Question

我试过了：

package com.example.dell.pdfreader;

import android.content.Context;
import android.graphics.Bitmap;
import android.graphics.Matrix;
import android.graphics.Rect;
import android.graphics.pdf.PdfRenderer;
import android.net.Uri;
import android.os.ParcelFileDescriptor;
import android.support.v7.app.AlertDialog;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;
import android.widget.Toast;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class MainActivity extends AppCompatActivity {

    private ImageView img;
    private int currentpage = 0;
    private Button next, previous;
    File file;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        next = (Button) findViewById(R.id.next);
        previous = (Button) findViewById(R.id.previous);
       //  file=getFile();


        next.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                currentpage++;
                render(file);
            }
        });


        previous.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                currentpage--;
                render(file);
            }
        });
    }

    private void render(File file) {

        try {

            img = (ImageView) findViewById(R.id.image);

            int width = img.getWidth();
            int height = img.getHeight();

            Bitmap bitmap = Bitmap.createBitmap(width, height, Bitmap.Config.ARGB_4444);





            PdfRenderer renderer = new PdfRenderer(ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY));

            if (currentpage < 0) {
                currentpage = 0;

            } else if (currentpage > renderer.getPageCount()) {


                currentpage = renderer.getPageCount() - 1;

                Matrix matrix = img.getImageMatrix();

                Rect rect = new Rect(0, 0, width, height);

                renderer.openPage(currentpage).render(bitmap, rect, matrix, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY);

                img.setImageMatrix(matrix);
                img.setImageBitmap(bitmap);
                img.invalidate();

            }


        } catch (Exception e) {

            e.printStackTrace();


        }
    }

    private File getFile() {
        File file=new File(this.getExternalFilesDir(null),"Example.pdf");;
        byte buffer[]=null;
        OutputStream output = null;


        InputStream input = null;
        try {
            input = this.getAssets().open("Example.pdf");

            buffer = new byte[input.available()];
            input.read(buffer);
            output = new FileOutputStream(file);
            output.write(buffer);
        }
        catch(FileNotFoundException e){
            e.printStackTrace();
            Toast.makeText(this,"File not Found",Toast.LENGTH_LONG).show();
            return null;
        }
        catch (IOException e) {
            e.printStackTrace();
            Toast.makeText(this,"Failed to open",Toast.LENGTH_LONG).show();
            return null;
        }

    return file;
    }
}

以上代码生成以下错误：

> java.lang.NullPointerException: Attempt to invoke virtual method
> 'java.lang.String java.io.File.getPath()' on a null object reference
> 03-18 15:42:16.245 6826-6826/com.example.dell.pdfreader W/System.err: 
> at
> android.os.ParcelFileDescriptor.openInternal(ParcelFileDescriptor.java:269)
> 03-18 15:42:16.245 6826-6826/com.example.dell.pdfreader W/System.err: 
> at android.os.ParcelFileDescriptor.open(ParcelFileDescriptor.java:200)
> 03-18 15:42:16.246 6826-6826/com.example.dell.pdfreader W/System.err: 
> at
> com.example.dell.pdfreader.MainActivity.render(MainActivity.java:76)
> 03-18 15:42:16.246 6826-6826/com.example.dell.pdfreader W/System.err: 
> at
> com.example.dell.pdfreader.MainActivity.access$100(MainActivity.java:26)
> 03-18 15:42:16.246 6826-6826/com.example.dell.pdfreader W/System.err: 
> at
> com.example.dell.pdfreader.MainActivity$1.onClick(MainActivity.java:47)
> 03-18 15:42:16.246 6826-6826/com.example.dell.pdfreader W/System.err: 
> at android.view.View.performClick(View.java:5265) 03-18 15:42:16.246
> 6826-6826/com.example.dell.pdfreader W/System.err:     at
> android.view.View$PerformClick.run(View.java:21534) 03-18 15:42:16.246
> 6826-6826/com.example.dell.pdfreader W/System.err:     at
> android.os.Handler.handleCallback(Handler.java:815) 03-18 15:42:16.247
> 6826-6826/com.example.dell.pdfreader W/System.err:     at
> android.os.Handler.dispatchMessage(Handler.java:104) 03-18
> 15:42:16.247 6826-6826/com.example.dell.pdfreader W/System.err:     at
> android.os.Looper.loop(Looper.java:207) 03-18 15:42:16.247
> 6826-6826/com.example.dell.pdfreader W/System.err:     at
> android.app.ActivityThread.main(ActivityThread.java:5728) 03-18
> 15:42:16.247 6826-6826/com.example.dell.pdfreader W/System.err:     at
> java.lang.reflect.Method.invoke(Native Method) 03-18 15:42:16.247
> 6826-6826/com.example.dell.pdfreader W/System.err:     at
> com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:789)
> 03-18 15:42:16.247 6826-6826/com.example.dell.pdfreader W/System.err: 
> at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:679)

Answer 1

首先，正如评论中所述，file是null，因为您从未在其上设置过值。

其次，对于资产中的PDF，没有文件。使用openFd()上的AssetManager获取资产上的AssetFileDescriptor，然后致电getParcelFileDescriptor()上的AssetFileDescriptor获取ParcelFileDescriptor。

第三，PdfRenderer不处理任意PDF文件。它只用于打印预览，仅此而已。最有可能的是，您需要使用here。

如何制作pdf Reader Android应用程序从资产文件夹中获取pdf？

1 个答案: