为动态创建的 UIPickerView 添加协议

Question

这个问题与SO question (please see accepted answer)有关。我正在将 UIPickerView 添加到未在其视图中添加 UIPickerViewDelegate 或 UIPickerViewDataSource 协议的视图界面。但是，UIPickerView 对象所需的所有方法都已正确实现，程序在这些委托下运行良好：

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

由于class接口中没有添加协议，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

此代码似乎添加了所需的协议，并且一旦为选取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。

执行或分配是否有误？

更新： 错误截图

Answer 1

您正在尝试将 class 设置为委托人。请设置一个实例来解决此问题。

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;

在定义您的自定义委托协议时仅使用

@property(nonatomic,assign)id delegate;

而不是

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

为动态创建的 UIPickerView 添加协议

Adding protocols for dynamically created UIPickerView

delegates

protocols

objective-c

uipickerview

ios