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如何找到flutter external声明方法的实现

如何找到flutter external声明方法的实现

作者: HawkFlying | 来源:发表于2020-12-29 11:42 被阅读0次
    • 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

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