如何在不必单击的情况下显示注释上的信息

for (MyAnnotation *a in dealerMapView.annotations) {
    // Your current position (if shown) is an annotation as well. Thus check for the right class!
    if ([a isKindOfClass:[MyAnnotation class]]) {
        // insert some smart if statement here, if you have multiple annotations!
        [[dealerMapView viewForAnnotation:a] setSelected:YES animated:YES];
    }
}

我使用了上面的代码，但信息没有显示在pin上。