Taking Photos Simply

#Taking Photos Simply笔记 以下内容均是使用已经存在的carmera app进行拍照。 ##Request Camera Permission 如果拍照是你的app一个非常重要的功能，在manifest文件使用<uses-feature>标签，Google Play只会对有相机的设备可见。

<manifest ... > <uses-feature android:name="android.hardware.camera" android:required="true" /> ... </manifest>

也可以在运行时调用hasSystemFeature(PackageManger.FEATURE_CAMERA)方法来检查相机是否可用。

##Take a Phote with the Camera App 调用camera app过程有三部分工作：实例化Intent对象、开启外部Activity、处理图片结果。 使用Intent开启拍照功能示例:

static final int REQUEST_IMAGE_CAPTURE = 1; private void dispatchTakePictureIntent() { Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE); if (takePictureIntent.resolveActivity(getPackageManager()) != null) { startActivityForResult(takePictureIntent, REQUEST_IMAGE_CAPTURE); } }

##Get the Thumbnail Android Camera app 返回的Intent，key为"data"，value为拍摄图片的缩略图。 代码示例如下:

@Override protected void onActivityResult(int requestCode, int resultCode, Intent data) { if (requestCode == REQUEST_IMAGE_CAPTURE && resultCode == RESULT_OK) { Bundle extras = data.getExtras(); Bitmap imageBitmap = (Bitmap) extras.get("data"); mImageView.setImageBitmap(imageBitmap); } }

##Save the Full-size Photo 如果指定一个文件Android Camera app会保存全尺寸图片。 getExternalStoragepublicDirectory(Environment.DIRECTORY_PICTURE)返回的目录是存放可分享照片的合适地方。需要外部存储的写权限:

<manifest ...> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" /> ... </manifest>

如果想照片只能你的app使用，可以存放在getExternalFilesDir()返回的目录。Android 4.4和之后版本写这个目录不需要WRITE_EXTERNAL_STORAGE权限。权限声明可以添加maxSdkVersion来指定需要权限的最大版本:

<manifest ...> <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" android:maxSdkVersion="18" /> ... </manifest>

确定好文件目录，创建用时间戳命名的文件:

String mCurrentPhotoPath; private File createImageFile() throws IOException { // Create an image file name String timeStamp = new SimpleDateFormat("yyyyMMdd_HHmmss").format(new Date()); String imageFileName = "JPEG_" + timeStamp + "_"; File storageDir = getExternalFilesDir(Environment.DIRECTORY_PICTURES); File image = File.createTempFile( imageFileName, /* prefix */ ".jpg", /* suffix */ storageDir /* directory */ ); // Save a file: path for use with ACTION_VIEW intents mCurrentPhotoPath = image.getAbsolutePath(); return image; }

为相片创建好文件后，开始创建Intent:

static final int REQUEST_TAKE_PHOTO = 1; private void dispatchTakePictureIntent() { Intent takePictureIntent = new Intent(MediaStore.ACTION_IMAGE_CAPTURE); // Ensure that there's a camera activity to handle the intent if (takePictureIntent.resolveActivity(getPackageManager()) != null) { // Create the File where the photo should go File photoFile = null; try { photoFile = createImageFile(); } catch (IOException ex) { // Error occurred while creating the File ... } // Continue only if the File was successfully created if (photoFile != null) { Uri photoURI = FileProvider.getUriForFile(this, "com.example.android.fileprovider",photoFile); takePictureIntent.putExtra(MediaStore.EXTRA_OUTPUT, photoURI); startActivityForResult(takePictureIntent, REQUEST_TAKE_PHOTO); } } }

注意:getUriForFile(Context,String,File)返回content://URI。app target是Android 7.0(API level 24)或更高，跨包传递file://URI会抛出FileUriExposedException。在低版本系统中（测试HTC 4.4.3）使用content:// URI不能保存拍照图片。

在manifest文件配置FileProvider:

<application> ... <provider android:name="android.support.v4.content.FileProvider" android:authorities="com.example.android.fileprovider" android:exported="false" android:grantUriPermissions="true"> <meta-data android:name="android.support.FILE_PROVIDER_PATHS" android:resource="@xml/file_paths"></meta-data> </provider> ... </application>

res/xml/file_path.xml配置可选的文件路径：

<?xml version="1.0" encoding="utf-8"?> <paths xmlns:android="http://schemas.android.com/apk/res/android"> <external-path name="my_images" path="Android/data/com.example.package.name/files/Pictures" /> </paths>

##Add the Photo to a Gallery

注意：如果照片保存在getExternalFilesDir()返回的目录下，media scanner不能访问文件，因为在你的app私有目录下。

添加你的照到Media Provider’s database:

private void galleryAddPic() { Intent mediaScanIntent = new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE); File f = new File(mCurrentPhotoPath); Uri contentUri = Uri.fromFile(f); mediaScanIntent.setData(contentUri); this.sendBroadcast(mediaScanIntent); }

如果照片在你的app私有目录下，上面代码没有任何作用，使用FileProvider生成URI依然如此。例如：

Intent intent=new Intent(Intent.ACTION_MEDIA_SCANNER_SCAN_FILE); String filePath=Environment.getExternalStorageDirectory()+"/Android/data/com.addcn.car8891/files/84481_20130116142820494200_1.jpg"; File file=new File(filePath); Uri uri=Uri.fromFile(file); intent.setData(uri); sendBroadcast(intent);

##Decode a Scaled Image 显示全尺寸的图片很容易内存溢出，使用适应目标View大小的图片可以极大减少内存：

private void setPic() { // Get the dimensions of the View int targetW = mImageView.getWidth(); int targetH = mImageView.getHeight(); // Get the dimensions of the bitmap BitmapFactory.Options bmOptions = new BitmapFactory.Options(); bmOptions.inJustDecodeBounds = true; BitmapFactory.decodeFile(mCurrentPhotoPath, bmOptions); int photoW = bmOptions.outWidth; int photoH = bmOptions.outHeight; // Determine how much to scale down the image int scaleFactor = Math.min(photoW/targetW, photoH/targetH); // Decode the image file into a Bitmap sized to fill the View bmOptions.inJustDecodeBounds = false; //inSampleSize取样数，表示inSampleSize个像素取一个像素 bmOptions.inSampleSize = scaleFactor; bmOptions.inPurgeable = true; Bitmap bitmap = BitmapFactory.decodeFile(mCurrentPhotoPath, bmOptions); mImageView.setImageBitmap(bitmap); }