编译F＃报价：性能？(Compiling an F# quotation: performance?)

 有一个UIPickerViewDelegate方法，每次滚动选择器时基本上都会触发该方法 
 
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
 
 设置选择器的委托，实现此方法，看看会发生什么...... 
 
 [编辑]好了，我现在明白了你的需求。 实现一个计时器，检查选择器的状态。 
 
checkTimer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(checkPicker) userInfo:nil repeats:YES];
 
 在上面的委托方法中，存储上次移动选择器的时间。 
 
lastPickerDate = [[NSDate date] retain];
 
 在checkPicker方法中检查从上次移动开始经过的时间 
 
NSTimeInterval timeSinceMove = -[lastPickerDate timeIntervalSinceNow];
 
 如果timeSinceMove大于某个所需的值，即0.5秒，则将BOOL pickerMoving设置为false。 否则将其设置为true。 这不是检查运动的最精确方法，但我认为应该做的工作...... 

There is a UIPickerViewDelegate method which is basically triggered every time you scroll the picker
 
- (NSString *)pickerView:(UIPickerView *)pickerView titleForRow:(NSInteger)row forComponent:(NSInteger)component
 
Set the delegate for your picker, implement this method and see what happens...
 
[EDIT] ok now I understand what you need. Implement a timer which checks the state of the picker. 
 
checkTimer = [NSTimer scheduledTimerWithTimeInterval:0.01 target:self selector:@selector(checkPicker) userInfo:nil repeats:YES];
 
in the above delegate method, store the last time the picker had been moved.
 
lastPickerDate = [[NSDate date] retain];
 
in the checkPicker method check how much time had elapsed from the last move
 
NSTimeInterval timeSinceMove = -[lastPickerDate timeIntervalSinceNow];
 
if timeSinceMove is bigger then some desired value i.e. 0.5 seconds, set your BOOL pickerMoving to false. else set it to true. This is not the most precise method to check for movement, but I think it should do the job...