接续上期文章《Python调用BarTender SDK实现数据源修改与打印操作详解》，许多读者反馈希望了解如何实现对BTW模板的预览功能。本文将深入讲解通过Python调用BarTender SDK生成标签预览图及打印的技术方案。
一、功能执行流程
二、功能架构设计
class BTWPreviewApp:
def __init__(self, root):
# 核心组件
self.engine = None # BarTender引擎实例
self.format_doc = None # 当前打开的标签文档
self.ui_queue = queue.Queue() # 线程安全队列
self.bartender_available = False # BarTender可用标志
# GUI组件
self.file_tree = None # 文件列表树
self.preview_label = None # 预览区域
self.printer_combo = None # 打印机选择
三、核心功能实现
1. BarTender引擎初始化与检查
def check_bartender_availability(self):
"""检查BarTender可用性"""
try:
import clr
dll_path = os.path.join(os.path.dirname(__file__), 'Seagull.BarTender.Print.dll')
if os.path.exists(dll_path):
clr.AddReference(dll_path)
from Seagull.BarTender.Print import Engine
# 测试引擎实例
test_engine = Engine(True)
test_engine.Stop()
self.bartender_available = True
else:
self.bartender_available = False
except Exception as e:
self.bartender_available = False
2. BTW文件加载与预览生成
def load_format_with_bartender(self, file_path):
"""使用BarTender加载格式并生成预览"""
try:
from Seagull.BarTender.Print import LabelFormatThumbnail
from System.Drawing import Color
# 关闭之前的格式
if self.format_doc:
self.format_doc.Close()
# 打开新格式
self.format_doc = self.engine.Documents.Open(file_path)
# 生成预览图片
thumbnail = LabelFormatThumbnail.Create(file_path, Color.White, 1200, 1200)
# 两种预览处理方式
try:
# 方法1: 内存流直接转换
from System.IO import MemoryStream
from System.Drawing.Imaging import ImageFormat
memory_stream = MemoryStream()
thumbnail.Save(memory_stream, ImageFormat.Png)
pil_image = Image.open(io.BytesIO(memory_stream.ToArray()))
except:
# 方法2: 临时文件回退方案
pil_image = self._fallback_preview_with_temp_file(thumbnail)
return pil_image
except Exception as e:
return None
3. 预览图像处理与显示
def update_preview_ui(self, pil_image):
"""更新预览图片UI"""
try:
# 调整图片尺寸
max_display_size = 600
img_width, img_height = pil_image.size
if img_width > max_display_size or img_height > max_display_size:
scale = min(max_display_size/img_width, max_display_size/img_height)
new_size = (int(img_width*scale), int(img_height*scale))
pil_image = pil_image.resize(new_size, Image.Resampling.LANCZOS)
# 显示图片
photo = ImageTk.PhotoImage(pil_image)
self.preview_label.configure(image=photo)
self.preview_label.image = photo
except:
# 显示错误占位符
self.preview_label.configure(image="", text="预览加载失败")
4. 打印机管理
def load_printers_async(self):
"""异步加载打印机列表"""
def load_printers():
from Seagull.BarTender.Print import Printers
printers = Printers()
printer_names = []
for i in range(printers.Count):
printer = printers[i]
printer_names.append(printer.PrinterName)
self.ui_queue.put(("update_printers", [printer_names]))
threading.Thread(target=load_printers, daemon=True).start()5. 打印控制
def print_format(self):
"""打印当前文档"""
def print_async():
try:
# 设置选择的打印机
if self.printer_var.get():
self.format_doc.PrintSetup.PrinterName = self.printer_var.get()
# 执行打印
result = self.format_doc.Print()
if result:
self.ui_queue.put(("update_status", ["打印完成"]))
else:
self.ui_queue.put(("update_status", ["打印失败"]))
except Exception as e:
self.ui_queue.put(("show_error", [str(e)]))
threading.Thread(target=print_async, daemon=True).start()四、关键技术点
1. 多线程处理与UI更新机制
def setup_ui_updater(self):
"""设置UI更新器"""
def update_ui():
try:
while not self.ui_queue.empty():
action, args = self.ui_queue.get_nowait()
if action == "update_preview":
self.update_preview_ui(args[0])
elif action == "update_printers":
self.update_printers_ui(args[0])
# 其他UI更新...
self.root.after(100, update_ui)
self.root.after(100, update_ui)
2. 预览生成失败处理
def _fallback_preview_with_temp_file(self, thumbnail):
"""预览生成的回退方案"""
try:
import tempfile
with tempfile.NamedTemporaryFile(suffix='.png', delete=False) as temp_file:
temp_path = temp_file.name
# 保存到临时文件
from System.Drawing.Imaging import ImageFormat
thumbnail.Save(temp_path, ImageFormat.Png)
# 从文件加载
pil_image = Image.open(temp_path)
# 延迟删除临时文件
def delayed_delete():
try:
time.sleep(1)
os.unlink(temp_path)
except: pass
threading.Thread(target=delayed_delete, daemon=True).start()
return pil_image
except:
return None
3. 资源生命周期管理
def on_closing(self):
"""程序关闭时的资源清理"""
# 关闭当前文档
if self.format_doc:
try:
self.format_doc.Close()
except: pass
# 停止BarTender引擎
if self.engine:
try:
self.engine.Stop()
except: pass
# 清理临时文件
if hasattr(self, '_temp_files_to_cleanup'):
for temp_file in self._temp_files_to_cleanup:
try:
os.unlink(temp_file)
except: pass
self.root.destroy()
五、关键技术点
1. .NET互操作
使用Pythonnet库实现Python与.NET的互操作：
import clr
clr.AddReference('Seagull.BarTender.Print')
from Seagull.BarTender.Print import Engine, Printers, LabelFormatDocument2. 异步处理架构
使用多线程处理耗时操作
通过队列机制实现线程间通信
Tkinter的after方法实现UI定时更新
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