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问题解决
首先我查找了查找删除按钮的相关代码,确定了要改动的代码文件,包括布局文件(res/layout/activity_main.xml 以及 activity_preview.xml)和对应的每个界面的Activity文件(java/swati4star/createpdf/activity)。然后,在布局文件中找到删除按钮:在activity_main.xml和activity_preview.xml中,找到定义删除按钮的代码,并为按钮添加一个唯一的id。接着我在各个界面的Activity文件中,修改删除按钮的点击事件,找到设置删除按钮点击事件的原代码,在点击删除按钮之前,添加一个检查条件,确认是否有PDF已经创建。如果没有PDF存在,则禁用按钮或弹出提示。接下来,我实现checkIfPdfCreated(),即检查是否有PDF已经被创建(数据库查询操作)。最后一次迭代是改进了对应UI,在创建和删除PDF的地方调用 deleteButton.setEnabled( true or false),确保UI在状态改变时刷新,如果删除按钮的状态依赖于PDF的创建状态,那么在创建或删除PDF后,确保按钮状态能够动态更新。