performLayout method
布局
Implementation
@override
performLayout(PrinterConstraints constraints, PrinterCanvas canvas) {
var value = this.dataSource!.execExpressionToValue(condition!);
actualOffset = PrinterOffset.zero;
if (value == true) {
child!.performLayout(constraints, canvas);
actualSize = PrinterSize(child!.actualSize!.width! + child!.actualOffset!.x!, child!.actualSize!.height! + child!.actualOffset!.y!);
} else {
actualSize = PrinterSize.zero;
}
}