How do I use IF-loops with plot_handles?

Question

fxo 2013-5-20

0
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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/76439-how-do-i-use-if-loops-with-plot_handles

I'm having a bit of a problem to integrate the if-loop with plot handles. So the program I'm writing has this structure:

It has this menufile in which you choose what you want to do (This is only a small part of it):

    case 1
    plot_handles = createPlot(plot_handles);
    case 2
    changeWidth(plot_handles);

In case 1 you'll be able to index a figure and write the function which is plotted and you're being returned to the menu.

    function plot_handles = createPlot(plot_handles)
    clc
    try 
    figureid = input('Input figure-ID: ');
    func= input('Input function f(x): ','s');
    figure(figureid);
    h=ezplot(func); 
    plot_handles(figureid)=h;
    catch
    lasterr
    error('Nonvalid function!');
    end
    end

Back in the menu I enter case 2 where the thought is that it'll ask you which figure you want to edit.Once you've choosen that you're supposed to be able to edit that figures' linewidth:

    function changeWidth(plot_handles)
    figureid = input('Input figure-ID: ');
    h = plot_handles(figureid);
    if exist(figureid)== 0 % Here's the problem, I don't know how to test if ...
    % the ID is correct or not.
        error('Invalid figure-ID')
    else
    width=input('Input new width: ');
    set(h, 'linewidth', width) 
    end

The problem is that I don't know how to check if figure-ID is correct in the IF-loop, elsewhere I want the errormessage so be written out.

Would really appreciate some help!

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Answer 1

per isakson 2013-5-20

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编辑：per isakson 2013-5-20

在 MATLAB Online 中打开

"check if figure-ID is correct "

There is a function:

    ishandle
    Test for valid graphics object handle

Continue:

I think code cells are useful when experimenting with code, see Evaluate Subsections of Files Using Code Cells. One small step at a time, check the result and proceed to next step.

Doc says:

h = ezplot(...) returns the handle to all the plot objects in h.

My first step:

    h = ezplot( @sin );
    get( h, 'Type' )

returns

    ans =
    line

Thus, ezplot returned the handle of the line object. Did you expect that?

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fxo 2013-5-20

I solved it on my own using ishandle as you said, once again, thank you for the waypointer!

per isakson 2013-5-20

"right way" that depends on who you ask. I doubbt.

I hessitate to use the same variable, h, as handle to a graphic object and index to a double array.
I hessitate to rely on current figure and current axes when more than one figure or axes exist simultaneously.

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