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POComponent Writing - How to correctly handle misentered Object Inspector values?
 

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  1. POComponent Writing - How to correctly handle misentered Object Inspector values?
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    <p>Quick question I cannot find any information on.</p> <p>On one of my components I am creating I have a value which is of Integer type.</p> <p>I need to allow only values entered in the Object Inspector to be between 0-10, anything that falls outside of this range should display a message to say that the value inputted is not appropriate, and then return the focus back to the Delphi Object Inspector.</p> <p>Example:</p> <pre><code>TMyComponent = class(TComponent) private FRangeVal: Integer; procedure SetRangeVal(const Value: Integer); public constructor Create(AOwner: TComponent); override; destructor Destroy; override; published property RangeVal: Integer read FRangeVal write SetRangeVal default 0; end; ... procedure SetRangeVal(const Value: Integer); var OldValue: Integer; begin OldValue := Value; if (Value &lt; 0) or (Value &gt; 10) then begin MessageDlg('Please enter a value between 0-10', mtError, [mbOK], 0); // FRangeVal := OldValue; ?? revert to the last value that worked // return focus back to property in Inspector ?? end else begin if Value &lt;&gt; FRangeVal then begin FRangeVal := Value; end; end; end; </code></pre> <p>Do I need to raise some kind of special built in exception that I am unaware of maybe? The above works with my message box popping up, but focus to the culprit property in the Object Inspector is lost and I have to re click back into it to change the value again. If the entered value is bad I just want to show the message and return the focus so I can quickly enter a new value.</p> <p>PS, code above was written in the web browser hence the original question showed I did not use the setter SetRangeVal for the property RangeVal - this was just a typing mistake.</p>
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    1. COI'm not in a place to try it with a component, but what happens if you define FRangeVal as an enumerated type? e.g. LimitedNum = 0..10;
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      1. POComponent Writing - How to correctly handle misentered Object Inspector values?
      1. USGlenn1234
    2. COYou don't need `OldValue`. The **old value** is stored in `FRangeVal` and the **new value** is stored/passed in `Value` and only if you are satisfied you store `Value` in `FRangeVal`. Thats the initial use case of a Setter
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      1. POComponent Writing - How to correctly handle misentered Object Inspector values?
      1. USSir Rufo
    3. COI see a procedure `SetRangeVal` but it is never used by the property. `property RangeVal: Integer read FRangeVal write SetRangeVal default 0;` and also, the default of `0` will not change the value to a default of 0, but only show this property as **bold** if it's anything other than `0` in the object inspector.
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      1. USJerry Dodge
 

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