等待[NSAlert beginSheetModalForWindow:...];

当我显示这样的NSAlert时,我立刻得到了回复:

int response;
NSAlert *alert = [NSAlert alertWithMessageText:... ...];
response = [alert runModal];

问题是这是应用程序模式,我的应用程序是基于文档的.我使用工作表在当前文档的窗口中显示警报,如下所示:

int response;
NSAlert *alert = [NSAlert alertWithMessageText:... ...];
[alert beginSheetModalForWindow:aWindow
                  modalDelegate:self
                 didEndSelector:@selector(alertDidEnd:returnCode:contextInfo:)
                    contextInfo:&response];

//elsewhere
- (void) alertDidEnd:(NSAlert *) alert returnCode:(int) returnCode contextInfo:(int *) contextInfo
{
    *contextInfo = returnCode;
}

唯一的问题是beginSheetModalForWindow:直接返回,所以我无法可靠地询问用户问题并等待回复.如果我可以将任务分成两个区域,那么这不会是一件大事,但我不能.

我有一个循环来处理大约40个不同的对象(在树中).如果一个对象出现故障,我希望警报显示并询问用户是继续还是中止(继续在当前分支处理),但由于我的应用程序是基于文档的,因此Apple人机界面指南要求在警报为时使用工作表特定于文件.

如何显示警报表并等待响应？

我们创建了一个类别NSAlert来同步运行警报,就像应用程序模式对话框一样:

NSInteger result;

// Run the alert as a sheet on the main window
result = [alert runModalSheet];

// Run the alert as a sheet on some other window
result = [alert runModalSheetForWindow:window];

代码可以通过GitHub获得,并且下面发布了当前版本的完整性.

头文件NSAlert+SynchronousSheet.h:

#import 


@interface NSAlert (SynchronousSheet)

-(NSInteger) runModalSheetForWindow:(NSWindow *)aWindow;
-(NSInteger) runModalSheet;

@end

实施文件NSAlert+SynchronousSheet.m:

#import "NSAlert+SynchronousSheet.h"


// Private methods -- use prefixes to avoid collisions with Apple's methods
@interface NSAlert ()
-(IBAction) BE_stopSynchronousSheet:(id)sender;   // hide sheet & stop modal
-(void) BE_beginSheetModalForWindow:(NSWindow *)aWindow;
@end


@implementation NSAlert (SynchronousSheet)

-(NSInteger) runModalSheetForWindow:(NSWindow *)aWindow {
    // Set ourselves as the target for button clicks
    for (NSButton *button in [self buttons]) {
        [button setTarget:self];
        [button setAction:@selector(BE_stopSynchronousSheet:)];
    }

    // Bring up the sheet and wait until stopSynchronousSheet is triggered by a button click
    [self performSelectorOnMainThread:@selector(BE_beginSheetModalForWindow:) withObject:aWindow waitUntilDone:YES];
    NSInteger modalCode = [NSApp runModalForWindow:[self window]];

    // This is called only after stopSynchronousSheet is called (that is,
    // one of the buttons is clicked)
    [NSApp performSelectorOnMainThread:@selector(endSheet:) withObject:[self window] waitUntilDone:YES];

    // Remove the sheet from the screen
    [[self window] performSelectorOnMainThread:@selector(orderOut:) withObject:self waitUntilDone:YES];

    return modalCode;
}

-(NSInteger) runModalSheet {
    return [self runModalSheetForWindow:[NSApp mainWindow]];
}


#pragma mark Private methods

-(IBAction) BE_stopSynchronousSheet:(id)sender {
    // See which of the buttons was clicked
    NSUInteger clickedButtonIndex = [[self buttons] indexOfObject:sender];

    // Be consistent with Apple's documentation (see NSAlert's addButtonWithTitle) so that
    // the fourth button is numbered NSAlertThirdButtonReturn + 1, and so on
    NSInteger modalCode = 0;
    if (clickedButtonIndex == NSAlertFirstButtonReturn)
        modalCode = NSAlertFirstButtonReturn;
    else if (clickedButtonIndex == NSAlertSecondButtonReturn)
        modalCode = NSAlertSecondButtonReturn;
    else if (clickedButtonIndex == NSAlertThirdButtonReturn)
        modalCode = NSAlertThirdButtonReturn;
    else
        modalCode = NSAlertThirdButtonReturn + (clickedButtonIndex - 2);

    [NSApp stopModalWithCode:modalCode];
}

-(void) BE_beginSheetModalForWindow:(NSWindow *)aWindow {
    [self beginSheetModalForWindow:aWindow modalDelegate:nil didEndSelector:nil contextInfo:nil];
}

@end

解决方案是打电话

[NSApp runModalForWindow:alert];

在beginSheetModalForWindow之后.此外,您需要实现捕获"对话框已关闭"操作的委托,并调用[NSApp stopModal]作为响应.

这里是解决这一问题的NSAlert类别(如通过与菲利普·弗雷德里克提出,由洛朗P改善:我用一个代码块,而不是委托的解决方案建议,因此它再次简化).

@implementation NSAlert (Cat)

-(NSInteger) runModalSheetForWindow:(NSWindow *)aWindow
{
    [self beginSheetModalForWindow:aWindow completionHandler:^(NSModalResponse returnCode)
        { [NSApp stopModalWithCode:returnCode]; } ];
    NSInteger modalCode = [NSApp runModalForWindow:[self window]];
    return modalCode;
}

-(NSInteger) runModalSheet {
    return [self runModalSheetForWindow:[NSApp mainWindow]];
}

@end

万一有人来找这个(我做了),我解决了以下问题:

@interface AlertSync: NSObject {
    NSInteger returnCode;
}

- (id) initWithAlert: (NSAlert*) alert asSheetForWindow: (NSWindow*) window;
- (NSInteger) run;

@end

@implementation AlertSync
- (id) initWithAlert: (NSAlert*) alert asSheetForWindow: (NSWindow*) window {
    self = [super init];

    [alert beginSheetModalForWindow: window
           modalDelegate: self didEndSelector: @selector(alertDidEnd:returnCode:) contextInfo: NULL];

    return self;
}

- (NSInteger) run {
    [[NSApplication sharedApplication] run];
    return returnCode;
}

- (void) alertDidEnd: (NSAlert*) alert returnCode: (NSInteger) aReturnCode {
    returnCode = aReturnCode;
    [[NSApplication sharedApplication] stopModal];
}
@end

然后同步运行NSAlert就像:

AlertSync* sync = [[AlertSync alloc] initWithAlert: alert asSheetForWindow: window];
int returnCode = [sync run];
[sync release];

请注意,如所讨论的那样存在重新引发问题的可能性,因此如果这样做,请小心.