Hippy/framework/ios/utils/HippyWeakProxy.m

/*!
 * iOS SDK
 *
 * Tencent is pleased to support the open source community by making
 * Hippy available.
 *
 * Copyright (C) 2019 THL A29 Limited, a Tencent company.
 * All rights reserved.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

#import "HippyWeakProxy.h"

@interface HippyWeakProxy ()

@property (nonatomic, weak) id target;

@end

@implementation HippyWeakProxy

+ (instancetype)weakProxyForObject:(id)target {
    HippyWeakProxy *proxy = [HippyWeakProxy alloc];
    proxy.target = target;
    return proxy;
}

- (id)forwardingTargetForSelector:(SEL)aSelector {
    return _target;
}

- (BOOL)respondsToSelector:(SEL)aSelector {
    return [_target respondsToSelector:aSelector];
}

#pragma mark Handling Unimplemented Methods

- (void)forwardInvocation:(NSInvocation *)invocation {
    // Fallback for when target is nil. Don't do anything, just return 0/NULL/nil.
    // The method signature we've received to get here is just a dummy to keep `doesNotRecognizeSelector:` from firing.
    // We can't really handle struct return types here because we don't know the length.
    void *nullPointer = NULL;
    [invocation setReturnValue:&nullPointer];
}

- (NSMethodSignature *)methodSignatureForSelector:(SEL)selector {
    // We only get here if `forwardingTargetForSelector:` returns nil.
    // In that case, our weak target has been reclaimed. Return a dummy method signature to keep `doesNotRecognizeSelector:` from firing.
    // We'll emulate the Obj-c messaging nil behavior by setting the return value to nil in `forwardInvocation:`, but we'll assume that the return
    // value is `sizeof(void *)`. Other libraries handle this situation by making use of a global method signature cache, but that seems heavier than
    // necessary and has issues as well. See https://www.mikeash.com/pyblog/friday-qa-2010-02-26-futures.html and
    // https://github.com/steipete/PSTDelegateProxy/issues/1 for examples of using a method signature cache.
    return [NSObject instanceMethodSignatureForSelector:@selector(init)];
}

@end