今天暂时把源码给粘贴出来，将来会详细的学习和整理。
源码的位置：react-native/Libraries/Lists/FlatList.js
const Platform = require('../Utilities/Platform');
const deepDiffer = require('../Utilities/differ/deepDiffer');
const React = require('react');
const View = require('../Components/View/View');
const VirtualizedList = require('./VirtualizedList');
const StyleSheet = require('../StyleSheet/StyleSheet');
const invariant = require('invariant');
import {type ScrollResponderType} from '../Components/ScrollView/ScrollView';
import type {ScrollViewNativeComponentType} from '../Components/ScrollView/ScrollViewNativeComponentType.js';
import type {ViewStyleProp} from '../StyleSheet/StyleSheet';
import type {
ViewToken,
ViewabilityConfigCallbackPair,
} from './ViewabilityHelper';
import type {RenderItemType, RenderItemProps} from './VirtualizedList';
type RequiredProps<ItemT> = {|
/**
* For simplicity, data is just a plain array. If you want to use something else, like an
* immutable list, use the underlying `VirtualizedList` directly.
*/
data: ?$ReadOnlyArray<ItemT>,
|};
type OptionalProps<ItemT> = {|
/**
* Takes an item from `data` and renders it into the list. Example usage:
*
* <FlatList
* ItemSeparatorComponent={Platform.OS !== 'android' && ({highlighted}) => (
* <View style={[style.separator, highlighted && {marginLeft: 0}]} />
* )}
* data={[{title: 'Title Text', key: 'item1'}]}
* renderItem={({item, separators}) => (
* <TouchableHighlight
* onPress={() => this._onPress(item)}
* onShowUnderlay={separators.highlight}
* onHideUnderlay={separators.unhighlight}>
* <View style={{backgroundColor: 'white'}}>
* <Text>{item.title}</Text>
* </View>
* </TouchableHighlight>
* )}
* />
*
* Provides additional metadata like `index` if you need it, as well as a more generic
* `separators.updateProps` function which let's you set whatever props you want to change the
* rendering of either the leading separator or trailing separator in case the more common
* `highlight` and `unhighlight` (which set the `highlighted: boolean` prop) are insufficient for
* your use-case.
*/
renderItem?: ?RenderItemType<ItemT>,
/**
* Optional custom style for multi-item rows generated when numColumns > 1.
*/
columnWrapperStyle?: ViewStyleProp,
/**
* A marker property for telling the list to re-render (since it implements `PureComponent`). If
* any of your `renderItem`, Header, Footer, etc. functions depend on anything outside of the
* `data` prop, stick it here and treat it immutably.
*/
extraData?: any,
/**
* `getItemLayout` is an optional optimizations that let us skip measurement of dynamic content if
* you know the height of items a priori. `getItemLayout` is the most efficient, and is easy to
* use if you have fixed height items, for example:
*
* getItemLayout={(data, index) => (
* {length: ITEM_HEIGHT, offset: ITEM_HEIGHT * index, index}
* )}
*
* Adding `getItemLayout` can be a great performance boost for lists of several hundred items.
* Remember to include separator length (height or width) in your offset calculation if you
* specify `ItemSeparatorComponent`.
*/
getItemLayout?: (
data: ?Array<ItemT>,
index: number,
) => {
length: number,
offset: number,
index: number,
...
},
/**
* If true, renders items next to each other horizontally instead of stacked vertically.
*/
horizontal?: ?boolean,
/**
* How many items to render in the initial batch. This should be enough to fill the screen but not
* much more. Note these items will never be unmounted as part of the windowed rendering in order
* to improve perceived performance of scroll-to-top actions.
*/
initialNumToRender: number,
/**
* Instead of starting at the top with the first item, start at `initialScrollIndex`. This
* disables the "scroll to top" optimization that keeps the first `initialNumToRender` items
* always rendered and immediately renders the items starting at this initial index. Requires
* `getItemLayout` to be implemented.
*/
initialScrollIndex?: ?number,
/**
* Reverses the direction of scroll. Uses scale transforms of -1.
*/
inverted?: ?boolean,
/**
* Used to extract a unique key for a given item at the specified index. Key is used for caching
* and as the react key to track item re-ordering. The default extractor checks `item.key`, then
* falls back to using the index, like React does.
*/
keyExtractor: (item: ItemT, index: number) => string,
/**
* Multiple columns can only be rendered with `horizontal={false}` and will zig-zag like a
* `flexWrap` layout. Items should all be the same height - masonry layouts are not supported.
*/
numColumns: number,
/**
* See `ScrollView` for flow type and further documentation.
