如何在Android App中生成PDF文件？

在许多应用程序中，应用程序中的数据以可下载的PDF文件格式提供给用户。因此，在这种情况下，我们必须根据应用程序内部存在的数据创建一个PDF文件，并在我们的应用程序内部正确地表示该数据。因此，通过使用这种技术，我们可以根据需要轻松创建新的PDF。在本文中，我们将研究根据Android应用程序内部的数据创建一个新的PDF文件，并将该PDF文件保存在用户设备的外部存储中。因此，为了从Android应用程序内部的数据生成一个新的PDF文件，我们将使用Canvas。 Canvas是Android中的预定义类，用于在屏幕上绘制不同对象的2D绘图。因此，在本文中，我们将使用画布在画布内绘制数据，然后以PDF的形式存储该画布。现在，我们将继续执行我们的项目。

生成PDF文件的示例

下面是示例GIF，我们将在其中了解我们将要构建的内容。请注意，此应用程序是使用Java语言构建的。在这个项目中，我们将显示一个简单的按钮。单击按钮后，将生成我们的PDF文件，我们可以看到此PDF文件保存在我们的文件中。

分步实施

步骤1：创建一个新项目

要在Android Studio中创建新项目，请参阅如何在Android Studio中创建/启动新项目。请注意，选择Java作为编程语言。

步骤2：使用activity_main.xml文件

转到activity_main.xml文件，并参考以下代码。以下是activity_main.xml文件的代码。

步骤3：在外部存储设备中添加读写权限

导航至应用程序> AndroifManifest.xml文件，然后向其添加以下权限。

步骤4：使用MainActivity。 Java文件

转到MainActivity。 Java文件并参考以下代码。下面是MainActivity的代码。 Java文件。在代码内部添加了注释，以更详细地了解代码。

Java

import android.content.pm.PackageManager;
import android.graphics.Bitmap;
import android.graphics.BitmapFactory;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.Typeface;
import android.graphics.pdf.PdfDocument;
import android.os.Bundle;
import android.os.Environment;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
  
import androidx.annotation.NonNull;
import androidx.appcompat.app.AppCompatActivity;
import androidx.core.app.ActivityCompat;
import androidx.core.content.ContextCompat;
  
import java.io.File;
import java.io.FileOutputStream;
import java.io.IOException;
  
import static android.Manifest.permission.READ_EXTERNAL_STORAGE;
import static android.Manifest.permission.WRITE_EXTERNAL_STORAGE;
  
public class MainActivity extends AppCompatActivity {
  
    // variables for our buttons.
    Button generatePDFbtn;
      
    // declaring width and height 
    // for our PDF file.
    int pageHeight = 1120;
    int pagewidth = 792;
      
    // creating a bitmap variable 
    // for storing our images
    Bitmap bmp, scaledbmp;
      
    // constant code for runtime permissions
    private static final int PERMISSION_REQUEST_CODE = 200;
      
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
          
        // initializing our variables.
        generatePDFbtn = findViewById(R.id.idBtnGeneratePDF);
        bmp = BitmapFactory.decodeResource(getResources(), R.drawable.gfgimage);
        scaledbmp = Bitmap.createScaledBitmap(bmp, 140, 140, false);
  
        // below code is used for 
          // checking our permissions.
        if (checkPermission()) {
            Toast.makeText(this, "Permission Granted", Toast.LENGTH_SHORT).show();
        } else {
            requestPermission();
        }
  
        generatePDFbtn.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                // calling method to 
                  // generate our PDF file.
                generatePDF();
            }
        });
    }
  
    private void generatePDF() {
        // creating an object variable
        // for our PDF document.
        PdfDocument pdfDocument = new PdfDocument();
          
        // two variables for paint "paint" is used
        // for drawing shapes and we will use "title" 
        // for adding text in our PDF file.
        Paint paint = new Paint();
        Paint title = new Paint();
          
        // we are adding page info to our PDF file
        // in which we will be passing our pageWidth,
        // pageHeight and number of pages and after that
        // we are calling it to create our PDF.
        PdfDocument.PageInfo mypageInfo = new PdfDocument.PageInfo.Builder(pagewidth, pageHeight, 1).create();
          
