Get handle of subplot with CData

The following throws a 'There is no CData property on the Axes class' error, but I don't know how to resolve it.

 % initiate figure and get subplot handles
 ynum      = 100;
 xnum      = 100;
 xgrid     = 0:1:(xnum-1);
 ygrid     = 0:1:(ynum-1);

 figure(2); hold on;
 subplot(2,2,1);  imagesc(xgrid,ygrid,zeros(ynum,xnum));  caxis([0    0.75]);  colormap(jet(256));  colorbar;  title('0');               
 subplot(2,2,2);  imagesc(xgrid,ygrid,zeros(ynum,xnum));  caxis([0    1.00]);  colormap(jet(256));  colorbar;  title('phase field (P1)'); 
 subplot(2,2,3);  imagesc(xgrid,ygrid,zeros(ynum,xnum));  caxis([0.15 0.85]);  colormap(jet(256));  colorbar;  title('comp field (A)');  
 subplot(2,2,4);  imagesc(xgrid,ygrid,zeros(ynum,xnum));  caxis([1    1000]);  colormap(jet(256));  colorbar;  title('crystal field');   

 handles.img(1) = subplot(2,2,1); truesize;
 handles.img(2) = subplot(2,2,2); truesize;
 handles.img(3) = subplot(2,2,3); truesize;
 handles.img(4) = subplot(2,2,4); truesize;

 hold off;

 % update figure
 for t=1:10
     figure(2);
     set(handles.img(1),'CData',rand(ynum,xnum));  title(num2str(t));
     set(handles.img(2),'CData',rand(ynum,xnum));
     set(handles.img(3),'CData',rand(ynum,xnum));
     set(handles.img(4),'CData',rand(ynum,xnum));
 end

Answer 1

[Walter Roberson]

subplot(2,2,2); handles.img(2) = imagesc(xgrid,ygrid,zeros(ynum,xnum)); caxis([0 1.00]); colormap(jet(256)); colorbar; title('phase field (P1)');