Android專案實戰（六十一）：pdf檔案用圖片方式預覽

前言：

Android不支持pdf的在線預覽，網上有多種預覽pdf的實作方式，點此查看總結

這里實作一種先下載pdf檔案到本地，再將檔案轉成圖片顯示的的操作 

一個工具類：

import android.app.Application;
import android.arch.lifecycle.AndroidViewModel;
import android.arch.lifecycle.LiveData;
import android.arch.lifecycle.MutableLiveData;
import android.graphics.Bitmap;
import android.graphics.pdf.PdfRenderer;
import android.os.ParcelFileDescriptor;
import android.support.annotation.WorkerThread;
import android.util.Log;
import android.widget.ImageView;

import java.io.File;
import java.io.IOException;
import java.util.concurrent.Executor;
import java.util.concurrent.Executors;
import java.util.concurrent.TimeUnit;

import info.ecloud.core.util.ToastUtils;
import info.ecloud.merchant.app.BaseObserve;
import io.reactivex.Observable;
import io.reactivex.android.schedulers.AndroidSchedulers;
import io.reactivex.schedulers.Schedulers;

public class PdfRendererBasicViewModel extends AndroidViewModel {
    private static final String TAG = "PdfRendererBasic";

    /**
     * The filename of the PDF.
     */
    private static final String FILENAME = "sample.pdf";

    private final MutableLiveData<PageInfo> mPageInfo = new MutableLiveData<>();
    private final MutableLiveData<Bitmap> mPageBitmap = new MutableLiveData<>();
    private final MutableLiveData<Boolean> mPreviousEnabled = new MutableLiveData<>();
    private final MutableLiveData<Boolean> mNextEnabled = new MutableLiveData<>();

    private final Executor mExecutor;
    private ParcelFileDescriptor mFileDescriptor;
    private PdfRenderer mPdfRenderer;
    private PdfRenderer.Page mCurrentPage;
    private boolean mCleared;
    public File pdfFile ;
    public ImageView pdfView ;


    @SuppressWarnings("unused")
    public PdfRendererBasicViewModel(Application application , File pdfFile , ImageView pdfView) {
        this(application, false);
        this.pdfFile = pdfFile;
        this.pdfView = pdfView;
    }

    PdfRendererBasicViewModel(Application application, boolean useInstantExecutor) {
        super(application);
        if (useInstantExecutor) {
            mExecutor = Runnable::run;
        } else {
            mExecutor = Executors.newSingleThreadExecutor();
        }
        mExecutor.execute(() -> {
            try {
                openPdfRenderer();
                showPage(0);
                if (mCleared) {
                    closePdfRenderer();
                }
            } catch (IOException e) {
                Log.e(TAG, "Failed to open PdfRenderer", e);
            }
        });
    }

    @Override
    protected void onCleared() {
        super.onCleared();
        mExecutor.execute(() -> {
            try {
                closePdfRenderer();
                mCleared = true;
            } catch (IOException e) {
                Log.i(TAG, "Failed to close PdfRenderer", e);
            }
        });
    }

    public LiveData<PageInfo> getPageInfo() {
        return mPageInfo;
    }

    public LiveData<Bitmap> getPageBitmap() {
        Log.i("xqxinfo","bitmap==>"+(mPageBitmap==null));
        return mPageBitmap;
    }

    public LiveData<Boolean> getPreviousEnabled() {
        return mPreviousEnabled;
    }

    public LiveData<Boolean> getNextEnabled() {
        return mNextEnabled;
    }

    void showPrevious() {
        if (mPdfRenderer == null || mCurrentPage == null) {
            return;
        }
        final int index = mCurrentPage.getIndex();
        if (index > 0) {
            mExecutor.execute(() -> showPage(index - 1));
        }
    }

    public void showNext() {
        if (mPdfRenderer == null || mCurrentPage == null) {
            return;
        }
        final int index = mCurrentPage.getIndex();
        if (index + 1 < mPdfRenderer.getPageCount()) {
            mExecutor.execute(() -> showPage(index + 1));
        }
    }
    public void showLast() {
        if (mPdfRenderer == null || mCurrentPage == null) {
            return;
        }
        final int index = mCurrentPage.getIndex();
        if (index - 1 >=0) {
            mExecutor.execute(() -> showPage(index - 1));
        }
    }

    @WorkerThread
    private void openPdfRenderer() throws IOException {
        final File file = pdfFile;
        if (!file.exists()) {
            ToastUtils.showLong("檔案預覽失敗");
            return;
        }
        Log.i("xqxinfo","file->"+file.getAbsolutePath());
        mFileDescriptor = ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
        if (mFileDescriptor != null) {
            mPdfRenderer = new PdfRenderer(mFileDescriptor);
        }
    }

    @WorkerThread
    private void closePdfRenderer() throws IOException {
        if (mCurrentPage != null) {
            mCurrentPage.close();
        }
        if (mPdfRenderer != null) {
            mPdfRenderer.close();
        }
        if (mFileDescriptor != null) {
            mFileDescriptor.close();
        }
    }

    @WorkerThread
    private void showPage(int index) {
        // Make sure to close the current page before opening another one.
        if (null != mCurrentPage) {
            mCurrentPage.close();
        }
        // Use `openPage` to open a specific page in PDF.
        mCurrentPage = mPdfRenderer.openPage(index);
        Bitmap bitmap = Bitmap.createBitmap(mCurrentPage.getWidth(), mCurrentPage.getHeight(),
                Bitmap.Config.ARGB_8888);
        // Here, we render the page onto the Bitmap.
        // To render a portion of the page, use the second and third parameter. Pass nulls to get
        // the default result.
        // Pass either RENDER_MODE_FOR_DISPLAY or RENDER_MODE_FOR_PRINT for the last parameter.
        mCurrentPage.render(bitmap, null, null, PdfRenderer.Page.RENDER_MODE_FOR_PRINT);
        mPageBitmap.postValue(bitmap);
        Observable.timer(10, TimeUnit.MILLISECONDS).subscribeOn(Schedulers.io())
                .observeOn(AndroidSchedulers.mainThread())
                .subscribe(new BaseObserve<Long>() {
                    @Override
                    public void onNext(Long aLong) {
                        pdfView.setImageBitmap(bitmap);
                    }
                });
        final int count = mPdfRenderer.getPageCount();
        mPageInfo.postValue(new PageInfo(index, count));
        mPreviousEnabled.postValue(index > 0);
        mNextEnabled.postValue(index + 1 < count);
    }

    static class PageInfo {
        final int index;
        final int count;

        PageInfo(int index, int count) {
            this.index = index;
            this.count = count;
        }
    }
}

使用方法：

public PdfRendererBasicViewModel(Application application , File pdfFile , ImageView pdfView) 

注意，因為是圖片方式顯示，依賴于一個ImageView , 每次只顯示pdf一頁的資料預覽，額外提供上一頁、下一頁的方法使用

 這里只提供基本使用，可以自行拓展功能，不限于圖片縮放，多頁展示等

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