        // below line is used for setting 
        // start page for our PDF file.
        PdfDocument.Page myPage = pdfDocument.startPage(mypageInfo);
          
        // creating a variable for canvas
        // from our page of PDF.
        Canvas canvas = myPage.getCanvas();
          
        // below line is used to draw our image on our PDF file.
        // the first parameter of our drawbitmap method is
        // our bitmap
        // second parameter is position from left
        // third parameter is position from top and last
        // one is our variable for paint.
        canvas.drawBitmap(scaledbmp, 56, 40, paint);
  
        // below line is used for adding typeface for 
        // our text which we will be adding in our PDF file.
        title.setTypeface(Typeface.create(Typeface.DEFAULT, Typeface.NORMAL));
          
        // below line is used for setting text size
        // which we will be displaying in our PDF file.
        title.setTextSize(15);
          
        // below line is sued for setting color 
        // of our text inside our PDF file.
        title.setColor(ContextCompat.getColor(this, R.color.purple_200));
          
        // below line is used to draw text in our PDF file.
        // the first parameter is our text, second parameter 
        // is position from start, third parameter is position from top
        // and then we are passing our variable of paint which is title.
        canvas.drawText("A portal for IT professionals.", 209, 100, title);
        canvas.drawText("Geeks for Geeks", 209, 80, title);
  
        // similarly we are creating another text and in this 
        // we are aligning this text to center of our PDF file.
        title.setTypeface(Typeface.defaultFromStyle(Typeface.NORMAL));
        title.setColor(ContextCompat.getColor(this, R.color.purple_200));
        title.setTextSize(15);
          
        // below line is used for setting 
        // our text to center of PDF.
        title.setTextAlign(Paint.Align.CENTER);
        canvas.drawText("This is sample document which we have created.", 396, 560, title);
  
        // after adding all attributes to our 
        // PDF file we will be finishing our page.
        pdfDocument.finishPage(myPage);
          
        // below line is used to set the name of 
        // our PDF file and its path.
        File file = new File(Environment.getExternalStorageDirectory(), "GFG.pdf");
  
        try {
            // after creating a file name we will 
            // write our PDF file to that location.
            pdfDocument.writeTo(new FileOutputStream(file));
              
            // below line is to print toast message 
            // on completion of PDF generation.
            Toast.makeText(MainActivity.this, "PDF file generated succesfully.", Toast.LENGTH_SHORT).show();
        } catch (IOException e) {
            // below line is used
            // to handle error
            e.printStackTrace();
        }
        // after storing our pdf to that 
        // location we are closing our PDF file.
        pdfDocument.close();
    }
  
    private boolean checkPermission() {
        // checking of permissions.
        int permission1 = ContextCompat.checkSelfPermission(getApplicationContext(), WRITE_EXTERNAL_STORAGE);
        int permission2 = ContextCompat.checkSelfPermission(getApplicationContext(), READ_EXTERNAL_STORAGE);
        return permission1 == PackageManager.PERMISSION_GRANTED && permission2 == PackageManager.PERMISSION_GRANTED;
    }
  
    private void requestPermission() {
        // requesting permissions if not provided.
        ActivityCompat.requestPermissions(this, new String[]{WRITE_EXTERNAL_STORAGE, READ_EXTERNAL_STORAGE}, PERMISSION_REQUEST_CODE);
    }
  
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        if (requestCode == PERMISSION_REQUEST_CODE) {
            if (grantResults.length > 0) {
                  
                // after requesting permissions we are showing 
                // users a toast message of permission granted.
                boolean writeStorage = grantResults[0] == PackageManager.PERMISSION_GRANTED;
                boolean readStorage = grantResults[1] == PackageManager.PERMISSION_GRANTED;
  
                if (writeStorage && readStorage) {
                    Toast.makeText(this, "Permission Granted..", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(this, "Permission Denined.", Toast.LENGTH_SHORT).show();
                    finish();
                }
            }
        }
    }
}

输出：

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