我正在研究从web服务器下载图像的功能,在屏幕上显示它,如果用户希望保持图像,将其保存在SD卡的某个文件夹中。有没有一种简单的方法来获取位图并将其保存到我选择的SD卡文件夹中?

我的问题是,我可以下载图像,在屏幕上显示为位图。我能够找到的将图像保存到特定文件夹的唯一方法是使用FileOutputStream,但这需要一个字节数组。我不知道如何转换(如果这是正确的方式)从位图到字节数组,所以我可以使用FileOutputStream写入数据。

我的另一个选择是使用MediaStore:

MediaStore.Images.Media.insertImage(getContentResolver(), bm,
    barcodeNumber + ".jpg Card Image", barcodeNumber + ".jpg Card Image");

它可以很好地保存到SD卡,但不允许您自定义文件夹。


当前回答

您应该使用Bitmap.compress()方法将位图保存为文件。它将压缩(如果所使用的格式允许的话)您的图片并将其推入OutputStream。

下面是一个通过getImageBitmap(myurl)获得的位图实例,可以压缩为JPEG,压缩率为85%:

// Assume block needs to be inside a Try/Catch block.
String path = Environment.getExternalStorageDirectory().toString();
OutputStream fOut = null;
Integer counter = 0;
File file = new File(path, "FitnessGirl"+counter+".jpg"); // the File to save , append increasing numeric counter to prevent files from getting overwritten.
fOut = new FileOutputStream(file);

Bitmap pictureBitmap = getImageBitmap(myurl); // obtaining the Bitmap
pictureBitmap.compress(Bitmap.CompressFormat.JPEG, 85, fOut); // saving the Bitmap to a file compressed as a JPEG with 85% compression rate
fOut.flush(); // Not really required
fOut.close(); // do not forget to close the stream

MediaStore.Images.Media.insertImage(getContentResolver(),file.getAbsolutePath(),file.getName(),file.getName());

其他回答

我知道这个问题很老了,但是现在我们可以在没有WRITE_EXTERNAL_STORAGE权限的情况下实现相同的结果。而不是我们可以使用文件提供程序。

private fun storeBitmap(bitmap: Bitmap, file: File){
        requireContext().getUriForFile(file)?.run {
            requireContext().contentResolver.openOutputStream(this)?.run {
                bitmap.compress(Bitmap.CompressFormat.JPEG, 100, this)
                close()
            }
        }
    }

如何从提供者检索文件?

fun Context.getUriForFile(file: File): Uri? {
        return FileProvider.getUriForFile(
            this,
            "$packageName.fileprovider",
            file
        )
    }

另外,不要忘记在Android manifest中注册你的提供商

<provider
        android:name="androidx.core.content.FileProvider"
        android:authorities="${applicationId}.fileprovider"
        android:exported="false"
        android:grantUriPermissions="true">
        <meta-data
            android:name="android.support.FILE_PROVIDER_PATHS"
            android:resource="@xml/file_paths"/>
    </provider>

我还想保存一张图片。但是我的问题(?)是我想从我画的位图中保存它。

我是这样写的:

 @Override
 public boolean onOptionsItemSelected(MenuItem item) {
            switch (item.getItemId()) {
            case R.id.save_sign:      

                myView.save();
                break;

            }
            return false;    

    }

public void save() {
            String filename;
            Date date = new Date(0);
            SimpleDateFormat sdf = new SimpleDateFormat ("yyyyMMddHHmmss");
            filename =  sdf.format(date);

            try{
                 String path = Environment.getExternalStorageDirectory().toString();
                 OutputStream fOut = null;
                 File file = new File(path, "/DCIM/Signatures/"+filename+".jpg");
                 fOut = new FileOutputStream(file);

                 mBitmap.compress(Bitmap.CompressFormat.JPEG, 85, fOut);
                 fOut.flush();
                 fOut.close();

                 MediaStore.Images.Media.insertImage(getContentResolver()
                 ,file.getAbsolutePath(),file.getName(),file.getName());

            }catch (Exception e) {
                e.printStackTrace();
            }

 }
Bitmap bbicon;

bbicon=BitmapFactory.decodeResource(getResources(),R.drawable.bannerd10);
//ByteArrayOutputStream baosicon = new ByteArrayOutputStream();
//bbicon.compress(Bitmap.CompressFormat.PNG,0, baosicon);
//bicon=baosicon.toByteArray();

String extStorageDirectory = Environment.getExternalStorageDirectory().toString();
OutputStream outStream = null;
File file = new File(extStorageDirectory, "er.PNG");
try {
    outStream = new FileOutputStream(file);
    bbicon.compress(Bitmap.CompressFormat.PNG, 100, outStream);
    outStream.flush();
    outStream.close();
} catch(Exception e) {

}

您应该使用Bitmap.compress()方法将位图保存为文件。它将压缩(如果所使用的格式允许的话)您的图片并将其推入OutputStream。

下面是一个通过getImageBitmap(myurl)获得的位图实例,可以压缩为JPEG,压缩率为85%:

// Assume block needs to be inside a Try/Catch block.
String path = Environment.getExternalStorageDirectory().toString();
OutputStream fOut = null;
Integer counter = 0;
File file = new File(path, "FitnessGirl"+counter+".jpg"); // the File to save , append increasing numeric counter to prevent files from getting overwritten.
fOut = new FileOutputStream(file);

Bitmap pictureBitmap = getImageBitmap(myurl); // obtaining the Bitmap
pictureBitmap.compress(Bitmap.CompressFormat.JPEG, 85, fOut); // saving the Bitmap to a file compressed as a JPEG with 85% compression rate
fOut.flush(); // Not really required
fOut.close(); // do not forget to close the stream

MediaStore.Images.Media.insertImage(getContentResolver(),file.getAbsolutePath(),file.getName(),file.getName());
try (FileOutputStream out = new FileOutputStream(filename)) {
    bmp.compress(Bitmap.CompressFormat.PNG, 100, out); // bmp is your Bitmap instance
    // PNG is a lossless format, the compression factor (100) is ignored
} catch (IOException e) {
    e.printStackTrace();
}