启动时不显示第一页答案

【问题标题】：Not showing the first page when started启动时不显示第一页
【发布时间】：2016-05-16 12:45:08
【问题描述】：

美好的一天，我几乎是 android studio 上的 pdf 渲染器的新手 > api 21，我找到了一个简单的代码来读取资产文件夹上的 pdf。我的问题是，当它加载时，文件的第一页没有显示，除非我按下下一步按钮。我的应用程序旨在阅读用户手册 pdf。

package com.bloxofcode.phase1app;

import android.app.AlertDialog;
import android.content.Context;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.Matrix;
import android.graphics.Rect;
import android.graphics.pdf.PdfRenderer;
import android.os.ParcelFileDescriptor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class UsersManual extends AppCompatActivity {

    private ImageView imageView;
    private int currentPage = 0;
    private Button next, previous;

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

        next = (Button) findViewById(R.id.next);
        previous = (Button) findViewById(R.id.previous);
        render();
        next.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                currentPage++;
                render();
            }
        });

        previous.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                currentPage--;
                render();
            }
        });


    }

    private void render() {
        try{
            imageView = (ImageView) findViewById(R.id.image);
            int REQ_WIDTH = imageView.getWidth();
            int REQ_HEIGHT = imageView.getHeight();

            Bitmap bitmap = Bitmap.createBitmap(REQ_WIDTH, REQ_HEIGHT, Bitmap.Config.ARGB_8888);
            //File file = new File("/sdcard/Download/sample.pdf");

            AssetManager assetManager = getAssets();

            InputStream in = null;
            OutputStream out = null;
            File file = new File(getFilesDir(), "Learning Python 5th Ed 2013.pdf");
            try
            {
                in = assetManager.open("Learning Python 5th Ed 2013.pdf");
                out = openFileOutput(file.getName(), Context.MODE_WORLD_READABLE);

                copyFile(in, out);
                in.close();
                in = null;
                out.flush();
                out.close();
                out = null;
            } catch (Exception e)
            {
                Log.e("tag", e.getMessage());
            }
            //ParcelFileDescriptor p = getApplicationContext().getAssets().openFd("Learning Python 5th Ed 2013.pdf").getParcelFileDescriptor();
            File f = new File(getFilesDir() + "/Learning Python 5th Ed 2013.pdf");
            PdfRenderer renderer = new PdfRenderer(ParcelFileDescriptor.open(f, ParcelFileDescriptor.MODE_READ_ONLY));

            if(currentPage <= 0) {
                currentPage = 0;
            } else if(currentPage > renderer.getPageCount()) {
                currentPage = renderer.getPageCount() - 1;
            }

            Matrix m = imageView.getImageMatrix();
            Rect rect = new Rect(0, 0, REQ_WIDTH, REQ_HEIGHT);
            renderer.openPage(currentPage).render(bitmap,rect, null, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY);
            imageView.setImageMatrix(m);
            imageView.setImageBitmap(bitmap);
            imageView.invalidate();

        } catch(Exception e) {
            e.printStackTrace();
        }
    }

    private void copyFile(InputStream in, OutputStream out) throws IOException
    {
        byte[] buffer = new byte[1024];
        int read;
        while ((read = in.read(buffer)) != -1)
        {
            out.write(buffer, 0, read);
        }
    }
}

【问题讨论】：

如果在渲染前增加 onCreate 中的页面计数器会怎样？
还是不行:(
我不明白为什么不这样做。启动活动和计时按钮之间的区别在于增加页面并再次调用渲染。也许你实际上需要调用render，增加计数器，然后在onCreate中再次渲染

标签： android pdf android-studio

【解决方案1】：

REQ_WIDTH 和 REQ_HEIGHT 为 0。尝试向它们添加与屏幕尺寸相关的值

【讨论】：

【解决方案2】：

你能试试这段代码吗？我刚刚清理了一下

import android.app.AlertDialog;
import android.content.Context;
import android.content.res.AssetManager;
import android.graphics.Bitmap;
import android.graphics.Matrix;
import android.graphics.Rect;
import android.graphics.pdf.PdfRenderer;
import android.os.ParcelFileDescriptor;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.widget.Button;
import android.widget.ImageView;

import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;

public class UsersManual extends AppCompatActivity {

    private ImageView imageView;
    private int currentPage = 0;
    private Button next, previous;
    private PdfRenderer renderer;
    int REQ_WIDTH = imageView.getWidth();
    int REQ_HEIGHT = imageView.getHeight();
    private int count;

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

        next = (Button) findViewById(R.id.next);
        previous = (Button) findViewById(R.id.previous);
        render();
        display();
        next.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                currentPage++;
                display();
            }
        });

        previous.setOnClickListener(new View.OnClickListener() {

            @Override
            public void onClick(View v) {
                currentPage--;
                display();
            }
        });


    }

    private void render() {
        try {
            imageView = (ImageView) findViewById(R.id.image);
            REQ_WIDTH = imageView.getWidth();
            REQ_HEIGHT = imageView.getHeight();

            File f = new File(getFilesDir() + "/Learning Python 5th Ed 2013.pdf");
            renderer = new PdfRenderer(ParcelFileDescriptor.open(f, ParcelFileDescriptor.MODE_READ_ONLY));
            count = renderer.getPageCount();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    private void display(){

        if (currentPage <= 0) {
            currentPage = 0;
        } else if (currentPage > count) {
            currentPage = renderer.getPageCount() - 1;
        }

        Bitmap bitmap = Bitmap.createBitmap(REQ_WIDTH, REQ_HEIGHT, Bitmap.Config.ARGB_8888);

        Matrix m = imageView.getImageMatrix();
        Rect rect = new Rect(0, 0, REQ_WIDTH, REQ_HEIGHT);
        renderer.openPage(currentPage).render(bitmap, rect, null, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY);
        imageView.setImageMatrix(m);
        imageView.setImageBitmap(bitmap);
        imageView.invalidate();
    }


}

【讨论】：