为动态创建的UIPickerView添加协议

Question

这个问题与这个)有关。我正在将一个UIPickerView添加到一个没有在其接口中添加UIPickerViewDelegate或UIPickerViewDataSource协议的视图。但是，UIPickerView对象所需的所有方法都已正确实现，程序在以下委托下运行良好：

pv.delegate = self;
pv.dataSource = self;    

由于没有在类接口中添加协议，Xcode相应地抛出这两个警告：

Assigning to 'id<UIPickerViewDelegate>' from incompatible type
Assigning to 'id<UIPickerViewDataSource>' from incompatible type

这段代码似乎添加了所需的协议，并且一旦为选择器视图委托和数据源属性分配了新创建的delegateClass，警告就会停止。

UIPickerView *pv = [[UIPickerView alloc] initWithFrame:CGRectMake(x, y, width, height)];

Class<UIPickerViewDelegate, UIPickerViewDataSource> delegatedClass = (Class<UIPickerViewDelegate, UIPickerViewDataSource>)[self class];

pv.delegate = delegatedClass;
pv.dataSource = delegatedClass;

但是，即使没有错误，程序也会崩溃。

执行或分配是否错误？

更新:错误的屏幕截图

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Answer 1

您正在尝试将类设置为委托。请设置实例以解决此问题。

UIPickerView *pv = [[UIPickerView alloc] initWithFrame:CGRectMake(x, y, width, height)];
pv.delegate = self;

而不是

UIPickerView *pv = [[UIPickerView alloc] initWithFrame:CGRectMake(x, y, width, height)];

Class<UIPickerViewDelegate, UIPickerViewDataSource> delegatedClass = (Class<UIPickerViewDelegate, UIPickerViewDataSource>)[self class];

pv.delegate = delegatedClass;

在定义自定义委托协议时，只使用

@property(nonatomic,assign)id delegate;

而不是

@property(nonatomic,assign)id<YOUR_PROTOCOL> delegate;