应用程序启动时出现白屏

Question

我制作了一个从 url 加载图像并使用 CarouselWidget

在 coverflow 视图中显示它们的应用程序

当我运行我的应用程序第一次在 Genymotion 中时，它会下载数据库，从查询中获得结果，但不会构建 coverflow。当我运行第二次时，它会构建视图。为什么它不是第一次构建它？我在 onPostExecute 方法中包含了 coverflow 构建。
当我在真实设备上运行时，我总是看到白屏。当我运行它在设备上处于调试模式并确实退出时，它运行没问题。如果我没有收到任何错误，我该如何在设备上调试它？
如何动态加载图像？不是同时，而是在滑动的过程中。

这是我的代码。

    public class MainActivity extends AppCompatActivity {

    private static final String TAG = "qwe";
    public static final int DIALOG_DOWNLOAD_PROGRESS = 0;
    private static final String DB1_NAME = "SuperupDB.sqlite";
    private static final String DB2_NAME = "InventoryDB.sqlite";
    private static final String DB_URL = "https://storage.googleapis.com/shared_data/MKGn299XpJ6mn9c6/clientsync/db/SuperupDB.zip";
    private String dbQuery;
    private ProgressDialog mProgressDialog;

    private static String DB_PATH;

    private CoverFlowAdapter mAdapter;
    private ArrayList<Bitmap> mData = new ArrayList<>();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        if (android.os.Build.VERSION.SDK_INT >= 17) {
            DB_PATH = this.getApplicationInfo().dataDir + "/databases/";
        } else {
            DB_PATH = "/data/data/" + this.getPackageName() + "/databases/";
        }

        File dbFile1 = new File(DB_PATH + DB1_NAME);
        File dbFile2 = new File(DB_PATH + DB2_NAME);
        Log.d(TAG, dbFile1.getPath() + " " + dbFile1.exists());
        Log.d(TAG, dbFile2.getPath() + " " + dbFile2.exists());

        dbQuery = "Select p.PrdImgURL, cp.PrdID " +
                "from Products as p " +
                "inner join CategoryProduct_MM as cp " +
                "on p.PrdID = cp.PrdID " +
                "inner join InventoryDB.Facing as f " +
                "on p.PrdID = f.PrdID " +
                "where cp.CategoryID == 1 " +
                "and p.PrdImgURL is not null " +
                "order by f.`Order`";

        if (dbFile1.exists() && dbFile2.exists()) {
            loadProducts();
        } else {
            new DownloadDB().execute(DB_URL);
        }


    }

    private void loadProducts() {
        dbHandler dbh = dbHandler.getInstance(this);
        SQLiteDatabase db = dbh.getWritableDatabase();
        // attach second db to get products order from it
        db.execSQL("attach database ? as InventoryDB", new String[]{DB_PATH + DB2_NAME});
        db.beginTransaction();

        Cursor c = db.rawQuery(dbQuery, null);
        int count = c.getCount();
        String url[] = new String[count];
        int i = 0;


        while (c.moveToNext()) {
            url[i] = c.getString(c.getColumnIndex("PrdImgURL"));
            i++;
        }

        for (i = 0; i < url.length; i++) {
            loadBitmap(url[i]);
            Log.d(TAG, url[i]);
        }

        mAdapter = new CoverFlowAdapter(getApplicationContext());
        mAdapter.setData(mData);
        CoverFlowCarousel mCoverFlow = (CoverFlowCarousel) findViewById(R.id.coverflow);
        mCoverFlow.setAdapter(mAdapter);
    }

    private void loadBitmap(final String url) {
        RequestQueue queue = Volley.newRequestQueue(this);
        ImageRequest imageRequest = new ImageRequest(url,
                new Response.Listener<Bitmap>() {
                    @Override
                    public void onResponse(Bitmap bitmap) {
                        //mData.add(bitmap);
                        mData.add(addShadow(bitmap, bitmap.getHeight(), bitmap.getWidth(), Color.BLACK, 7, 3, 7));
                    }
                }, 0, 0, null,
                new Response.ErrorListener() {
                    public void onErrorResponse(VolleyError error) {
                        Log.d(TAG, "loadBitmap: " + error.toString());
                    }
                });
        queue.add(imageRequest);
    }

    public Bitmap addShadow(final Bitmap bm, final int dstHeight, final int dstWidth, int color, int size, float dx, float dy) {
        final Bitmap mask = Bitmap.createBitmap(dstWidth, dstHeight, Bitmap.Config.ALPHA_8);

        final Matrix scaleToFit = new Matrix();
        final RectF src = new RectF(0, 0, bm.getWidth(), bm.getHeight());
        final RectF dst = new RectF(0, 0, dstWidth - dx, dstHeight - dy);
        scaleToFit.setRectToRect(src, dst, Matrix.ScaleToFit.CENTER);

        final Matrix dropShadow = new Matrix(scaleToFit);
        dropShadow.postTranslate(dx, dy);

        final Canvas maskCanvas = new Canvas(mask);
        final Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);
        maskCanvas.drawBitmap(bm, scaleToFit, paint);
        paint.setXfermode(new PorterDuffXfermode(PorterDuff.Mode.MULTIPLY));
        maskCanvas.drawBitmap(bm, dropShadow, paint);

        final BlurMaskFilter filter = new BlurMaskFilter(size, BlurMaskFilter.Blur.NORMAL);
        paint.reset();
        paint.setAntiAlias(true);
        paint.setColor(color);
        paint.setMaskFilter(filter);
        paint.setFilterBitmap(true);

        final Bitmap ret = Bitmap.createBitmap(dstWidth + size, dstHeight + size, Bitmap.Config.ARGB_8888);
        final Canvas retCanvas = new Canvas(ret);
        retCanvas.drawBitmap(mask, 0, 0, paint);
        retCanvas.drawBitmap(bm, scaleToFit, null);
        mask.recycle();
        return ret;
    }

