChange);
GC.KeepAlive(composer);
}
}

Expand Down Expand Up @@ -397,7 +448,15 @@ public static unsafe void Card(IFunction3 content, IComposer composer)
args[6] = new JValue(((Java.Lang.Object)composer).Handle);
args[7] = new JValue(0);
args[8] = new JValue((int)CardDefault.All);
JNIEnv.CallStaticVoidMethod(s_cardClass, s_cardMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_cardClass, s_cardMethod, args);
}
finally
{
GC.KeepAlive(content);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.ChipKt.AssistChip:
Expand Down Expand Up @@ -449,7 +508,18 @@ public static unsafe void AssistChip(
args[12] = new JValue(0); // $changed
args[13] = new JValue(0); // $changed1
args[14] = new JValue(defaults); // $default
JNIEnv.CallStaticVoidMethod(s_assistChipClass, s_assistChipMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_assistChipClass, s_assistChipMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(label);
GC.KeepAlive(leadingIcon);
GC.KeepAlive(trailingIcon);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.ChipKt.FilterChip:
Expand Down Expand Up @@ -503,7 +573,18 @@ public static unsafe void FilterChip(
args[13] = new JValue(0);
args[14] = new JValue(0);
args[15] = new JValue(defaults);
JNIEnv.CallStaticVoidMethod(s_filterChipClass, s_filterChipMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_filterChipClass, s_filterChipMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(label);
GC.KeepAlive(leadingIcon);
GC.KeepAlive(trailingIcon);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.ChipKt.InputChip:
Expand Down Expand Up @@ -559,7 +640,19 @@ public static unsafe void InputChip(
args[14] = new JValue(0);
args[15] = new JValue(0);
args[16] = new JValue(defaults);
JNIEnv.CallStaticVoidMethod(s_inputChipClass, s_inputChipMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_inputChipClass, s_inputChipMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(label);
GC.KeepAlive(leadingIcon);
GC.KeepAlive(avatar);
GC.KeepAlive(trailingIcon);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.ChipKt.SuggestionChip:
Expand Down Expand Up @@ -605,7 +698,17 @@ public static unsafe void SuggestionChip(
args[10] = new JValue(((Java.Lang.Object)composer).Handle);
args[11] = new JValue(0);
args[12] = new JValue(defaults);
JNIEnv.CallStaticVoidMethod(s_suggestionChipClass, s_suggestionChipMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_suggestionChipClass, s_suggestionChipMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(label);
GC.KeepAlive(icon);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.NavigationBarKt.NavigationBar-HsRjFd4:
Expand Down Expand Up @@ -638,7 +741,15 @@ public static unsafe void NavigationBar(IFunction3 content, IComposer composer)
args[6] = new JValue(((Java.Lang.Object)composer).Handle);
args[7] = new JValue(0);
args[8] = new JValue((int)NavigationBarDefault.All);
JNIEnv.CallStaticVoidMethod(s_navBarClass, s_navBarMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_navBarClass, s_navBarMethod, args);
}
finally
{
GC.KeepAlive(content);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.NavigationBarKt.NavigationBarItem:
Expand Down Expand Up @@ -691,7 +802,17 @@ public static unsafe void NavigationBarItem(
args[10] = new JValue(((Java.Lang.Object)composer).Handle);
args[11] = new JValue(0);
args[12] = new JValue(defaults);
JNIEnv.CallStaticVoidMethod(s_navBarItemClass, s_navBarItemMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_navBarItemClass, s_navBarItemMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(icon);
GC.KeepAlive(label);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.NavigationRailKt.NavigationRail-qi6gXK8:
Expand Down Expand Up @@ -726,7 +847,15 @@ public static unsafe void NavigationRail(IFunction3 content, IComposer composer)
args[6] = new JValue(((Java.Lang.Object)composer).Handle);
args[7] = new JValue(0);
args[8] = new JValue((int)NavigationRailDefault.All);
JNIEnv.CallStaticVoidMethod(s_navRailClass, s_navRailMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_navRailClass, s_navRailMethod, args);
}
finally
{
GC.KeepAlive(content);
GC.KeepAlive(composer);
}
}

// androidx.compose.material3.NavigationRailKt.NavigationRailItem:
Expand Down Expand Up @@ -773,6 +902,16 @@ public static unsafe void NavigationRailItem(
args[9] = new JValue(((Java.Lang.Object)composer).Handle);
args[10] = new JValue(0);
args[11] = new JValue(defaults);
JNIEnv.CallStaticVoidMethod(s_navRailItemClass, s_navRailItemMethod, args);
try
{
JNIEnv.CallStaticVoidMethod(s_navRailItemClass, s_navRailItemMethod, args);
}
finally
{
GC.KeepAlive(onClick);
GC.KeepAlive(icon);
GC.KeepAlive(label);
GC.KeepAlive(composer);
}
}
}