-
external声明方法实现方式
@patch
class 类名 {
...
@patch
external声明的方法名
...
}
external声明的方法,通过@patch注解实现
external关键字介绍请移步flutter external关键字详解
-
external声明方法实现文件路径
移动端external声明方法实现在vm目录下:
flutter sdk目录/bin/cache/dart-sdk/lib/_internal/vm/lib
web端external声明方法实现在js_runtime目录下:
flutter sdk目录/bin/cache/dart-sdk/lib/_internal/js_runtime/lib
-
external声明方法实现文件命名
external方法的实现文件一般命名为xxx_patch.dart,如在vm/lib目录下,可以看到各种xxx_patch.dart文件:
patch文件.png
-
external声明方法实现文件查找
可以在终端通过grep搜索命令找到对应类里external方法实现的xxx_patch.dart文件:
grep -n "class 类名" -r ./* --color=auto
以查找Object类里external方法的实现为例:
1、Object类定义如下:
class Object {
const Object();
external bool operator ==(other);
external int get hashCode;
external String toString();
@pragma("vm:entry-point")
external dynamic noSuchMethod(Invocation invocation);
external Type get runtimeType;
}
可以看到Object类里有很多方法都是用external声明
2、在flutter sdk目录/bin/cache/dart-sdk/lib/_internal目录下,执行查找class Object命令:
grep -n "class Object" -r ./* --color=auto
查找Object.png
由此可知:web端Object实现文件是./js_runtime/lib/core_patch.dart
移动端Object实现文件是./vm/lib/object_patch.dart
打开web端Object实现文件./js_runtime/lib/core_patch.dart,如下:
// Patch for Object implementation.
@patch
class Object {
@patch
bool operator ==(Object other) => identical(this, other);
@patch
int get hashCode => Primitives.objectHashCode(this);
@patch
String toString() => Primitives.objectToHumanReadableString(this);
@patch
dynamic noSuchMethod(Invocation invocation) {
throw new NoSuchMethodError(this, invocation.memberName,
invocation.positionalArguments, invocation.namedArguments);
}
@patch
Type get runtimeType => getRuntimeType(this);
}
打开移动端Object实现文件./vm/lib/object_patch.dart,如下:
// part of "core_patch.dart";
@pragma("vm:exact-result-type", "dart:core#_Smi")
int _getHash(obj) native "Object_getHash";
void _setHash(obj, hash) native "Object_setHash";
@patch
@pragma("vm:entry-point")
class Object {
// The VM has its own implementation of equals.
@patch
@pragma("vm:exact-result-type", bool)
@pragma("vm:prefer-inline")
bool operator ==(Object other) native "Object_equals";
// Helpers used to implement hashCode. If a hashCode is used, we remember it
// in a weak table in the VM (32 bit) or in the header of the object (64
// bit). A new hashCode value is calculated using a random number generator.
static final _hashCodeRnd = new Random();
static int _objectHashCode(obj) {
var result = _getHash(obj);
if (result == 0) {
// We want the hash to be a Smi value greater than 0.
result = _hashCodeRnd.nextInt(0x40000000);
do {
result = _hashCodeRnd.nextInt(0x40000000);
} while (result == 0);
_setHash(obj, result);
}
return result;
}
@patch
int get hashCode => _objectHashCode(this);
int get _identityHashCode => _objectHashCode(this);
@patch
String toString() native "Object_toString";
// A statically dispatched version of Object.toString.
static String _toString(obj) native "Object_toString";
@patch
@pragma("vm:entry-point", "call")
dynamic noSuchMethod(Invocation invocation) {
// TODO(regis): Remove temp constructor identifier 'withInvocation'.
throw new NoSuchMethodError.withInvocation(this, invocation);
}
@patch
@pragma("vm:exact-result-type", "dart:core#_Type")
Type get runtimeType native "Object_runtimeType";
@pragma("vm:entry-point", "call")
@pragma("vm:exact-result-type", bool)
static bool _haveSameRuntimeType(a, b) native "Object_haveSameRuntimeType";
// Call this function instead of inlining instanceof, thus collecting
// type feedback and reducing code size of unoptimized code.
@pragma("vm:entry-point", "call")
bool _instanceOf(instantiatorTypeArguments, functionTypeArguments, type)
native "Object_instanceOf";
// Group of functions for implementing fast simple instance of.
@pragma("vm:entry-point", "call")
bool _simpleInstanceOf(type) native "Object_simpleInstanceOf";
@pragma("vm:entry-point", "call")
bool _simpleInstanceOfTrue(type) => true;
@pragma("vm:entry-point", "call")
bool _simpleInstanceOfFalse(type) => false;
}
可以看到Object里各种external声明方法对应的@patch注解实现方法
网友评论