Running the Run Loop

You have numerous ways in which to run the run loop. Using run, control is passed to the run loop until all input sources in the NSDefaultRunLoopMode mode have been removed; if there are no input sources, the run loop returns immediately:

[[NSRunLoop currentRunLoop] run];

To specify a time at which the run loop should stop processing events and return control, use runUntilDate::

[[NSRunLoop currentRunLoop] runUntilDate:aDate];

To specify a mode other than NSDefaultRunLoopMode, use runMode:beforeDate:. This method runs the run loop only once; it returns either after it processes a single input source or the beforeDate date is reached. To run any mode continuously, invoke runMode:beforeDate: in a loop with a date far in the future:

while ( [[NSRunLoop currentRunLoop] runMode:NSModalPanelRunLoopMode

                beforeDate:[NSDate distantFuture]] );

The return value of runMode:beforeDate: indicates whether the run loop is still running; if the run loop is empty (in other words, it has no input sources) runMode:beforeDate: returns NO and the while loop exits.

Finally, to conditionalize the run loop so that you can define an exit condition, include a test in the loop surrounding the runMode:beforeDate: invocation:

double resolution = 1.0;

BOOL endRunLoop = NO;

BOOL isRunning;

do {

    NSDate* next = [NSDate dateWithTimeIntervalSinceNow:resolution];

    isRunning = [[NSRunLoop currentRunLoop] runMode:NSDefaultRunLoopMode

                beforeDate:next];

} while (isRunning && !endRunLoop);

In this snippet, the endRunLoop variable is the test condition indicating when to break out of the run loop. It may be either a global variable or an instance variable that is set to YES from a run loop callout when it is time to exit the run loop.

Note: Regardless of the date you specify in runMode:beforeDate: and runUntilDate:, a run loop with nothing to do (that is no sources from which to receive input) exits immediately. You must add the input sources to the run loop mode before you start the run loop. Other parts of the system may add their own sources to a particular run loop mode, but do not depend on this always being the case. Add an empty NSPort to a run loop if you need to guarantee that it does not exit immediately

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Last updated: 2005-01-11

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