java - Android如何在加载新图像之前回收图像

Question

我遇到内存不足的问题，其中显示了全屏图像。我想全屏显示图像，并且有两个按钮可以向左或向右循环显示图像。如何在显示下一个图像之前回收过去的图像以防止内存不足异常？或者有更好的方法吗？

这是我在其中查看图像的类(class)。

public class ImageViewActivity extends Activity
{
private Button btnHome;
private Button btnBack;
private ImageButton btnLeft;
private ImageButton btnRight;
ImageView imageView;
RelativeLayout layout;

int height;
int width;

Bitmap bitmap;
String[] imagesPath;
int position;

// These matrices will be used to move and zoom image
Matrix matrix = new Matrix();
Matrix savedMatrix = new Matrix();

// We can be in one of these 3 states
static final int NONE = 0;
static final int DRAG = 1;
static final int ZOOM = 2;
int mode = NONE;

// Remember some things for zooming
PointF start = new PointF();
PointF mid = new PointF();
float oldDist = 1f;
String savedItemClicked;

@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.imageview_activity);

    btnHome = (Button) findViewById(R.id.btnHome);
    btnBack = (Button) findViewById(R.id.btnBack);
    btnLeft = (ImageButton) findViewById(R.id.leftArrow);
    btnRight = (ImageButton) findViewById(R.id.rightArrow);

    DisplayMetrics displayMetrics = new DisplayMetrics();
    getWindowManager().getDefaultDisplay().getMetrics(displayMetrics);
    height = displayMetrics.heightPixels;
    width = displayMetrics.widthPixels;

    imagesPath = getIntent().getStringExtra("IMAGES").split("\\|");
    position = getIntent().getIntExtra("POSITION", 0);

    bitmap = BitmapFactory.decodeFile(imagesPath[position]);

    imageView = (ImageView)findViewById(R.id.displayImage);
    imageView.setImageBitmap(Bitmap.createScaledBitmap(bitmap, width, height, false));

    btnLeft.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View arg0)
        {
            if (position == 0)
                position = 5;
            else
                position--;

            RectF imageRectF = new RectF(0, 0, width, height);
            RectF viewRectF = new RectF(0, 0, width, height);
            matrix.setRectToRect(imageRectF, viewRectF, Matrix.ScaleToFit.CENTER);

            bitmap = BitmapFactory.decodeFile(imagesPath[position]);
            ImageView imageView = (ImageView)findViewById(R.id.displayImage);
            imageView.setImageBitmap(Bitmap.createScaledBitmap(bitmap, width, height, false));

            imageView.setImageMatrix(matrix);
        }
    });

    btnRight.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View arg0)
        {
            if (position == 5)
                position = 0;
            else
                position++;

            RectF imageRectF = new RectF(0, 0, width, height);
            RectF viewRectF = new RectF(0, 0, width, height);
            matrix.setRectToRect(imageRectF, viewRectF, Matrix.ScaleToFit.CENTER);

            bitmap = BitmapFactory.decodeFile(imagesPath[position]);
            ImageView imageView = (ImageView)findViewById(R.id.displayImage);
            imageView.setImageBitmap(Bitmap.createScaledBitmap(bitmap, width, height, false));

            imageView.setImageMatrix(matrix);
        }
    });

    btnHome.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View arg0)
        {
            Intent ActivitySwitch = new Intent(getApplicationContext(), MainMenuActivity.class);
            startActivity(ActivitySwitch);
        }
    });

    btnBack.setOnClickListener(new View.OnClickListener()
    {
        public void onClick(View arg0)
        {
            Intent ActivitySwitch = new Intent(getApplicationContext(), AddClientActivity.class);
            startActivity(ActivitySwitch);
        }
    });

    imageView.setOnTouchListener(new View.OnTouchListener()
    {
        @Override
        public boolean onTouch(View v, MotionEvent event)
        {
            ImageView view = (ImageView) v;
            dumpEvent(event);

            // Handle touch events here...
            switch (event.getAction() & MotionEvent.ACTION_MASK) {
                case MotionEvent.ACTION_DOWN:
                    savedMatrix.set(matrix);
                    start.set(event.getX(), event.getY());
                    mode = DRAG;
                    break;
                case MotionEvent.ACTION_POINTER_DOWN:
                    oldDist = spacing(event);
                    if (oldDist > 10f) {
                        savedMatrix.set(matrix);
                        midPoint(mid, event);
                        mode = ZOOM;
                    }
                    break;
                case MotionEvent.ACTION_UP:
                case MotionEvent.ACTION_POINTER_UP:
                    mode = NONE;
                    break;
                case MotionEvent.ACTION_MOVE:
                    if (mode == DRAG) {
                        // ...
                        matrix.set(savedMatrix);
                        matrix.postTranslate(event.getX() - start.x, event.getY()
                                - start.y);
                    } else if (mode == ZOOM) {
                        float newDist = spacing(event);
                        if (newDist > 10f) {
                            matrix.set(savedMatrix);
                            float scale = newDist / oldDist;
                            matrix.postScale(scale, scale, mid.x, mid.y);
                        }
                    }
                    break;
            }

            view.setImageMatrix(matrix);
            return true;
        }
    });

}

private void dumpEvent(MotionEvent event) {
    String names[] = { "DOWN", "UP", "MOVE", "CANCEL", "OUTSIDE",
            "POINTER_DOWN", "POINTER_UP", "7?", "8?", "9?" };
    StringBuilder sb = new StringBuilder();
    int action = event.getAction();
    int actionCode = action & MotionEvent.ACTION_MASK;
    sb.append("event ACTION_").append(names[actionCode]);
    if (actionCode == MotionEvent.ACTION_POINTER_DOWN
            || actionCode == MotionEvent.ACTION_POINTER_UP) {
        sb.append("(pid ").append(
                action >> MotionEvent.ACTION_POINTER_ID_SHIFT);
        sb.append(")");
    }
    sb.append("[");
    for (int i = 0; i < event.getPointerCount(); i++) {
        sb.append("#").append(i);
        sb.append("(pid ").append(event.getPointerId(i));
        sb.append(")=").append((int) event.getX(i));
        sb.append(",").append((int) event.getY(i));
        if (i + 1 < event.getPointerCount())
            sb.append(";");
    }
    sb.append("]");
}

/** Determine the space between the first two fingers */
private float spacing(MotionEvent event) {
    float x = event.getX(0) - event.getX(1);
    float y = event.getY(0) - event.getY(1);
    return (float)Math.sqrt(x * x + y * y);
}

/** Calculate the mid point of the first two fingers */
private void midPoint(PointF point, MotionEvent event) {
    float x = event.getX(0) + event.getX(1);
    float y = event.getY(0) + event.getY(1);
    point.set(x / 2, y / 2);
}

感谢您的任何意见，如果您需要任何其他信息，请随时询问!

Answer 1

我要么缩小图像，要么考虑使用 Picasso 图像加载库:http://square.github.io/picasso/

它的使用也非常简单，并且可以防止很多内存不足异常。

Picasso.with(context).load("http://i.imgur.com/DvpvklR.png").into(imageView);