无法混合类方法

Question

我正在为 Mail.app 制作一个插件。我希望该插件在邮件的工具栏上添加一个按钮。为此，我决定最好的方法是调用函数在 MessageViewer 的初始化方法中添加此按钮（MessageViewer 是 Mail.app 的 FirstResponder 的类）。我正在修改的代码似乎工作得很好：

+ (void) initialize
{  
[super initialize];

//  class_setSuperclass([self class], NSClassFromString(@"MVMailBundle"));
//  [ArchiveMailBundle registerBundle];


// Add a couple methods to the MessageViewer class.
Class MessageViewer = NSClassFromString(@"MessageViewer");

// swizzleSuccess should be NO if any of the following three calls fail
BOOL swizzleSuccess = YES;
swizzleSuccess &= [[self class] copyMethod:@selector(_specialValidateMenuItem:) 
                                 fromClass:[self class] 
                                   toClass:MessageViewer];
swizzleSuccess &= [[self class] copyMethod:@selector(unsubscribeSelectedMessages:) 
                                 fromClass:[self class] 
                                   toClass:MessageViewer];

但是，当我尝试做同样的事情时，它不起作用：

//  //Copy the method to the original MessageViewer
swizzleSuccess &= [[self class] copyMethod:@selector(_specialInitMessageViewer:)
                                 fromClass:[self class]
                                   toClass:MessageViewer];  

以下是混合方法：

+ (BOOL)swizzleMethod:(SEL)origSel withMethod:(SEL)altSel inClass:(Class)cls
{
// For class (cls), swizzle the original selector with the new selector.
    //debug lines to try to figure out why swizzling is failing.
//  if (!cls  ||  !origSel) {
    //          NSLog(@"Something was null.  Uh oh.");
    //}
Method origMethod = class_getInstanceMethod(cls, origSel);

if (!origMethod) {
    NSLog(@"Swizzler -- original method %@ not found for class %@", NSStringFromSelector(origSel), 
          [cls className]);
    return NO;
}
    //if (!altSel) NSLog(@"altSel null.  :(");
Method altMethod = class_getInstanceMethod(cls, altSel);
if (!altMethod) {
    NSLog(@"Swizzler -- alternate method %@ not found for class %@", NSStringFromSelector(altSel), 
          [cls className]);
    return NO;
}

method_exchangeImplementations(origMethod, altMethod);

return YES;

}


+ (BOOL) copyMethod:(SEL)sel fromClass:(Class)fromCls toClass:(Class)toCls
{
    // copy a method from one class to another.
    Method method = class_getInstanceMethod(fromCls, sel);
    if (!method)
    {
        NSLog(@"copyMethod-- method %@ could not be found in class %@", NSStringFromSelector(sel),
              [fromCls className]);
        return NO;
    }
    class_addMethod(toCls, sel, 
                    class_getMethodImplementation(fromCls, sel), 
                    method_getTypeEncoding(method));
    return YES;
}

它似乎在调用 class_getInstanceMethod 时失败，因为我在日志。我自己的类内部的方法以及 MessageViewer 的初始化方法都会发生这种情况。

是否有一些我没有考虑到的问题？

Answer 1

您应该使用 JRSwizzle，而不是尝试手动实现 swizzling。需要注意的是，JRSwizzle 的 +jr_swizzleClassMethod:withClassMethod:error: 实现只是一个存根，但您可以简单地在类的元类上调用 +jr_swizzleMethod:withMethod:error （例如，只需传递 klass->isa 而不是 klass （其中 klass 是您要调配的类））。

Answer 2

如果您想混合类方法，那么为什么要使用 class_getInstanceMethod() 函数而不是 class_getClassMethod() 呢？