随时随地使用 NSTask 获取流程输出？

Question

我想得到NSTask 的输出，因为它似乎不等到进程完成。 我找到了this answer，但是应该如何修改它以尽快获取数据？我想我应该以某种方式运行后台线程并一直等待输出。

Answer 1

您可以注册NSFileHandleDataAvailableNotification 通知以阅读 从任务输出异步。示例：

NSTask *task = [[NSTask alloc] init];
[task setLaunchPath:@"/bin/ls"];
[task setCurrentDirectoryPath:@"/"];

NSPipe *stdoutPipe = [NSPipe pipe];
[task setStandardOutput:stdoutPipe];

NSFileHandle *stdoutHandle = [stdoutPipe fileHandleForReading];
[stdoutHandle waitForDataInBackgroundAndNotify];
id observer = [[NSNotificationCenter defaultCenter] addObserverForName:NSFileHandleDataAvailableNotification
                                                                object:stdoutHandle queue:nil
                                                            usingBlock:^(NSNotification *note) 
{
    // This block is called when output from the task is available.

    NSData *dataRead = [stdoutHandle availableData];
    NSString *stringRead = [[NSString alloc] initWithData:dataRead encoding:NSUTF8StringEncoding];
    NSLog(@"output: %@", stringRead);

    [stdoutHandle waitForDataInBackgroundAndNotify];
}];

[task launch];
[task waitUntilExit];
[[NSNotificationCenter defaultCenter] removeObserver:observer];

或者，您可以在后台线程上阅读，例如使用 GCD：

NSTask *task = [[NSTask alloc] init];
[task setLaunchPath:@"/bin/ls"];
[task setCurrentDirectoryPath:@"/"];

NSPipe *stdoutPipe = [NSPipe pipe];
[task setStandardOutput:stdoutPipe];

NSFileHandle *stdoutHandle = [stdoutPipe fileHandleForReading];
dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_LOW, 0), ^{
    NSData *dataRead = [stdoutHandle availableData];
    while ([dataRead length] > 0) {
        NSString *stringRead = [[NSString alloc] initWithData:dataRead encoding:NSUTF8StringEncoding];
        NSLog(@"output: %@", stringRead);
        dataRead = [stdoutHandle availableData];
    }
});

[task launch];
[task waitUntilExit];