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Some clarifications for ListView constructors (#10907)

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Ian Hickson 2017-06-23 14:06:18 -07:00 committed by GitHub
parent 9a6a3e1e27
commit ba520e7078
1 changed files with 16 additions and 6 deletions
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22
packages/flutter/lib/src/widgets/scroll_view.dart
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@ -438,6 +438,9 @@ class ListView extends BoxScrollView {
/// children because constructing the [List] requires doing work for every
/// child that could possibly be displayed in the list view instead of just
/// those children that are actually visible.
///
/// It is usually more efficient to create children on demand using [new
/// ListView.builder].
ListView({
Key key,
Axis scrollDirection: Axis.vertical,
@ -466,11 +469,18 @@ class ListView extends BoxScrollView {
/// number of children because the builder is called only for those children
/// that are actually visible.
///
/// Providing a non-null [itemCount] improves the ability of the [ListView] to
/// Providing a non-null `itemCount` improves the ability of the [ListView] to
/// estimate the maximum scroll extent.
///
/// [itemBuilder] will be called only with indices greater than or equal to
/// zero and less than [itemCount].
/// The `itemBuilder` callback will be called only with indices greater than
/// or equal to zero and less than `itemCount`.
///
/// The `itemBuilder` should actually create the widget instances when called.
/// Avoid using a builder that returns a previously-constructed widget; if the
/// list view's children are created in advance, or all at once when the
/// [ListView] itself is created, it is more efficient to use [new ListView].
/// Even more efficient, however, is to create the instances on demand using
/// this constructor's `itemBuilder` callback.
ListView.builder({
Key key,
Axis scrollDirection: Axis.vertical,
@ -623,11 +633,11 @@ class GridView extends BoxScrollView {
/// number of children because the builder is called only for those children
/// that are actually visible.
///
/// Providing a non-null [itemCount] improves the ability of the [GridView] to
/// Providing a non-null `itemCount` improves the ability of the [GridView] to
/// estimate the maximum scroll extent.
///
/// [itemBuilder] will be called only with indices greater than or equal to
/// zero and less than [itemCount].
/// `itemBuilder` will be called only with indices greater than or equal to
/// zero and less than `itemCount`.
///
/// The [gridDelegate] argument must not be null.
GridView.builder({