Question

当前正在开发一个微型应用程序，其目标是再现Android图库，但我的应用程序无法正常工作。

事实上，由于只能使用画布而没有使用任何布局的权利，我按照不同的步骤进行操作，现在我将向您解释这些步骤，以说明问题：

1-我的主要活动是运行两个对象，即两个个人类的“ Scan”对象和“ GalleryView”对象

2-扫描对象使用功能检索图库中图像的所有路径。

3-MainActivity恢复此数组列表，并将其传递给我的galleryview的生成器。

4-画廊视图知道要显示的元素数量（等于扫描返回的字符串arraylist的大小），并构建每个图像的位图以便显示它们

那就是问题所在。确实，我的手机上一共显示了约480张图像，所以我浏览GalleryView.java路径列表的位置是一个问题，因为它使应用程序崩溃。

如果我决定只绘制第一张图像的480倍，那么它将起作用。

所以我想知道如何优化此行为以避免崩溃和内存过载。

我的老师建议我们使用BitmapDrawable代替Bitmap，但我不知道如何实现。

您将在我的应用程序的所有类下找到+大致解释渲染步骤的图

MainActivity.java


public class MainActivity extends AppCompatActivity {


    //Objet qui va nous permettre de récuperer les images de la gallerie du téléphone
    ScanPictures m_scan;

    //liste des chemins des images de la gallerie
    ArrayList<String>m_paths;

    //objet qui permet d'afficher les images
    GalleryView m_gallery;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);

        //On créer l'object scanner pour récuperer les photos de la gallerie
        m_scan = new ScanPictures(this.getApplicationContext());

        //Boolean nous indiquant si l'application à l'autorisation d'accéder au contenu interne du téléphone
        Boolean isAuthorized = this.isReadStoragePermissionGranted();

        //Si on est authorisé, on scan la gallerie et on récuperer les chemins des photos
        if(isAuthorized){
            System.out.println("SCAN IMAGES ALREADY GRANTED");
            m_paths = m_scan.getImages();
            System.out.println("SCAN IMAGES ALREADY GRANTED DONE");
        }

        m_gallery = new GalleryView(this.getApplicationContext(),m_paths);
        m_gallery.setPicturesNumber(m_paths.size());
        setContentView(m_gallery);

    }

    public  boolean isReadStoragePermissionGranted() {
        if (Build.VERSION.SDK_INT >= 23) { //le sdk est supérieur a 23, l'autorisation n'est pas donnée automatiquement
            if (checkSelfPermission(Manifest.permission.READ_EXTERNAL_STORAGE)
                    == PackageManager.PERMISSION_GRANTED) {
                return true;
            } else {

                //L'autorisation n'est pas accordée, on la demande à l'utilisateur
                ActivityCompat.requestPermissions(this, new String[]{Manifest.permission.READ_EXTERNAL_STORAGE}, 3);
                return false;
            }
        }
        else { //les permissions sont automatiquement données en sdk < 23
            return true;
        }
    }


    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (grantResults.length > 0 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            //SI l'utilisateur à donner l'autorisation, on scan les photos
            if (requestCode == 3 ) {
                System.out.println("SCAN IMAGES FIRST GRANTED");
                this.m_scan.getImages();
                System.out.println("SCAN IMAGES FIRST GRANTED DONE");
            }
        }
    }
}

GalleryView.java

public class GalleryView extends View {

    private GestureDetector mGestureDetector;
    private ScaleGestureDetector mScaleGestureDetector;
    private float mScale = 1;
    private Bitmap resized =null;
    private int numColumns, numRows, nbPict;
    private int cellSize;
    private ArrayList<String> m_paths;
    private Context m_context;

    public GalleryView(Context context, ArrayList<String> paths) {
        super(context);

        m_context = context;
        m_paths = paths;
        numColumns = 7;
        mGestureDetector = new GestureDetector(context, new ZoomGesture());
        mScaleGestureDetector = new ScaleGestureDetector(context, new ScaleGesture());
    }

    public void setPicturesNumber(int nbPict) {
        this.nbPict = nbPict;
        calculateDimensions();
    }


    private void calculateDimensions() {
        numRows = nbPict/numColumns;
        cellSize = getWidth() / numColumns;
        invalidate();

    }

    @Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        super.onSizeChanged(w, h, oldw, oldh);
        calculateDimensions();
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        //Bitmap bitmap = BitmapFactory.decodeResource(getContext().getResources(),R.drawable.alterralogo);
        int bitmapIndex = 0;
        ArrayList<Bitmap> list = new ArrayList<>();
        Bitmap bitmap = BitmapFactory.decodeFile(m_paths.get(0));

        for(int i = 0 ; i< nbPict;i++){
            list.add(BitmapFactory.decodeFile(m_paths.get(i))); //NOT OPTIMISED AT ALL, MAKE THE APP CRASH
        }

        for (int i = 0; i < numColumns; i++) {
            for (int j = 0; j < numRows; j++) {
                    resized = Bitmap.createScaledBitmap(list.get(bitmapIndex), cellSize, cellSize, true);
                    canvas.drawBitmap(resized, i* cellSize, j * cellSize, null);
                    bitmapIndex++;
            }
        }

    }

    @Override
    public boolean onTouchEvent(MotionEvent event) {
        mGestureDetector.onTouchEvent(event);
        mScaleGestureDetector.onTouchEvent(event);
        return true;
    }

    public class ZoomGesture extends GestureDetector.SimpleOnGestureListener {
        private boolean normal = true;

        @Override
        public boolean onDoubleTap(MotionEvent e) {
            return true;
        }
    }

    public class ScaleGesture extends ScaleGestureDetector.SimpleOnScaleGestureListener {
        @Override
        public boolean onScale(ScaleGestureDetector detector) {
            if(numColumns !=1){
                numColumns--;
                calculateDimensions();
            }
            invalidate();
            return true;
        }
    }
}

ScanPictures.java


public class ScanPictures {

    Context m_application_context;

    public ScanPictures(Context activity_context){
        m_application_context = activity_context;
    }

    public ArrayList<String> getImages(){

        ArrayList<String> paths = new ArrayList<String>(); //liste qui va contenir les chemins vers les images de la gallerie

        String[] columns = { MediaStore.Images.Media.DATA, MediaStore.Images.Media.BUCKET_DISPLAY_NAME };

        String selection = MediaStore.Images.Media.BUCKET_DISPLAY_NAME + " = ? ";

        String selectionArgs[] = {"Camera"};

        String orderBy = MediaStore.Images.Media.DATE_TAKEN;
        //Stores all the images from the gallery in Cursor
        Cursor cursor = m_application_context.getContentResolver().query(
                MediaStore.Images.Media.EXTERNAL_CONTENT_URI, columns, selection, selectionArgs, orderBy);

        //Total number of images
        int count = cursor.getCount();

        //Create an array to store path to all the images
        String[] arrPath = new String[count];

        for (int i = 0; i < count; i++) {
            cursor.moveToPosition(i);
            int dataColumnIndex = cursor.getColumnIndex(MediaStore.Images.Media.DATA);

            //Store the path of the image
            arrPath[i]= cursor.getString(dataColumnIndex);
            paths.add(arrPath[i]);

        }

        System.out.println(paths);

        return  paths;
    }
}

重现Android的图库

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