respondsToSelector总是失败
问题描述:
我正在编写我自己的gridview实现过程(基于tableview模式)。我遵循类似于表视图的数据源模型,但是当我检查数据源是否响应消息时,调用总是失败。respondsToSelector总是失败
我已经试过把断点放在下面执行,我甚至试着错过了对respondsToSelector的调用。没有我尝试似乎工作。我在这里错过了什么?在此先感谢
GridView.h
...
@protocol GridViewDataSource
- (NSInteger) numberOfRowsForGridView:(GridView *)gridView;
- (NSInteger) numberOfColumnsForGridView:(GridView *)gridView;
- (GridViewCell *) cellForRow:(NSInteger) row column:(NSInteger)column;
@end
GridView.m
...
#pragma mark datasource methods
-(NSInteger)numberOfRowsForGridView
{
if([dataSource respondsToSelector:@selector(numberOfRowsForGridView:)])
return [dataSource numberOfRowsForGridView:self];
// NSLog(@"Failed, dataSource does not implement properly");
return 0;
}
-(NSInteger)numberOfColumnsForGridView
{
if([dataSource respondsToSelector:@selector(numberOfColumnsForGridView:)])
return [dataSource numberOfColumnsForGridView:self];
return 0;
}
-(GridViewCell *)cellForRow:(NSInteger)row column:(NSInteger)column
{
if([dataSource respondsToSelector:@selector(cellForRow:column:)])
return [dataSource cellForRow:row column:column];
return nil;
}
GridViewAppDelegate.h
...
@interface GridViewAppDelegate : NSObject <UIApplicationDelegate, GridViewDataSource>
...
GridViewAppDelegate.m
#pragma mark datasource methods
-(NSInteger)numberOfRowsForGridView:(GridView *)gridView
{
return 1;
}
-(NSInteger)numberOfColumnsForGridView:(GridView *)gridView
{
return 1;
}
-(GridViewCell *)cellForRow:(NSInteger)row column:(NSInteger)column
{
CGRect frame = [view bounds];
GridViewCell *cell = [[GridViewCell alloc]initWithFrame:frame];
return cell;
}
答
是您dataSource
对象nil
?
发送到nil
将返回NO
布尔结果任何消息(0数字,和nil
的对象以及)。
答
你检查了dataSource
是否为非零?
Arg,我不敢相信我自己。我只是在init函数中加载视图的数据,而不是在数据源被重置时。非常感谢。 – botptr