PdfDocument生成PDF，总是产生空文件

利用PdfDocument生成PDF文件，当内容有变化时，就会产生空文件，无论是page.getCanvas().drawText("12345", 20, 50, paint);

还是

view1.draw(canvas);

代码如下：
public void actionGenPdf(View view)
{
    // 创建一个PDF文本对象
    PdfDocument document=new   PdfDocument();
    //创建当前页的信息，Builder中的参数表示页面的宽高，以及第几页

    PdfDocument.PageInfo pageInfo=new PdfDocument.PageInfo.Builder(595, 843,1).create();

    // 生成当前页
    PdfDocument.Page page=document.startPage(pageInfo);

    // 在当前页上画画，即把所需要的view的视图画到page的画布上
    Paint paint = new Paint();
    paint.setColor(Color.BLACK);
    paint.setTextSize(20);
    Canvas canvas = page.getCanvas();

    /*for(int i = 0; i < 10; i++) {
        String sTmp = "12345";
        page.getCanvas().drawText("12345", 20, 50, paint);
        canvas.translate(0, 30);
    }*/
    TextView view1 = new TextView(this);//getContentView();
    view1.layout(0, 0, 200, 200);
    view1.setText("Hello");
    TextView view2 = new TextView(this);//getContentView();
    view2.layout(0, 0, 200, 200);
    String sTmp = "Good"+Integer.toString(10);
    final String ss = sTmp;
    view2.setText(ss);
    view1.draw(canvas);
    canvas.translate(0, 200);
    view2.draw(canvas);
    canvas.save();

    /*for(int i = 0; i < 10; i++) {
        TextView view1 = new TextView(this);//getContentView();
        view1.layout(0, 0, 200, 200);
        view1.setText("Hello"+Integer.toString(i));
        Toast.makeText(this,"Hello"+Integer.toString(i), Toast.LENGTH_SHORT).show();
        view1.draw(canvas);
        // Move the canvas for the next view.
        canvas.save();
        canvas.translate(0, 50);
    }*/
    document.finishPage(page);

    // 输出到文件
    try {
        String filePath = "/sdcard/";
        //String filePath = Environment.getExternalStoragePublicDirectory("").getAbsolutePath();
        //String filePath = Environment.getExternalStorageDirectory().getAbsolutePath();
        String fileName = "easy.pdf";
        File file = new File(filePath, fileName);
        FileOutputStream outputStream = new FileOutputStream(file);
        document.writeTo(outputStream);
        PubUtils.notifySystemToScan(this, filePath + fileName);
        Toast.makeText(this, "导出完成", Toast.LENGTH_SHORT).show();
        SoundUtils.getInstance().playSuccess();
    } catch (IOException e) {
        e.printStackTrace();
        Toast.makeText(this, e.getMessage(), Toast.LENGTH_LONG).show();
    }

}