PDF数据在Android上显示为空白

Question

我在早期版本的Android上使用file //。因此，当我更新sdk目标版本时，我的应用程序停止打开pdf。相反，它开始崩溃。

因此，我在网上浏览了一些解决方案，发现file：//已过时，content：//已被使用。

因此，我对代码进行了以下更改。 我的应用程序停止崩溃，并且pdf开始打开，但是应用程序每次都出现黑屏。

以下是我的代码。

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    package="in.sp.existingpdfread">

    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application
        android:allowBackup="true"
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme"
        tools:ignore="GoogleAppIndexingWarning">

        <provider
            android:name="android.support.v4.content.FileProvider"
            android:authorities="${applicationId}.myfileprovider"
            android:exported="false"
            android:grantUriPermissions="true">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/file_provider_paths"/>
        </provider>

        <activity
            android:name=".MainActivity"
            android:label="@string/app_name"
            android:theme="@style/AppTheme.NoActionBar">

        </activity>
        <activity android:name=".PDFActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>

res / xml / file_provider_path.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
    xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".PDFActivity"
    android:orientation="vertical">

    <TextView
        android:id="@+id/section_label"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Click This Button"/>

    <Button
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:id="@+id/button1"
        android:text="Click Here"
        android:background="@color/colorPrimaryDark"
        android:textColor="@color/colorAccent"
        android:onClick="readpdf"/>

</LinearLayout>

PDFActivity.java

package in.sp.existingpdfread;

import android.content.ActivityNotFoundException;
import android.content.Context;
import android.content.Intent;
import android.content.res.AssetManager;
import android.net.Uri;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.widget.Button;

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

public class PDFActivity extends AppCompatActivity {

    Context context;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_pdf);
        context=this;

    }
    public void readpdf(View view)
    {
        AssetManager assetManager = getAssets();

        InputStream in = null;
        OutputStream out = null;
        File file = new File(getFilesDir(), "pdf/calender.pdf");
        try
        {
            in = assetManager.open("pdf/calender.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());
        }
        Intent target = new Intent(Intent.ACTION_VIEW);
        //target.setDataAndType(Uri.fromFile(file),"application/pdf");
        target.setDataAndType(
                Uri.parse("content://" + getFilesDir() + "/pdf/calender.pdf"),
                "application/pdf");
        target.setFlags(Intent.FLAG_ACTIVITY_NO_HISTORY);

        Intent intent = Intent.createChooser(target, "Open File");
        try {
            startActivity(intent);
        } catch (ActivityNotFoundException e) {
            // Instruct the user to install a PDF reader here, or something
        }

    }

    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);
        }
    }

}

并且我已经将pdf保存在资产文件夹中