Callbacks and Lifetime

Most PixelUI callbacks use ETL inline storage:

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using InputCallback = etl::inplace_function<bool(InputEvent), CALLBACK_STORAGE_SIZE>;
using VoidCallback  = etl::inplace_function<void(), CALLBACK_STORAGE_SIZE>;
using ValueCallback = etl::inplace_function<void(int32_t), CALLBACK_STORAGE_SIZE>;

This avoids std::function and ordinary heap allocation for individual callbacks, but it does not solve the lifetime of captured objects.

Recommended App member capture

void onEnter(ExitCallback cb) override {
    IApplication::onEnter(cb);
    button_.setCallback([this]() {
        value_++;
        ui_.markDirty();
    });
    ui_.addWidgetToFocusManager(&button_);
}

This capture is valid only while the Widget callback cannot outlive its App. See App lifecycle and ViewManager for the unified cleanup order before destruction.

Common mistake

void configure() {
    int temporary = 42;
    button_.setCallback([&temporary]() {
        use(temporary); // dangling after configure() returns
    });
}

Likewise, do not pass a local character array to a Widget or Popup and then return, queue a reference to a local numeric value, or retain a pointer from getCurrentApp() across a pop.

Inline capacity

A large lambda may fail to fit in etl::inplace_function at compile time. Instead of globally increasing the capacity, it is usually better to capture only this, a pointer, or a small ID. See Resource limits for the configured size.

Member declaration order

C++ destroys members in reverse declaration order. If a Widget holds a non-owning reference to a buffer or state object, declare that object before the Widget. See Widgets and Focus for a Chart example.