*/
fadingEdgeLength?: ?number,
|};
type FlatListProps<ItemT> = {|
...RequiredProps<ItemT>,
...OptionalProps<ItemT>,
|};
type VirtualizedListProps = React.ElementConfig<typeof VirtualizedList>;
export type Props<ItemT> = {
...$Diff<
VirtualizedListProps,
{
getItem: $PropertyType<VirtualizedListProps, 'getItem'>,
getItemCount: $PropertyType<VirtualizedListProps, 'getItemCount'>,
getItemLayout: $PropertyType<VirtualizedListProps, 'getItemLayout'>,
renderItem: $PropertyType<VirtualizedListProps, 'renderItem'>,
keyExtractor: $PropertyType<VirtualizedListProps, 'keyExtractor'>,
...
},
>,
...FlatListProps<ItemT>,
...
};
const defaultProps = {
...VirtualizedList.defaultProps,
numColumns: 1,
/**
* Enabling this prop on Android greatly improves scrolling performance with no known issues.
* The alternative is that scrolling on Android is unusably bad. Enabling it on iOS has a few
* known issues.
*/
removeClippedSubviews: Platform.OS === 'android',
};
export type DefaultProps = typeof defaultProps;
/**
* A performant interface for rendering simple, flat lists, supporting the most handy features:
*
* - Fully cross-platform.
* - Optional horizontal mode.
* - Configurable viewability callbacks.
* - Header support.
* - Footer support.
* - Separator support.
* - Pull to Refresh.
* - Scroll loading.
* - ScrollToIndex support.
*
* If you need section support, use [`<SectionList>`](docs/sectionlist.html).
*
* Minimal Example:
*
* <FlatList
* data={[{key: 'a'}, {key: 'b'}]}
* renderItem={({item}) => <Text>{item.key}</Text>}
* />
*
* More complex, multi-select example demonstrating `PureComponent` usage for perf optimization and avoiding bugs.
*
* - By binding the `onPressItem` handler, the props will remain `===` and `PureComponent` will
* prevent wasteful re-renders unless the actual `id`, `selected`, or `title` props change, even
* if the components rendered in `MyListItem` did not have such optimizations.
* - By passing `extraData={this.state}` to `FlatList` we make sure `FlatList` itself will re-render
* when the `state.selected` changes. Without setting this prop, `FlatList` would not know it
* needs to re-render any items because it is also a `PureComponent` and the prop comparison will
* not show any changes.
* - `keyExtractor` tells the list to use the `id`s for the react keys instead of the default `key` property.
*
*
* class MyListItem extends React.PureComponent {
* _onPress = () => {
* this.props.onPressItem(this.props.id);
* };
*
* render() {
* const textColor = this.props.selected ? "red" : "black";
* return (
* <TouchableOpacity onPress={this._onPress}>
* <View>
* <Text style={{ color: textColor }}>
* {this.props.title}
* </Text>
* </View>
* </TouchableOpacity>
* );
* }
* }
*
* class MultiSelectList extends React.PureComponent {
* state = {selected: (new Map(): Map<string, boolean>)};
*
* _keyExtractor = (item, index) => item.id;
*
* _onPressItem = (id: string) => {
* // updater functions are preferred for transactional updates
* this.setState((state) => {
* // copy the map rather than modifying state.
* const selected = new Map(state.selected);
* selected.set(id, !selected.get(id)); // toggle
* return {selected};
* });
* };
*
* _renderItem = ({item}) => (
* <MyListItem
* id={item.id}
* onPressItem={this._onPressItem}
* selected={!!this.state.selected.get(item.id)}
* title={item.title}
* />
* );
*
* render() {
* return (
* <FlatList
* data={this.props.data}
* extraData={this.state}
* keyExtractor={this._keyExtractor}
* renderItem={this._renderItem}
* />
* );
* }
* }
*
* This is a convenience wrapper around [`<VirtualizedList>`](docs/virtualizedlist.html),
* and thus inherits its props (as well as those of `ScrollView`) that aren't explicitly listed
* here, along with the following caveats:
*
* - Internal state is not preserved when content scrolls out of the render window. Make sure all
* your data is captured in the item data or external stores like Flux, Redux, or Relay.
* - This is a `PureComponent` which means that it will not re-render if `props` remain shallow-
* equal. Make sure that everything your `renderItem` function depends on is passed as a prop
* (e.g. `extraData`) that is not `===` after updates, otherwise your UI may not update on
* changes. This includes the `data` prop and parent component state.
* - In order to constrain memory and enable smooth scrolling, content is rendered asynchronously
* offscreen. This means it's possible to scroll faster than the fill rate ands momentarily see
* blank content. This is a tradeoff that can be adjusted to suit the needs of each application,
* and we are working on improving it behind the scenes.
* - By default, the list looks for a `key` prop on each item and uses that for the React key.
* Alternatively, you can provide a custom `keyExtractor` prop.
*
* Also inherits [ScrollView Props](docs/scrollview.html#props), unless it is nested in another FlatList of same orientation.
