Understanding Flex Print Job from A to Z （彻底了解FlexPrintJob）（精彩转载）

What is FlexPrintJob

In Flex, you usually do printing in your application through FlextPrintJob.

According to Adobe, FlexPrintJob is:

• A class that prints one or more objects
• Automatically splits large objects for printing on multiple pages
• Scales the output to fit the page size

FlexPrintJob vs. Flash PrintJob

FlexPrintJob is a new print class introduced by Adobe for Flex. In Flash, there is a similar one, named PrintJob.

Here is how you call FlexPrintJob in Flex:

flexPrintJob.addObject(myPrintObject,scaleType)
- myPrintObject is the UIComponent you want to print
- scaleType specifies how to scale UIComponent to fit print page
  (e.g. matchWidth, matchHeight, fillPage, showAll)

To compare, here is how you call PrintJob in Flash:

printJob.addPage(Sprite(myPrintObject), rectangle, printJobOptions)
- myPrintObject is the UIComponent you want to print
- rectangle is the print area defined by a rectangle
- printJboOptions specifies print as a BitMap or in Vector format

So, what is the relationship between those two print classes?

FlexPrintJob is actually a wrapper for PrintJob class.

What does a wrapper class mean in this case? It means:

1.  FlexPrintJob eventually calls Flash PrintJob to finish the printing task.

2.  FlexPrintJob enhances the Flash PrintJob and simplifies its usage.

What is new in FlexPrintJob

Adobe claims that FlexPrintJob automatically slices large object for printing on multiple pages and scales the output to fit the page size.

To do so,  FlexPrintJob wraps the old Flash PrintJob in the following 8 steps:

Step 1:  Convert percentage width or height to explicit width or height

Step 2:  Calculate Scale Ratio based on Print Page Size and ScaleType (e.g. matchWidth)

Step 3:  Scale the print object to the required value

Step 4:  Find the number of pages required in vertical and horizontal

Step 5:  Create the print area in a shape of rectangle

Step 6:  Specify Print Options (BitMap or Vector)

Step 7:  Call Flash PrintJob to print each page

Step 8:  Restore from explicit width or height to percentage width or height

What is missing in FlexPrintJob

FlexPrintJob enhances the Flash PrintJob in terms of scaling the output to fit the page size. However, is it good enough to print large object on multiple pages?

Maybe… as long as you don’t mind cutting text in half or printing only 5% content of TextArea or DataGrid.

As a matter of fact, to really support multiple pages printing in Flex, it need to resolve the following 3 issues:

1. How to scale display objects from screen to printer?

2. How to print the full content of Scrollable Components such as TextArea or DataGrid?

3. How to find the right page breaker to avoid cutting objects (e.g. Text or Image) in half?

Through the implementation of FlexPrintJob, it does not provide good answers to issue#2 and issue#3. Therefore, when come to printing multiple pages in Flex, you often need extra helps like PrintDataGrid or FlexReport.

Note:The paper comes from http://flextutorial.org/2009/06/23/understanding-flex-print-job-from-a-to-z/