android - Android：位图处置

Question

我在处理位图时遇到问题：

请检查以下代码：

public class MainActivity extends Activity implements OnClickListener {

ImageView imageView1;
Bitmap s;

@Override
protected void onCreate(Bundle savedInstanceState) {
    requestWindowFeature(Window.FEATURE_NO_TITLE);
    // logHeap("ECAonCreate");

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    imageView1 = (ImageView) findViewById(R.id.imageView1);
    s = decodeFil3e(R.drawable.launchimage20481496);
        ImageButton btn =(ImageButton) findViewById(R.id.btnEnter);
    btn.setOnClickListener(this);
}

public int calculateInSampleSize(BitmapFactory.Options options,
        int reqWidth, int reqHeight) {
    // Raw height and width of image
    final int height = options.outHeight;
    final int width = options.outWidth;
    int inSampleSize = 1;

    if (height > reqHeight || width > reqWidth) {

        // Calculate ratios of height and width to requested height and
        // width
        final int heightRatio = Math.round((float) height
                / (float) reqHeight);
        final int widthRatio = Math.round((float) width / (float) reqWidth);
        inSampleSize = heightRatio < widthRatio ? heightRatio : widthRatio;
    }

    return inSampleSize;
}

private Bitmap decodeFil3e(int f) {
    // Decode image size
    BitmapFactory.Options o = new BitmapFactory.Options();
    o.inJustDecodeBounds = true;
    o.inTempStorage = new byte[16 * 1024];

    BitmapFactory.decodeResource(getResources(), f, o);

    Display display = getWindowManager().getDefaultDisplay();
    int width = display.getWidth();
    int height = display.getHeight();
    int[] resized = ImageSize(new int[] { o.outWidth, o.outHeight }, width,
            height);

    BitmapFactory.Options o2 = new BitmapFactory.Options();
    o2.inSampleSize = calculateInSampleSize(o2, resized[0], resized[1]);
    o2.inTempStorage = new byte[16 * 1024];
    o = null;
    o2 = null;

    return BitmapFactory.decodeResource(getResources(), f, o2);

}

public static int[] ImageSize(int[] imgSize, int maxWidth, int maxHeight) {
    int[] size = new int[2];
    try {
        for (double i = 1; i <= 20; i += 0.1) {
            double height = imgSize[1] / i;
            double width = imgSize[0] / i;
            if (height < maxHeight && width < maxWidth) {
                size[0] = (int) width;
                size[1] = (int) height;
                return size;
            }
        }
        return imgSize;
    } catch (Exception ex) {
        return size;

    }
}

public static void logHeap(String functionname) {
    Double allocated = new Double(Debug.getNativeHeapAllocatedSize())
            / new Double((1048576));
    Double available = new Double(Debug.getNativeHeapSize()) / 1048576.0;
    Double free = new Double(Debug.getNativeHeapFreeSize()) / 1048576.0;
    DecimalFormat df = new DecimalFormat();
    df.setMaximumFractionDigits(2);
    df.setMinimumFractionDigits(2);

    Log.d("tag", "debug. =================================");
    Log.d("tag", "debug.heap native: allocated " + df.format(allocated)
            + "MB of " + df.format(available) + "MB (" + df.format(free)
            + "MB free)");
    Log.d("tag",
            "functionname:"
                    + functionname
                    + ":debug.memory: allocated: "
                    + df.format(new Double(Runtime.getRuntime()
                            .totalMemory() / 1048576))
                    + "MB of "
                    + df.format(new Double(
                            Runtime.getRuntime().maxMemory() / 1048576))
                    + "MB ("
                    + df.format(new Double(Runtime.getRuntime()
                            .freeMemory() / 1048576)) + "MB free)");
}

@Override
protected void onDestroy() {
    super.onDestroy();
    if (s != null) {
        s.recycle();
        s = null;
    }

    if (imageView1 != null) {
        if (((BitmapDrawable) imageView1.getDrawable()) != null) {
            ((BitmapDrawable) imageView1.getDrawable()).getBitmap()
                    .recycle();
        }

        imageView1.setBackground(null);
        imageView1.setBackgroundDrawable(null);
        imageView1.setImageBitmap(null);
        imageView1 = null;
    }

    System.gc();
    logHeap("ECAonDestroy");
}

@Override
protected void onResume() {
    super.onResume();
    logHeap("ECAonResume");
};

public void onClick(View v) {

    Intent a = new Intent(this, Activity2.class);
    startActivity(a);
    finish();

}
}

logHeap 函数会显示当前占用的堆内存。

问题是即使将位图实例设置为 null.heap 大小也不会减小。