在 API 级别 19+ 的设备上，我们有 getByteCount() 和 getAllocationByteCount() ，每个都返回 Bitmap 的大小以字节为单位。后者考虑了 Bitmap 的事实。实际上可以表示比它的字节数更小的图像(例如，Bitmap 最初保存了一个更大的图像，但后来与 BitmapFactory.Options 和 inBitmap 一起使用来保存一个更小的图像)。

在大多数Android IPC场景中，尤其是那些涉及Parcelable的场景。 ，我们有一个 1MB 的“活页夹交易限制”。

用于确定是否给定 Bitmap对于 IPC 来说足够小，我们是否使用 getByteCount()或 getAllocationByteCount() ?

我的直觉告诉我们我们使用 getByteCount() ，因为这应该是 Bitmap 中当前图像的字节数正在接受，但我希望有人有更权威的答案。

最佳答案

写入包裹的图像数据大小为getByteCount()加上尺寸Bitmap的颜色表，如果有的话。还有大约 48 个字节的 Bitmap写入包裹的属性。以下代码分析和测试为这些陈述提供了基础。

native 函数写了Bitmap到 Parcel从 this file 的第 620 行开始.该函数包含在此处并添加了解释:

static jboolean Bitmap_writeToParcel(JNIEnv* env, jobject,
                                     jlong bitmapHandle,
                                     jboolean isMutable, jint density,
                                     jobject parcel) {
    const SkBitmap* bitmap = reinterpret_cast<SkBitmap*>(bitmapHandle);
    if (parcel == NULL) {
        SkDebugf("------- writeToParcel null parcel\n");
        return JNI_FALSE;
    }

    android::Parcel* p = android::parcelForJavaObject(env, parcel);

p->writeInt32(isMutable);
p->writeInt32(bitmap->colorType());
p->writeInt32(bitmap->alphaType());
p->writeInt32(bitmap->width());
p->writeInt32(bitmap->height());
p->writeInt32(bitmap->rowBytes());
p->writeInt32(density);

if (bitmap->colorType() == kIndex_8_SkColorType) {
    SkColorTable* ctable = bitmap->getColorTable();
    if (ctable != NULL) {
        int count = ctable->count();
        p->writeInt32(count);
        memcpy(p->writeInplace(count * sizeof(SkPMColor)),
               ctable->lockColors(), count * sizeof(SkPMColor));
        ctable->unlockColors();
    } else {
        p->writeInt32(0);   // indicate no ctable
    }
}

size_t size = bitmap->getSize();

android::Parcel::WritableBlob blob;
android::status_t status = p->writeBlob(size, &blob);
if (status) {
    doThrowRE(env, "Could not write bitmap to parcel blob.");
    return JNI_FALSE;
}

bitmap->lockPixels();
const void* pSrc =  bitmap->getPixels();
if (pSrc == NULL) {
    memset(blob.data(), 0, size);
} else {
    memcpy(blob.data(), pSrc, size);
}
bitmap->unlockPixels();

blob.release();
return JNI_TRUE;
}

size_t getSize() const { return fHeight * fRowBytes; }

int height() const { return fHeight; }

int rowBytes() const { return fRowBytes; }

p->writeInt32(bitmap->height());
p->writeInt32(bitmap->rowBytes());

byteCount=38400 allocatedByteCount=38400 parcelDataSize=38428
byteCount=7680 allocatedByteCount=38400 parcelDataSize=7708

    // Setup to get a mutable bitmap less than 40 Kbytes
    String path = "someSmallImage.jpg";
    Bitmap bm0 = BitmapFactory.decodeFile(path);
    // Need it mutable to change height
    Bitmap bm1 = bm0.copy(bm0.getConfig(), true);
    // Chop it to get a size less than 40K
    bm1.setHeight(bm1.getHeight() / 32);

    // Now we have a BitMap with size < 40K for the test
    Bitmap bm2 = bm1.copy(bm0.getConfig(), true);

    // What's the parcel size?
    Parcel p1 = Parcel.obtain();
    bm2.writeToParcel(p1, 0);

    // Expect byteCount and allocatedByteCount to be the same
    Log.i("Demo", String.format("byteCount=%d allocatedByteCount=%d parcelDataSize=%d",
            bm2.getByteCount(), bm2.getAllocationByteCount(), p1.dataSize()));

    // Resize to make byteCount and allocatedByteCount different
    bm2.setHeight(bm2.getHeight() / 4);

    // What's the parcel size?
    Parcel p2 = Parcel.obtain();
    bm2.writeToParcel(p2, 0);

    // Show that byteCount determines size of data written to parcel
    Log.i("Demo", String.format("byteCount=%d allocatedByteCount=%d parcelDataSize=%d",
            bm2.getByteCount(), bm2.getAllocationByteCount(), p2.dataSize()));

    p1.recycle();
    p2.recycle();

bc=12000000 abc=12000000 hgt=1500 wid=2000 rbyt=8000 dens=213

bc=744000 abc=12000000 hgt=93 wid=2000 rbyt=8000 dens=213

pds=48 mut=1 ctyp=4 atyp=1 hgt=93 wid=2000 rbyt=8000 dens=213

bitmap->getSize()= 744000 getByteCount()=744000

String path = "someImage.jpg";
Bitmap bm0 = BitmapFactory.decodeFile(path);
// Need it mutable to change height
Bitmap bm = bm0.copy(bm0.getConfig(), true);

// For reference, and to provide confidence that the parcel data dump is
// correct, log the bitmap attributes.
Log.i("Demo", String.format("bc=%d abc=%d hgt=%d wid=%d rbyt=%d dens=%d",
        bm.getByteCount(), bm.getAllocationByteCount(),
        bm.getHeight(), bm.getWidth(), bm.getRowBytes(), bm.getDensity()));
// Change size
bm.setHeight(bm.getHeight() / 16);
Log.i("Demo", String.format("bc=%d abc=%d hgt=%d wid=%d rbyt=%d dens=%d",
        bm.getByteCount(), bm.getAllocationByteCount(),
        bm.getHeight(), bm.getWidth(), bm.getRowBytes(), bm.getDensity()));

// Get a parcel and write the bitmap to it.
Parcel p = Parcel.obtain();
bm.writeToParcel(p, 0);

// When the image is too large to be written in-place,
// the parcel data size will be ~48 bytes (when there is no color map).
int parcelSize = p.dataSize();

// What are the first few ints in the parcel?
p.setDataPosition(0);
int mutable   = p.readInt(); //1
int colorType = p.readInt(); //2
int alphaType = p.readInt(); //3
int width     = p.readInt(); //4
int height    = p.readInt(); //5 bitmap->height()
int rowBytes  = p.readInt(); //6 bitmap->rowBytes()
int density   = p.readInt(); //7

Log.i("Demo", String.format("pds=%d mut=%d ctyp=%d atyp=%d hgt=%d wid=%d rbyt=%d dens=%d",
        parcelSize,  mutable, colorType, alphaType, height, width, rowBytes, density));

// From code analysis, we know that the value returned
// by SkBitmap::getSize() is the size of the image data written.
// We also know that the value of getSize() is height()*rowBytes().
// These are the values in ints 5 and 6.
int imageSize = height * rowBytes;

// Show that the size of image data stored is Bitmap.getByteCount()
Log.i("Demo", String.format("bitmap->getSize()= %d getByteCount()=%d", imageSize, bm.getByteCount()));

p.recycle();

关于android - 位图的 Parcelable 相关大小是多少？，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/31416191/