英文:
(Kind of solved but still appreciate better answers) Android Studio: How to identify certain special pages in a PDF file?
问题
我正在编写一个为学校学生生成数学练习册的应用程序。例如，它将生成2到5页的简单数学问题和1到2页的答案。PDF可以保存到文件并在以后加载。然后它有一个可以打印所有页面的打印功能。我想让它跳过打印答案页。
是否有可能自动识别哪些页面是答案页？我只能想到一种解决方法，即使那些答案页面具有特殊的高度或宽度，但甚至不确定是否有效。是否有更好的方法来做到这一点？
英文:
I am writing an app that generates Maths worksheets for school students. It will, for example, generate 2 to 5 pages of simple Maths questions and 1 to 2 pages of answers. The PDF can be saved to file and loaded again later. Then it has a print function that can print all the pages. I want to make it skip printing the answer pages.
Is it possible to automatically identify which pages are the answer pages? I can only think of a workaround by making those answer pages have special height or width but not even sure if this works. Are there any better ways to do this?
答案1
得分: 0
好的，以下是您要翻译的内容：
在继续项目时，我使用了以下方法：在构建PDF时，我将单词“Answer”放在左上角，并用drawRect()绘制灰色矩形围绕它。然后，在实际打印之前，我在PrintDocumentAdapter()类中使用以下代码来检查像素0,0的颜色是否为灰色。
@Override
public void onStart() {
if (parcelFileDescriptor != null) {
try {
pdfRenderer = new PdfRenderer(parcelFileDescriptor);
} catch (IOException e) {
e.printStackTrace();
}
}
int tempTotal = pdfRenderer.getPageCount();
Bitmap[] tempBitmap = new Bitmap[tempTotal];
finalTotal = tempTotal;
for (int pageNum = 0; pageNum < tempTotal; pageNum++) {
PdfRenderer.Page tempPage = pdfRenderer.openPage(pageNum);
tempBitmap[pageNum] = Bitmap.createBitmap(WS_WIDTH, WS_HEIGHT, Bitmap.Config.ARGB_8888);
tempPage.render(tempBitmap[pageNum], null, null, PdfRenderer.Page.RENDER_MODE_FOR_PRINT);
if (tempBitmap[pageNum].getPixel(0, 0) == Color.GRAY) {
finalTotal--;
}
tempPage.close();
}
}
它运行正常。至少，如果用户只尝试打印使用我的应用构建的PDF文件，不应该出现问题。 
如果您知道更好的方法，请告诉我。谢谢！
英文:
Ok, I continued the project and used the following method: when constructing the PDF, I put the word "Answer on the top left corner with a gray rectangle surrounding it drawn with drawRect(). Then before the actual printing, I used the following code inside the PrintDocumentAdapter() class to check whether the color of the pixel 0,0 is gray or not.
@Override
public void onStart() {
if (parcelFileDescriptor != null) {
try {
pdfRenderer = new PdfRenderer(parcelFileDescriptor);
} catch (IOException e) {
e.printStackTrace();
}
}
int tempTotal = pdfRenderer.getPageCount();
Bitmap[] tempBitmap = new Bitmap[tempTotal];
finalTotal = tempTotal;
for (int pageNum = 0; pageNum < tempTotal; pageNum++) {
PdfRenderer.Page tempPage = pdfRenderer.openPage(pageNum);
tempBitmap[pageNum] = Bitmap.createBitmap(WS_WIDTH, WS_HEIGHT, Bitmap.Config.ARGB_8888);
tempPage.render(tempBitmap[pageNum], null, null, PdfRenderer.Page.RENDER_MODE_FOR_PRINT);
if (tempBitmap[pageNum].getPixel(0, 0) == Color.GRAY) {
finalTotal--;
}
tempPage.close();
}
}
It works fine. At least should cause no problem if the users only attempt to print PDF files constructed with my app.
Please tell me if you know a better way to do this. Thanks!
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