isvalid (Data Acquisition Toolbox)

Data Acquisition Toolbox

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isvalid

Examples See Also

Check for valid device objects, channels, or lines.

Syntax

isvalid(obj)

isvalid(obj.Channel(index))

isvalid(obj.Line(index))

Description

isvalid(obj) returns a "1" if obj is a valid device object and a "0" if obj is not a valid device object. An invalid object exists in the workspace but does not exist in the engine. Therefore, invalid objects are no longer associated with any hardware and should be cleared from the workspace.

isvalid(obj.Channel(index)) returns a logical array containing a "1" where the channels associated with obj are valid, and a "0" where they are not. Invalid channels are no longer associated with any hardware and should be cleared from the workspace.

isvalid(obj.Line(index)) returns a logical array containing a "1" where the lines associated with obj are valid, and a "0" where they are not. Invalid lines are no longer associated with any hardware and should be cleared from the workspace.

Note:
Typically, you use isvalid directly only when you are creating your own M-files.

Examples

Suppose you create the analog input object ai for a National Instruments board and add 8 channels to it.

ai = analoginput('nidaq', 1);
ch = addchannel(ai, 0:7);

To verify the device object is valid

isvalid(ai)
ans =
     1

To verify the channels are valid

isvalid(ch)
ans =
     1     1     1     1     1     1     1     1

If you delete a channel, then isvalid returns a logical "0" in the appropriate location

delete(ai.Channel(3))
isvalid(ch)
ans =
     1     1     0     1     1     1     1     1

Typically, you will use isvalid directly only when you are creating your own M-files. Suppose you create the function func for use with the Data Acquisition Toolbox. If func is passed the previously defined device object ai as an input argument

func(ai);

the first thing you should do in the function is check if ai is a valid device object.

function func(obj)
% Determine if an invalid handle was passed.
if ~isvalid(obj)
   error('Invalid Data Acquisition object passed.');
end

You can examine the Data Acquisition Toolbox M-files for examples using isvalid.