Summary:
When mutation of a stack happens, we'd like to compute the diff of the stacks (before and after) so that
we can know which routes are removed in the new stack.
This diff adds a new method `substract` which does what we need.
Summary:
# Summary
Add a method `keyOf` to NavigationRouteStack.
The method `keyOf` returns a key that is associated with the route.
The a route is added to a stack, the stack creats an unique key for it and
will keep the key for the route until the route is rmeoved from the stack.
The stack also passes the keys to its derived stack (the new stack created by the
mutation API such as `push`, `pop`...etc).
The key for the route persists until the initial stack and its derived stack no longer
contains this route.
# Why Do We Need This?
Navigator has needs to use an unique key to manage the scenes rendered.
The problem is that `route` itself isn't a very reliable thing to be used as the key.
Consider this example:
```
// `scene_1` animates into the viewport.
navigator.push('scene_1');
setTimeout(() => {
// `scene_1` animates off the viewport.
navigator.pop();
}, 100);
setTimeout(() => {
// Should we bring in a new scene or bring back the one that was previously popped?
navigator.push('scene_1');
}, 200);
```
Because we currently use `route` itself as a key for the scene, we'd have to block a route
until its scene is completely off the components tree even the route itself is no longer
in the stack otherwise we'd see strange animation of jumping scenes.
# What's Next
We're hoping that we can build pure reactive view for NavigationRouteStack easily.
The naive implementation of NavigationRouteStackView may look like this:
```
class NavigationRouteStackView {
constructor() {
this.state = {
staleScenes: {},
};
}
componentWillReceiveProps(nextProps) {
if (nextProps.stack !== this.props.stack) {
var stale;
var staleScenes = {...this.state.staleScenes};
this.props.stack.forEach((route, index, key) => {
if (nextProps.stack.keyOf(route) !== key) {
stale = true;
staleScenes[key] = {route, index, key, stale};
}
});
if (stale) {
this.setState({
staleScenes,
});
}
}
}
render() {
var scenes = [];
this.props.stack.forEach((route, index, key) => {
scenes.push({route, index, key});
});
Object.keys(this.state.staleScenes).forEach(key => {
scenes.push(this.state.staleScenes[key]);
});
scenes.sort(stableSortByIndex);
return <View>{scenes.map(renderScene)}</View>;
}
}
```
Summary:
While adeveloper requests the emitter to emit an event, the emitter
may not emit the event immediately instead of putting the request
into a queue and process it later.
This diff allows the developer to provide a callback which will be called
when the event has been emitted.
For instance:
```
class NavigationContext {
push(nextRoute) {
var nextStack = this._stack.push(nextRoute);
this.emit(
'change',
{
reason: 'push',
nextStack: nextStack,
nextRoute: nextRoute,
},
this._onPush
);
}
_onPush(event){
if (event.defaultPrevented) {
return;
}
this._stack = event.nextStack;
this.emit('change');
}
}
```
Summary:
Introducing the data structure NavigationRouteStack that focused on managing
navigation routes stack.
The goal is to make <Navigatior /> thinner by moving stack management logic into
its own class and make sure it's well-tested.
Teh next step will be cleaning up <Navigatior /> and add `NavigationRouteStack` to
`NavigationContext`.
of the navigator component.
Summary:
Per offline discussion with @evv, we'd like to deprecate the `onDidFocus` and `onWillFocus`
API that makes it really hard for the descendent children of a navigator to observe its focus
change events.
@public
Since for now the descendent children do have access to the navigator via `this.props.navigator`,
this diff makes it easy to observe the focus change event by doing:
```
this.props.navigator.addListener('willfocus', this._onFocus);
```
The goal is to make the event system in navigator more useful and maintainable.
Test Plan:
Test Video: https://www.facebook.com/pxlcld/mrzS
1. jest: ./Libraries/FBReactKit/js/runTests.js NavigationEventEmitter
2. Load UI Explorer: <Navigator />, see console logs that shows the focus change events fires.
