iPhone開源系列：UIAlertView-Block

      在iPhone項目開發(fā)的過程中，重新造輪子的事情屢見不鮮，一方面源于開發(fā)者的“自我”心態(tài)，但更多的是因為對開發(fā)項目的不了解。希望通過這樣一個系列和大家一起發(fā)現(xiàn)和挖掘項目開發(fā)中常用的開源項目，共同改進iPhone應(yīng)用開發(fā)。

     UIAlertView和UIActionSheet都采用了Delegate模式，在同一個視圖控制器中使用多個UIAlertView或UIActionSheet時控制器需要同時充當(dāng)它們的delegate，這種情況下處理函數(shù)中通常需要通過tag進行區(qū)分后處理。這樣就經(jīng)常會造成如下代碼：

- (void)alertView:(UIAlertView *)alertView didDismissWithButtonIndex:(NSInteger)buttonIndex {
    if ([alertView tag] == LOGIN_ERROR_ALERT) {    // it's alert for login error
        if (buttonIndex == 0) {     // and they clicked OK.
            // do stuff
        }
    }
    else if ([alertView tag] == UPDATE_ERROR_ALERT) {   // it's alert for update error
        if (buttonIndex == 0) {     // and they clicked OK.
            // do stuff
        }   
    }
    else {
    }
}

     這種針對tag的分支判斷就會影響到代碼可讀性，并產(chǎn)生壞味道。UIAlertView-Block（https://github.com/jivadevoe/UIAlertView-Blocks）項目就可以克服這樣的問題。該項目提供了可以使用代碼塊來處理按鈕事件的UIAlertView和UIActionSheet的Category，示例代碼如下：

RIButtonItem *cancelItem = [RIButtonItem item];
cancelItem.label = @"No";
cancelItem.action = ^
{
    // this is the code that will be executed when the user taps "No"
    // this is optional... if you leave the action as nil, it won't do anything
    // but here, I'm showing a block just to show that you can use one if you want to.
};

RIButtonItem *deleteItem = [RIButtonItem item];
deleteItem.label = @"Yes";
deleteItem.action = ^
{
    // this is the code that will be executed when the user taps "Yes"
    // delete the object in question...
    [context deleteObject:theObject];
};

UIAlertView *alertView = [[UIAlertView alloc] initWithTitle:@"Delete This Item?" message:@"Are you sure you want to delete this really important thing?" cancelButtonItem:cancelItem otherButtonItems:deleteItem, nil]; [alertView show]; [alertView release];

   有了這樣一個項目，是不是再次看到根據(jù)tag區(qū)分進行分支處理時會有一種重構(gòu)的沖動呢？