Do some controle before generating VisualForce PDF page

Question

I designing a VisualForce PDF page and I am using a controller extension. The generation of the page happens by clicking on an action associated to an Object to show it's different fields' values.

I want to know if it's possible to check the value of some fields before rendering the PDF itself using the extension (is there a lifecycle method to override ? ) or by using a custom controller.

I want to show an error window if there is an issue.

Thanks

Answer 1

There are a few options. You can use the constructor:

public CoordonneesBancairesMandantExtension(ApexPages.StandardController controller) {
  // Check data here //
}

Or as an action:

public PageReference validateData() {
   // Check data here //
}

Which is added as a page action:

<apex:page action="{!validateData}" ...

This example includes a redirect to an error page, etc, by returning a PageReference.

You can also conditionally render as PDF, or not, using the renderAs attribute:

<apex:page renderAs="{!renderMode}" ...

Where the Apex has a method or variable for this, such as:

public String getRenderMode() {
  if(validated()) {
    return 'pdf';
  } else {
    return ''; // Default rendering mode, HTML
  }
}