为什么这个for循环不执行？

Question

我有一个选择器视图控制器来选择化学源和可能的浓度。如果源没有集中，它只显示一个选择器。它由一个 NSDictionary 填充，其中源类型名称为 keys 以及我制作的名为 Chemical 的自定义模型对象，该对象具有四个属性，两个 >NSString，一个 float 和一个 BOOL。

当我使用具有 2 个组件的字典触发此操作时，我想从所表示的 Chemical 中提取四个值。请注意，我使用前两个属性的值填充选取器，而不是 float 或 BOOL。我遍历第一个组件中选择的键的数组，并根据键中每个 Chemical 的 chemConcentration 属性检查第二个组件中的字符串/值数组。当 chemConcentration 匹配时，我知道我拥有正确的 Chemical 并且我可以获取其属性并发回。

哇！

问题是，尽管我知道我进入了 for 循环，但它似乎被跳过了。 NSLog 就在它打印之前，但里面的却没有打印。 sourceConstant 和 sourceIsLiquid 保持 0.0 和 NO

- (IBAction)selectedSourceButton {
    NSLog(@"selectedSourceButton pressed");
    NSInteger sourceRow = [picker selectedRowInComponent:kSourceComponent];
    NSString *selectedSource = [self.sources objectAtIndex:sourceRow];
    NSArray *selectedChemicalGroup = [dictionaryOfSources objectForKey:selectedSource];
    NSInteger concentrationRow = [picker selectedRowInComponent:kConcentrationComponent];
    NSString *selectedConcentration = [[NSString alloc] init];
    float selectedConstant = 0.0;
    BOOL selectedIsLiquid = NO;

    if (numberOfComponents == 2) {
        NSLog(@"numberOfComponents = 2 if/then chosen"); // <-- This prints.
        selectedConcentration = [self.concentrations objectAtIndex:concentrationRow];
        NSLog(@"begin selectedConcentration for loop.  Number of loops = %d", [selectedChemicalGroup count]); // <-- And so does this.
        for (int i; i<[selectedChemicalGroup count]; i++) { // <-- But this doesn't seem to fire!
            NSLog(@"selectedConcentration = %@, from selectedChemicalGroup = %@", selectedConcentration, [[selectedChemicalGroup objectAtIndex:i] chemConcentration]); // <-- Because this doesn't print.
            if ([selectedConcentration isEqualToString:[[selectedChemicalGroup objectAtIndex:i] chemConcentration]]) {
            selectedConstant = [[selectedChemicalGroup objectAtIndex:i] chemConstant];
            selectedIsLiquid = [[selectedChemicalGroup objectAtIndex:i] chemIsLiquid];
            }
        }
    }
    else {
        selectedConcentration = @"";
        selectedConstant = [[selectedChemicalGroup objectAtIndex:0] chemConstant];
        selectedIsLiquid = [[selectedChemicalGroup objectAtIndex:0] chemIsLiquid];
    }
    NSLog(@"selectedSourceButton source to return = %@, concentration = %@, sourceConstant = %1.7f, isLiquid = %d", selectedSource, selectedConcentration, selectedConstant, selectedIsLiquid);
    if ([self.delegate respondsToSelector:@selector (sourcePickerViewController:didSelectSource:andConcentration:andConstant:andIsLiquid:)]) {
        [self.delegate sourcePickerViewController:self didSelectSource:selectedSource andConcentration:selectedConcentration andConstant:selectedConstant andIsLiquid:selectedIsLiquid];
    }
}

Answer 1

您需要初始化变量 i： for (int i = 0; ...

但有更好的方法来做到这一点，使用“快速枚举”：

for (MyChemicalGroupClass *group in selectedChemicalGroup) {
    if ([selectedConcentration isEqualToString:[group chemConcentration]]) {
    ...
    }
}

Answer 2

初始化循环计数 i

for (int i = 0; i<[selectedChemicalGroup count]; i++)

Answer 3

执行以下操作，您就会明白原因：

int i;
NSLog(@"%d", i);