    @Override
    protected Dialog onCreateDialog(int id) {
        switch (id) {
            case DIALOG_DOWNLOAD_PROGRESS:
                mProgressDialog = new ProgressDialog(this);
                mProgressDialog.setMessage("Loading database..");
                mProgressDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
                mProgressDialog.setCancelable(false);
                mProgressDialog.show();
                return mProgressDialog;
            default:
                return null;
        }
    }

    class DownloadDB extends AsyncTask<String, String, String> {

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            showDialog(DIALOG_DOWNLOAD_PROGRESS);
        }

        @Override
        protected String doInBackground(String... aurl) {
            int count;

            try {

                URL url = new URL(aurl[0]);
                URLConnection conn = url.openConnection();
                conn.connect();

                long lengthOfFile = conn.getContentLength();
                Log.d(TAG, "Length of file: " + lengthOfFile);

                InputStream input = new BufferedInputStream(url.openStream());
                ZipInputStream zis = new ZipInputStream(input);

                //default database directory
                File dbDir = new File(DB_PATH);
                if (!dbDir.exists())
                    dbDir.mkdir();

                try {
                    ZipEntry ze;
                    while ((ze = zis.getNextEntry()) != null) {
                        if (ze.getName().equals(DB1_NAME) || ze.getName().equals(DB2_NAME)) {
                            lengthOfFile = ze.getSize();
                            FileOutputStream fout = new FileOutputStream(new File(dbDir, ze.getName()));
                            byte[] data = new byte[1024];
                            long total = 0;
                            while ((count = zis.read(data)) != -1) {
                                total += count;
                                publishProgress("" + (int) ((total * 100) / lengthOfFile));
                                fout.write(data, 0, count);
                            }
                            zis.closeEntry();
                            fout.close();
                        }
                    }
                } catch (Exception e) {
                    Log.d(TAG, e.toString());
                } finally {
                    zis.close();
                }

            } catch (Exception e) {
                Log.d(TAG, e.toString());
            }
            return null;

        }

        protected void onProgressUpdate(String... progress) {
            Log.d(TAG, progress[0]);
            mProgressDialog.setProgress(Integer.parseInt(progress[0]));
        }

        @Override
        protected void onPostExecute(String unused) {
            dismissDialog(DIALOG_DOWNLOAD_PROGRESS);
            loadProducts();
        }
    }
}


    public class dbHandler extends SQLiteOpenHelper {
    private static final int VERSION = 1;
    private static final String DATABASE_NAME = "SuperupDB.sqlite";
    private static final String TAG = "qwe";
    private static File DATABASE_FILE;

    // This is an indicator if we need to copy the
    // database file.
    private boolean mInvalidDatabaseFile = false;
    private boolean mIsUpgraded = false;
    private Context mContext;

    /**
     * number of users of the database connection.
     */
    private int mOpenConnections = 0;

    private static dbHandler mInstance;

    synchronized static public dbHandler getInstance(Context context) {
        if (mInstance == null) {
            mInstance = new dbHandler(context.getApplicationContext());
        }
        return mInstance;
    }

    private dbHandler(Context context) {
        super(context, DATABASE_NAME, null, VERSION);
        this.mContext = context;
        SQLiteDatabase db = null;
        try {
            db = getReadableDatabase();
            if (db != null) {
                db.close();
            }

            DATABASE_FILE = context.getDatabasePath(DATABASE_NAME);

/*            if (mInvalidDatabaseFile) {
                //copyDatabase();
                Log.d(TAG, "Where is db?");
            }*/
            if (mIsUpgraded) {
                doUpgrade();
            }
        } catch (SQLiteException e) {
        } finally {
            if (db != null && db.isOpen()) {
                db.close();
            }
        }
    }

    @Override
    public void onCreate(SQLiteDatabase db) {
        //mInvalidDatabaseFile = true;

    }

    @Override
    public void onUpgrade(SQLiteDatabase database,
                          int old_version, int new_version) {
        //mInvalidDatabaseFile = true;
        mIsUpgraded = true;

    }

    /**
     * called if a database upgrade is needed
     */
    private void doUpgrade() {
        // implement the database upgrade here.
    }

    @Override
    public synchronized void onOpen(SQLiteDatabase db) {
        super.onOpen(db);
        // increment the number of users of the database connection.
        mOpenConnections++;
        if (!db.isReadOnly()) {
            // Enable foreign key constraints
            db.execSQL("PRAGMA foreign_keys=ON;");
        }
    }

    /**
     * implementation to avoid closing the database connection while it is in
     * use by others.
     */
    @Override
    public synchronized void close() {
        mOpenConnections--;
        if (mOpenConnections == 0) {
            super.close();
        }
    }

    private void setDatabaseVersion() {
        SQLiteDatabase db = null;
        try {
            db = SQLiteDatabase.openDatabase(DATABASE_FILE.getAbsolutePath(), null,
                    SQLiteDatabase.OPEN_READWRITE);
            db.execSQL("PRAGMA user_version = " + VERSION);
        } catch (SQLiteException e) {
        } finally {
            if (db != null && db.isOpen()) {
                db.close();
            }
        }
    }

}

Answer 1

通过 Universal Image Loader 延迟加载图像解决了这个问题。
Here is the example

Answer 2

另一种解决此问题的方法是在应用的 style.xml 文件中添加以下行：

<item name="android:windowDisablePreview">true</item>

应用程序启动时出现白屏

App starts with white screen

android

coverflow

android-asynctask