ios - 在循环期间更新 UIProgressBar 进度

Question

我找不到关于如何在迭代循环时更新 UIProgressbar 进度的明确答案，例如：

for (int i=0;i<items.count;i++) {
    Object *new = [Object new];
    new.xxx = @"";
    new...
    ...
    float progress = (i+1) / (float)items.count;
    progressBar.progress = progress;
}
[self save];

如何在单独的线程上更新 UI？

Answer 1

在后台线程上运行循环，并在主线程上更新进度条：

dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_BACKGROUND, 0), ^{
    for (int i=0;i<items.count;i++) {
        Object *new = [Object new];
        new.xxx = @"";
        new...
        ...
        float progress = (i+1) / (float)items.count;
        dispatch_async(dispatch_get_main_queue(), ^{
            progressBar.progress = progress;
        });

    }
    [self save];
});