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# Fragment
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Fragment is a concept copied from [Android](https://developer.android.com/guide/fragments).
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It represents a reusable portion of your app's UI. A fragment defines and manages its own layout, has its own lifecycle,
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and can handle its own events. Like Android's Fragment that must be hosted by an activity or another fragment, Fragment
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in LVGL needs to be hosted by an object, or another fragment. The fragment’s view hierarchy becomes part of, or attaches
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to, the host’s view hierarchy.
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Such concept also has some similarities
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to [UiViewController on iOS](https://developer.apple.com/documentation/uikit/uiviewcontroller).
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Fragment Manager is a manager holding references to fragments attached to it, and has an internal stack to achieve
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navigation. You can use fragment manager to build navigation stack, or multi pane application easily.
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## Usage
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Enable `LV_USE_FRAGMENT` in `lv_conf.h`.
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### Create Fragment Class
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```c
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struct sample_fragment_t {
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/* IMPORTANT: don't miss this part */
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lv_fragment_t base;
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/* States, object references and data fields for this fragment */
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const char *title;
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};
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const lv_fragment_class_t sample_cls = {
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/* Initialize something needed */
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.constructor_cb = sample_fragment_ctor,
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/* Create view objects */
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.create_obj_cb = sample_fragment_create_obj,
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/* IMPORTANT: size of your fragment struct */
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.instance_size = sizeof(struct sample_fragment_t)
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};
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```
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### Use `lv_fragment_manager`
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```c
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/* Create fragment instance, and objects will be added to container */
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lv_fragment_manager_t *manager = lv_fragment_manager_create(container, NULL);
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/* Replace current fragment with instance of sample_cls, and init_argument is user defined pointer */
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lv_fragment_manager_replace(manager, &sample_cls, init_argument);
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```
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### Fragment Based Navigation
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```c
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/* Add one instance into manager stack. View object of current fragment will be destroyed,
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* but instances created in class constructor will be kept.
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*/
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lv_fragment_manager_push(manager, &sample_cls, NULL);
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/* Remove the top most fragment from the stack, and bring back previous one. */
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lv_fragment_manager_pop(manager);
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```
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## Example
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```eval_rst
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.. include:: ../../examples/others/fragment/index.rst
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```
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## API
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```eval_rst
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.. doxygenfile:: lv_fragment.h
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:project: lvgl
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```
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