无法在Android Studio中打开PDF

Question

我正在开发API 27中的应用程序，我在从资产文件夹打开PDF时遇到问题。我尝试了很多不同的方法，但仍然没有成功。

PDF打开时，会出现一个空白的黑屏。我在其返回的所有步骤中检查了file.exist() return false'false'。

我真的需要有关此主题的帮助。另外，我尝试了内部和外部存储。还尝试了不同的意图标签。但仍然没有运气。

这是我用过的功能。

private void openPDFFiles(String fileName) //fileName is the pdf file name which is keep in assets folder. ex file.pdf
{
    AssetManager assetManager = getApplicationContext().getAssets();
    InputStream in = null;
    OutputStream out = null;
    File imagePath = new File(getFilesDir(), "Videos");
    File file = new File(imagePath, "1.pdf");
    try {
        in = assetManager.open(fileName);
        out = openFileOutput(file.getName(), MODE_PRIVATE);

        copyFile(in, out);
        in.close();
        in = null;
        out.flush();
        out.close();
        out = null;
    } catch (Exception e) {
        System.out.println(e);
    }

    try {
        Intent intent = new Intent(Intent.ACTION_VIEW);
        intent.setDataAndType(FileProvider.getUriForFile(getApplicationContext(), "com.administrator.siemens.android.fileprovider", file), "application/pdf");
        //intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
        //intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
        //intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
        //intent.addFlags(Intent.FLAG_ACTIVITY_NO_HISTORY);
        intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK|Intent.FLAG_GRANT_READ_URI_PERMISSION);
        startActivity(intent);
    } catch (RuntimeException ex) {
        Toast.makeText(Document.this, "There's no PDF Reader found in your device", Toast.LENGTH_SHORT).show();
    }

    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);
        }
        System.out.println("1222222222");
    }

的manifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.administrator.siemens">
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/me"
        android:label="@string/app_name"
        android:roundIcon="@mipmap/ic_launcher_round"
        android:supportsRtl="true"
        android:theme="@style/AppTheme">
        <provider
            android:name="android.support.v4.content.FileProvider"
            android:authorities="com.administrator.siemens.android.fileprovider"
            android:grantUriPermissions="true"
            android:exported="false">
            <meta-data
                android:name="android.support.FILE_PROVIDER_PATHS"
                android:resource="@xml/filepath" />
        </provider>
        <activity android:name=".MainActivity">
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

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

filepath.xml：

<paths>
    <files-path name="my_docs" path="Videos/"/>
</paths>

非常感谢！如果有人能帮助我的话。