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To subform or the subform control don't have such an option. <br />
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But you can set the anchors of the subform control to Both insteaf of Left/Top, then the control hosting your subform will grow and shrink with the form where it is placed on.<br />
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<a href="https://filedb.experts-exchange.com/incoming/2020/03_w13/1447980/Capture.PNG" target="_blank" title="Capture.PNG (33 KB)"><img alt="Capture.PNG" class="file-block lazyload" style="max-width: 800px;" data-src="https://filedb.experts-exchange.com/incoming/2020/03_w13/800_1447980/Capture.PNG" /></a>
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Capture.PNG

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Use the main forms Form_Resize event, which will fire after it is maximized,<br><br>Then use the<br><br>Insideheight and insidewidth properties of the main form to reset the size of the subform, something like<br><br>Private Sub Form_Resize<br><br>&nbsp; &nbsp; me.subformControlname.width = me.insidewidth - (.25 * 1440)<br>&nbsp; &nbsp; me.subformcontrolname.height = me.insideHeight - (1 * 1440) &nbsp;<br><br>End Sub<br><br>This assumes a form header of .75" and margins around the subform of .125 " on all sides. &nbsp;
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Try this :<br><pre><code class="code-1 nolinks" id="code-20-43054417-1"><span>DoCmd.Maximize ' The Master form maximizing</span>
<span>Me.SubForm.Width = Me.WindowWidth</span>
<span>Me.SubForm.Height = Me.WindowHeight * 0.5 (50% of the master form)</span>
</code></pre>
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John, I'm trying this:<br />
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&nbsp; &nbsp; DoCmd.Maximize ' The Master form maximizing<br />
&nbsp; &nbsp; Me.subfrmProductInventory.<wbr />Width = Me.WindowWidth<br />
&nbsp; &nbsp; Me.subfrmProductInventory.<wbr />Height = Me.WindowHeight * 0.5 '(50% of the master form)<br />
<br />
But when I try to compile I get a message indicating that the subform can't be found.
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Check exactly how your subform is named as a child in your parent form...not the name of the subform.<br>Just go the parent form properties and find subform as a control.
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You need to use the subform control name, which may be different than the name of the form used as the subforms sourceobject.<br><br>Dale
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SteveL13

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Using the anchors for the subform seemed to work best.
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I don't generally use anchors, because I generally have more controls on the form and want explicit control over where they go, anchors don't give me quite that level of control.<br><br>I also like to use the form resize event because I can limit how much the user is allowed to shrink the form, so that it doesn't go below a certain size.<br><br><br>
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I have a form and a subform. &nbsp;I have the form set to maximize onopen. &nbsp;But no matter what I try I can't get the subform to maximize onopen. &nbsp;What am I doing wrong?
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I have a form and a subform.  I have the form set to maximize onopen.  But no matter what I try I can't get the subform to maximize onopen.  What am I doing wrong?

Subform won't maximize onopen.

Microsoft Access is a rapid application development (RAD) relational database tool. Access can be used for both desktop and web-based applications, and uses VBA (Visual Basic for Applications) as its coding language.