NSPredicate 而不是循环来过滤对象数组 [英] NSPredicate instead of loop to filter an array of objects

问题描述

有人告诉我我可以使用 NSPredicate 来复制这个方法的结果

I have been told that I can use NSPredicate to duplicate the results of this method

- (void) clearArrayOut
{
    bool goAgain = false;

    for (int j=0; j<[array count]; j++)
    {
        if ([[array objectAtIndex:j] someMethod] == NO)
        {
            [array removeObjectAtIndex:j];
            goAgain = true;
            break;
        }
    }

    if (goAgain) [self clearArrayOut];
}

如何制作一个 NSPredicate 来根据自定义类调用的某些方法的结果过滤数组?

How can I make an NSPredicate that will filter an array based on the results of some method of a custom class's call?

推荐答案

要制作应用过滤器的副本:

To make a copy with the filter applied:

NSArray *filteredArray = [someArray filteredArrayUsingPredicate:
    [NSPredicate predicateWithBlock:^(id object, NSDictionary *bindings) {
        return [object someMethod]; // if someMethod returns YES, the object is kept
    }]];

要过滤 NSMutableArray 就地:

[someMutableArray filterUsingPredicate:
    [NSPredicate predicateWithBlock:^(id object, NSDictionary *bindings) {
        return [object someMethod]; // if someMethod returns YES, the object is kept
    }]];

但如果我要过滤一个小数组，我可能只会使用 for 循环.但是，我会以稍微不同的方式编写我的 for 循环，以避免减少索引变量或递归调用自己:

But I would probably just use a for loop if I were filtering a small array. However, I'd write my for loop a little differently to avoid having to either decrement the index variable or call myself recursively:

- (void)clearArrayOut:(NSMutableArray *)array {
    for (int i = array.count - 1; i >= 0; --i) {
        if (![[array objectAtIndex:i] someMethod]) {
            [array removeObjectAtIndex:i];
        }
    }
}

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