在App内实现直接预览pdf文件，而不是通过调用第三方软件，如WPS office等打开pdf。

主要思路：通过PhotoView将pdf读取为图片流进行展示。

一、首先，获取对本地文件读取的权限

在AndrooidManifest.xml中声明权限，以及页面中动态获取权限。

二、在build.gradle中引入需要的包

    implementation 'com.github.chrisbanes:PhotoView:2.0.0'

三、在项目库地址中添加

以及：

四、添加页面布局文件

添加一个页面布局文件：activity_pdf.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"android:orientation="vertical"><android.support.v4.view.ViewPagerandroid:id="@+id/vp_pdf"android:layout_width="match_parent"android:layout_height="wrap_content"></android.support.v4.view.ViewPager></LinearLayout >

添加一个适配器布局：item_pdf.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:orientation="vertical" android:layout_width="match_parent"android:layout_height="match_parent"><com.github.chrisbanes.photoview.PhotoViewandroid:id="@+id/iv_pdf"android:layout_width="match_parent"android:layout_height="match_parent"></com.github.chrisbanes.photoview.PhotoView></LinearLayout>

五、打开和关闭的实现代码

public class PdfActivity extends AppCompatActivity {LayoutInflater mInflater;PdfRenderer mRenderer;ViewPager vpPdf;ParcelFileDescriptor mDescriptor;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_pdf);init();}public void init() {mInflater = LayoutInflater.from(this);vpPdf =findViewById(R.id.vp_pdf);try {openRender();} catch (IOException e) {e.printStackTrace();}}@TargetApi(Build.VERSION_CODES.LOLLIPOP)private void openRender() throws IOException {File file = new File(DataHelper.GetHelpPdfPath());//初始化PdfRendermDescriptor = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);if (mDescriptor != null) {mRenderer = new PdfRenderer(mDescriptor);}//初始化ViewPager的适配器并绑定MyAdapter adapter = new MyAdapter();vpPdf.setAdapter(adapter);}class MyAdapter extends PagerAdapter {@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)@Overridepublic int getCount() {return mRenderer.getPageCount();}@Overridepublic boolean isViewFromObject(View view, Object object) {return view==object;}@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)@Overridepublic Object instantiateItem(ViewGroup container, int position) {View view = mInflater.inflate(R.layout.item_pdf, null);PhotoView pvPdf = view.findViewById(R.id.iv_pdf);pvPdf.setEnabled(true);if (getCount() <= position) {return view;}PdfRenderer.Page currentPage = mRenderer.openPage(position);Bitmap bitmap = Bitmap.createBitmap(1080, 1760, Bitmap.Config.ARGB_8888);currentPage.render(bitmap, null, null, PdfRenderer.Page.RENDER_MODE_FOR_DISPLAY);pvPdf.setImageBitmap(bitmap);//关闭当前Page对象currentPage.close();container.addView(view);return view;}@Overridepublic void destroyItem(ViewGroup container, int position, Object object) {//销毁需要销毁的视图container.removeView((View) object);}}
//关闭pdf@Overrideprotected void onDestroy() {super.onDestroy();try{closeRenderer();}catch (Exception ex){ex.printStackTrace();}}//关闭pdf@RequiresApi(api = Build.VERSION_CODES.LOLLIPOP)private void closeRenderer() throws IOException {if (mRenderer != null){mRenderer.close();}if (mDescriptor != null){mDescriptor.close();}}}