PdfDocument生成PDF，老是產生空文件

利用PdfDocument生成PDF文件，當內容有變化時，就會產生空文件，不管是page.getCanvas().drawText("12345", 20, 50, paint);

仍是

view1.draw(canvas);

代碼以下：
public void actionGenPdf(View view)
{
    // 建立一個PDF文本對象
    PdfDocument document=new   PdfDocument();
    //建立當前頁的信息，Builder中的參數表示頁面的寬高，以及第幾頁

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

    // 生成當前頁
    PdfDocument.Page page=document.startPage(pageInfo);

    // 在當前頁上畫畫，即把所須要的view的視圖畫到page的畫布上
    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);

    // 輸出到文件
    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, "導出完成", Toast.LENGTH_SHORT).show();
        SoundUtils.getInstance().playSuccess();
    } catch (IOException e) {
        e.printStackTrace();
        Toast.makeText(this, e.getMessage(), Toast.LENGTH_LONG).show();
    }

}