*/
class FlatList<ItemT> extends React.PureComponent<Props<ItemT>, void> {
static defaultProps: DefaultProps = defaultProps;
props: Props<ItemT>;
/**
* Scrolls to the end of the content. May be janky without `getItemLayout` prop.
*/
scrollToEnd(params?: ?{animated?: ?boolean, ...}) {
if (this._listRef) {
this._listRef.scrollToEnd(params);
}
}
/**
* Scrolls to the item at the specified index such that it is positioned in the viewable area
* such that `viewPosition` 0 places it at the top, 1 at the bottom, and 0.5 centered in the
* middle. `viewOffset` is a fixed number of pixels to offset the final target position.
*
* Note: cannot scroll to locations outside the render window without specifying the
* `getItemLayout` prop.
*/
scrollToIndex(params: {
animated?: ?boolean,
index: number,
viewOffset?: number,
viewPosition?: number,
...
}) {
if (this._listRef) {
this._listRef.scrollToIndex(params);
}
}
/**
* Requires linear scan through data - use `scrollToIndex` instead if possible.
*
* Note: cannot scroll to locations outside the render window without specifying the
* `getItemLayout` prop.
*/
scrollToItem(params: {
animated?: ?boolean,
item: ItemT,
viewPosition?: number,
...
}) {
if (this._listRef) {
this._listRef.scrollToItem(params);
}
}
/**
* Scroll to a specific content pixel offset in the list.
*
* Check out [scrollToOffset](docs/virtualizedlist.html#scrolltooffset) of VirtualizedList
*/
scrollToOffset(params: {animated?: ?boolean, offset: number, ...}) {
if (this._listRef) {
this._listRef.scrollToOffset(params);
}
}
/**
* Tells the list an interaction has occurred, which should trigger viewability calculations, e.g.
* if `waitForInteractions` is true and the user has not scrolled. This is typically called by
* taps on items or by navigation actions.
*/
recordInteraction() {
if (this._listRef) {
this._listRef.recordInteraction();
}
}
/**
* Displays the scroll indicators momentarily.
*
* @platform ios
*/
flashScrollIndicators() {
if (this._listRef) {
this._listRef.flashScrollIndicators();
}
}
/**
* Provides a handle to the underlying scroll responder.
*/
getScrollResponder(): ?ScrollResponderType {
if (this._listRef) {
return this._listRef.getScrollResponder();
}
}
/**
* Provides a reference to the underlying host component
*/
getNativeScrollRef():
| ?React.ElementRef<typeof View>
| ?React.ElementRef<ScrollViewNativeComponentType> {
if (this._listRef) {
return this._listRef.getScrollRef();
}
}
getScrollableNode(): any {
if (this._listRef) {
return this._listRef.getScrollableNode();
}
}
setNativeProps(props: {[string]: mixed, ...}) {
if (this._listRef) {
this._listRef.setNativeProps(props);
}
}
constructor(props: Props<ItemT>) {
super(props);
this._checkProps(this.props);
if (this.props.viewabilityConfigCallbackPairs) {
this._virtualizedListPairs = this.props.viewabilityConfigCallbackPairs.map(
pair => ({
viewabilityConfig: pair.viewabilityConfig,
onViewableItemsChanged: this._createOnViewableItemsChanged(
pair.onViewableItemsChanged,
),
}),
);
} else if (this.props.onViewableItemsChanged) {
this._virtualizedListPairs.push({
/* $FlowFixMe(>=0.63.0 site=react_native_fb) This comment suppresses an
* error found when Flow v0.63 was deployed. To see the error delete
* this comment and run Flow. */
viewabilityConfig: this.props.viewabilityConfig,
onViewableItemsChanged: this._createOnViewableItemsChanged(
this.props.onViewableItemsChanged,
),
});
}
}
componentDidUpdate(prevProps: Props<ItemT>) {
invariant(
prevProps.numColumns === this.props.numColumns,
'Changing numColumns on the fly is not supported. Change the key prop on FlatList when ' +
'changing the number of columns to force a fresh render of the component.',
);
invariant(
prevProps.onViewableItemsChanged === this.props.onViewableItemsChanged,
'Changing onViewableItemsChanged on the fly is not supported',
);
invariant(
!deepDiffer(prevProps.viewabilityConfig, this.props.viewabilityConfig),
'Changing viewabilityConfig on the fly is not supported',
);
invariant(
prevProps.viewabilityConfigCallbackPairs ===
this.props.viewabilityConfigCallbackPairs,
'Changing viewabilityConfigCallbackPairs on the fly is not supported',
);
this._checkProps(this.props);
}
_listRef: ?React.ElementRef<typeof VirtualizedList>;
_virtualizedListPairs: Array<ViewabilityConfigCallbackPair> = [];
_captureRef = ref => {
