ios - 自定义UIView并在访问属性时崩溃

Question

所以我有一个子类UIView：

.h
@interface HistogramGraphPanel : UIView

@property (strong, nonatomic) UIView *graphView;

-(id)initWithDataset:(Dataset *)dataset;

@end

.m
-(id)initWithDataset:(Dataset *)dataset {
    self = [super init];
    if (self) {
        self.dataset = dataset;

        self.translatesAutoresizingMaskIntoConstraints = FALSE;

        UIView *contentView = [UIView new];
        contentView.translatesAutoresizingMaskIntoConstraints = FALSE;
        contentView.backgroundColor = [UIColor orangeColor];
        contentView.tag = 6;
        self.contentView = contentView;

        UIView *headerView = [UIView new];
        headerView.translatesAutoresizingMaskIntoConstraints = FALSE;
        headerView.backgroundColor = [UIColor blueColor];
        self.headerView = headerView;

        [headerView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:[headerView(60)]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(headerView)]];

        [contentView addSubview:headerView];

        [contentView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|[headerView]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(headerView)]];
        [contentView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|[headerView]|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(headerView)]];

        UILabel *headerLabel = [UILabel new];
        headerLabel.translatesAutoresizingMaskIntoConstraints = FALSE;
        headerLabel.font = [UIFont fontWithName:HELVETICA_FONT_STYLE_BOLD size:24];
        headerLabel.text = @"Analysis Histogram";
        headerLabel.backgroundColor = [UIColor clearColor];

        [headerView addSubview:headerLabel];

        [headerView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-[headerLabel]-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(headerLabel)]];
        [headerView addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:|-[headerLabel]" options:0 metrics:nil views:NSDictionaryOfVariableBindings(headerLabel)]];

        [self createGraphView];

        self = (HistogramGraphPanel *)contentView;
    }
    return self;
}

创建和使用UIView子类：

HistogramGraphPanel *graphPanel = [[HistogramGraphPanel alloc] initWithDataset:dataset];

[self.view addSubview:graphPanel];

[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"H:[panel]-[graphPanel]-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(graphPanel, panel)]];
[self.view addConstraints:[NSLayoutConstraint constraintsWithVisualFormat:@"V:|-(49)-[graphPanel]-(228)-|" options:0 metrics:nil views:NSDictionaryOfVariableBindings(panel, graphPanel)]];

DLog(@"graphPanel.graphView: %@", graphPanel.graphView);

在我尝试访问graphPanel.graphView之前，效果很好。

2013-04-25 16:44:58.579 [15666:907] -[UIView graphView]: unrecognized selector sent to instance 0x1e0c8320
2013-04-25 16:44:58.580 [15666:907] *** Terminating app due to uncaught exception 'NSInvalidArgumentException', reason: '-[UIView graphView]: unrecognized selector sent to instance 0x1e0c8320'

实例0x1e0c8320是我创建的graphView的contentView。

如果我不尝试访问该属性，它将在崩溃时运行。

有理想吗？

Answer 1

问题出在您的init方法中。

为什么用self = (HistogramGraphPanel *)contentView;进行整个操作？ contentView不是graphView，但是您可以通过强制转换将self设置为它。我认为，如果您仅省去该行，那么您的代码应该可以工作。

通常，将self分配给除[super init]返回的内容之外的任何内容都不是一个好主意，因为您可能会看到编译器在没有该强制类型的情况下向您发出警告/错误。