java - 当我更改页面方向时出现在页面开头

Question

我正在使用barteksc-AndroidPdfViewer 。我正在使用这段代码

package com.github.barteksc.sample;

import android.content.ActivityNotFoundException;
import android.content.Intent;
import android.content.pm.PackageManager;
import android.database.Cursor;
import android.net.Uri;
import android.provider.OpenableColumns;
import android.support.annotation.NonNull;
import android.support.v4.app.ActivityCompat;
import android.support.v4.content.ContextCompat;
import android.support.v7.app.AppCompatActivity;
import android.util.Log;
import android.widget.Toast;

import com.github.barteksc.pdfviewer.PDFView;
import com.github.barteksc.pdfviewer.listener.OnLoadCompleteListener;
import com.github.barteksc.pdfviewer.listener.OnPageChangeListener;
import com.github.barteksc.pdfviewer.scroll.DefaultScrollHandle;
import com.shockwave.pdfium.PdfDocument;

import org.androidannotations.annotations.AfterViews;
import org.androidannotations.annotations.EActivity;
import org.androidannotations.annotations.NonConfigurationInstance;
import org.androidannotations.annotations.OnActivityResult;
import org.androidannotations.annotations.OptionsItem;
import org.androidannotations.annotations.OptionsMenu;
import org.androidannotations.annotations.ViewById;

import java.util.List;

@EActivity(R.layout.activity_main)
@OptionsMenu(R.menu.options)
public class PDFViewActivity extends AppCompatActivity implements OnPageChangeListener, OnLoadCompleteListener {

    private static final String TAG = PDFViewActivity.class.getSimpleName();

    private final static int REQUEST_CODE = 42;
    public static final int PERMISSION_CODE = 42042;

    public static final String SAMPLE_FILE = "sample.pdf";
    public static final String READ_EXTERNAL_STORAGE = "android.permission.READ_EXTERNAL_STORAGE";

    @ViewById
    PDFView pdfView;

    @NonConfigurationInstance
    Uri uri;

    @NonConfigurationInstance
    Integer pageNumber = 0;

    String pdfFileName;

    @OptionsItem(R.id.pickFile)
    void pickFile() {
        int permissionCheck = ContextCompat.checkSelfPermission(this,
                READ_EXTERNAL_STORAGE);

        if (permissionCheck != PackageManager.PERMISSION_GRANTED) {
            ActivityCompat.requestPermissions(
                    this,
                    new String[]{READ_EXTERNAL_STORAGE},
                    PERMISSION_CODE
            );

            return;
        }

        launchPicker();
    }

    void launchPicker() {
        Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
        intent.setType("application/pdf");
        try {
            startActivityForResult(intent, REQUEST_CODE);
        } catch (ActivityNotFoundException e) {
            //alert user that file manager not working
            Toast.makeText(this, R.string.toast_pick_file_error, Toast.LENGTH_SHORT).show();
        }
    }

    @AfterViews
    void afterViews() {
        if (uri != null) {
            displayFromUri(uri);
        } else {
            displayFromAsset(SAMPLE_FILE);
        }
        setTitle(pdfFileName);
    }

    private void displayFromAsset(String assetFileName) {
        pdfFileName = assetFileName;

        pdfView.fromAsset(SAMPLE_FILE)
                .defaultPage(pageNumber)
                .onPageChange(this)
                .enableAnnotationRendering(true)
                .onLoad(this)
                .scrollHandle(new DefaultScrollHandle(this))
                .load();
    }

    private void displayFromUri(Uri uri) {
        pdfFileName = getFileName(uri);

        pdfView.fromUri(uri)
                .defaultPage(pageNumber)
                .onPageChange(this)
                .enableAnnotationRendering(true)
                .onLoad(this)
                .scrollHandle(new DefaultScrollHandle(this))
                .load();
    }

    @OnActivityResult(REQUEST_CODE)
    public void onResult(int resultCode, Intent intent) {
        if (resultCode == RESULT_OK) {
            uri = intent.getData();
            displayFromUri(uri);
        }
    }

    @Override
    public void onPageChanged(int page, int pageCount) {
        pageNumber = page;
        setTitle(String.format("%s %s / %s", pdfFileName, page + 1, pageCount));
    }

    public String getFileName(Uri uri) {
        String result = null;
        if (uri.getScheme().equals("content")) {
            Cursor cursor = getContentResolver().query(uri, null, null, null, null);
            try {
                if (cursor != null && cursor.moveToFirst()) {
                    result = cursor.getString(cursor.getColumnIndex(OpenableColumns.DISPLAY_NAME));
                }
            } finally {
                if (cursor != null) {
                    cursor.close();
                }
            }
        }
        if (result == null) {
            result = uri.getLastPathSegment();
        }
        return result;
    }

    @Override
    public void loadComplete(int nbPages) {
        PdfDocument.Meta meta = pdfView.getDocumentMeta();
        Log.e(TAG, "title = " + meta.getTitle());
        Log.e(TAG, "author = " + meta.getAuthor());
        Log.e(TAG, "subject = " + meta.getSubject());
        Log.e(TAG, "keywords = " + meta.getKeywords());
        Log.e(TAG, "creator = " + meta.getCreator());
        Log.e(TAG, "producer = " + meta.getProducer());
        Log.e(TAG, "creationDate = " + meta.getCreationDate());
        Log.e(TAG, "modDate = " + meta.getModDate());

        printBookmarksTree(pdfView.getTableOfContents(), "-");

    }

    public void printBookmarksTree(List<PdfDocument.Bookmark> tree, String sep) {
        for (PdfDocument.Bookmark b : tree) {

            Log.e(TAG, String.format("%s %s, p %d", sep, b.getTitle(), b.getPageIdx()));

            if (b.hasChildren()) {
                printBookmarksTree(b.getChildren(), sep + "-");
            }
        }
    }

    /**
     * Listener for response to user permission request
     *
     * @param requestCode  Check that permission request code matches
     * @param permissions  Permissions that requested
     * @param grantResults Whether permissions granted
     */
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String permissions[],
                                           @NonNull int[] grantResults) {
        if (requestCode == PERMISSION_CODE) {
            if (grantResults.length > 0
                    && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
                launchPicker();
            }
        }
    }

}

更改页面方向。但是，如果我必须假设当我们开始横向时，纵向模式和页码 15 是否会改变页面的页面方向。

请帮我解决这个问题。

Answer 1

当您更改方向时，Android 将默认重新加载 Activity，这就是您丢失当前页面的原因。

有 2 种解决方案，一种是最佳实践，另一种可能有效，具体取决于具体情况。

解决方案1:

在 onSaveInstanceState 上保存最后一个已知页面，然后在 onCreate 上恢复该页面

protected void onSaveInstanceState(Bundle outState) {
  super.onSaveInstanceState(outState);
  outState.putInt("current_page", pageNumber);
}

public void onCreate(Bundle savedInstanceState) {
  if (savedInstanceState != null){
    pageNumber = savedInstanceState.getInt("current_page");
  }
}

解决方案2:

在 list 文件中设置 android:configChanges="orientation|screenSize" 属性。这将保留屏幕的状态，就像方向更改之前一样。

另请阅读 Activity 生命周期:https://developer.android.com/guide/components/activities/activity-lifecycle.html