this._listRef = ref;
};
_checkProps(props: Props<ItemT>) {
const {
// $FlowFixMe this prop doesn't exist, is only used for an invariant
getItem,
// $FlowFixMe this prop doesn't exist, is only used for an invariant
getItemCount,
horizontal,
numColumns,
columnWrapperStyle,
onViewableItemsChanged,
viewabilityConfigCallbackPairs,
} = props;
invariant(
!getItem && !getItemCount,
'FlatList does not support custom data formats.',
);
if (numColumns > 1) {
invariant(!horizontal, 'numColumns does not support horizontal.');
} else {
invariant(
!columnWrapperStyle,
'columnWrapperStyle not supported for single column lists',
);
}
invariant(
!(onViewableItemsChanged && viewabilityConfigCallbackPairs),
'FlatList does not support setting both onViewableItemsChanged and ' +
'viewabilityConfigCallbackPairs.',
);
}
_getItem = (data: Array<ItemT>, index: number) => {
const {numColumns} = this.props;
if (numColumns > 1) {
const ret = [];
for (let kk = 0; kk < numColumns; kk++) {
const item = data[index * numColumns + kk];
if (item != null) {
ret.push(item);
}
}
return ret;
} else {
return data[index];
}
};
_getItemCount = (data: ?Array<ItemT>): number => {
if (data) {
const {numColumns} = this.props;
return numColumns > 1 ? Math.ceil(data.length / numColumns) : data.length;
} else {
return 0;
}
};
_keyExtractor = (items: ItemT | Array<ItemT>, index: number) => {
const {keyExtractor, numColumns} = this.props;
if (numColumns > 1) {
invariant(
Array.isArray(items),
'FlatList: Encountered internal consistency error, expected each item to consist of an ' +
'array with 1-%s columns; instead, received a single item.',
numColumns,
);
return items
.map((it, kk) => keyExtractor(it, index * numColumns + kk))
.join(':');
} else {
// $FlowFixMe Can't call keyExtractor with an array
return keyExtractor(items, index);
}
};
_pushMultiColumnViewable(arr: Array<ViewToken>, v: ViewToken): void {
const {numColumns, keyExtractor} = this.props;
v.item.forEach((item, ii) => {
invariant(v.index != null, 'Missing index!');
const index = v.index * numColumns + ii;
arr.push({...v, item, key: keyExtractor(item, index), index});
});
}
_createOnViewableItemsChanged(
onViewableItemsChanged: ?(info: {
viewableItems: Array<ViewToken>,
changed: Array<ViewToken>,
...
}) => void,
) {
return (info: {
viewableItems: Array<ViewToken>,
changed: Array<ViewToken>,
...
}) => {
const {numColumns} = this.props;
if (onViewableItemsChanged) {
if (numColumns > 1) {
const changed = [];
const viewableItems = [];
info.viewableItems.forEach(v =>
this._pushMultiColumnViewable(viewableItems, v),
);
info.changed.forEach(v => this._pushMultiColumnViewable(changed, v));
onViewableItemsChanged({viewableItems, changed});
} else {
onViewableItemsChanged(info);
}
}
};
}
_renderer = () => {
const {
ListItemComponent,
renderItem,
numColumns,
columnWrapperStyle,
} = this.props;
let virtualizedListRenderKey = ListItemComponent
? 'ListItemComponent'
: 'renderItem';
const renderer = (props): React.Node => {
if (ListItemComponent) {
// $FlowFixMe Component isn't valid
return <ListItemComponent {...props} />;
} else if (renderItem) {
return renderItem(props);
} else {
return null;
}
};
return {
/* $FlowFixMe(>=0.111.0 site=react_native_fb) This comment suppresses an
* error found when Flow v0.111 was deployed. To see the error, delete
* this comment and run Flow. */
[virtualizedListRenderKey]: (info: RenderItemProps<ItemT>) => {
if (numColumns > 1) {
const {item, index} = info;
invariant(
Array.isArray(item),
'Expected array of items with numColumns > 1',
);
return (
<View style={StyleSheet.compose(styles.row, columnWrapperStyle)}>
{item.map((it, kk) => {
const element = renderer({
item: it,
index: index * numColumns + kk,
separators: info.separators,
});
return element != null ? (
<React.Fragment key={kk}>{element}</React.Fragment>
) : null;
})}
</View>
);
} else {
return renderer(info);
}
},
};
};
render(): React.Node {
const {numColumns, columnWrapperStyle, ...restProps} = this.props;
return (
<VirtualizedList
{...restProps}
getItem={this._getItem}
getItemCount={this._getItemCount}
keyExtractor={this._keyExtractor}
ref={this._captureRef}
viewabilityConfigCallbackPairs={this._virtualizedListPairs}
{...this._renderer()}
/>
);
}
}
const styles = StyleSheet.create({
row: {flexDirection: 'row'},
});
module.exports = FlatList;
