Android4.4 Uri获取图片及document理解
1. DocumentsContract.Document 定义
API文档声明：
Constants related to a document, including Cursor column names and flags.
严格意义上的document包含指针（或叫游标），纵列和标志。A document can be either an openable stream (with a specific MIME type), or a directory containing additional documents (with the MIME_TYPE_DIR MIME type). A directory represents the top of a subtree containing zero or more documents, which can recursively contain even more documents and directories.
一个document能是一个可以操作的流（是特殊MIME类型的）或者磁盘分支（包含可添加的documents<感觉有点难翻译，不好理解>）. 一个磁盘分支代表包含0个或多个document的树的顶端，能够包含更多的磁盘分支或document.(似乎是树的存储概念，数据结构-树)。All columns are read-only to client applications.
所有的纵列只能被客户端程序所读取。
2. Android4.4 Uri
这里先看下4.4之前的uri的形式：
Uri ： content://media/extenral/images/media/17766
再看4.4及以后的Uri形式：
content://com.android.providers.media.documents/document/image%3A82482
两者是不同的，4.4以上的系统使用了document封装过了。
查看API可以找到关于操作document的类：
类 DocumentsContract
API文档说明：
Defines the contract between a documents provider and the platform.
定义用于连接document provider和平台。To create a document provider, extend DocumentsProvider, which provides a foundational implementation of this contract.
All client apps must hold a valid URI permission grant to access documents, typically issued when a user makes a selection through ACTION_OPEN_DOCUMENT, ACTION_CREATE_DOCUMENT, or ACTION_OPEN_DOCUMENT_TREE.
详见Java.lang.Object
↳ android.provider.DocumentsContract
该类提供许多关于操作document的方法。
3. 获取图片代码分析document
获取图片代码
private void handleImageOkKitKat(Intent data) {
String imagePath=null;
Uri uri = data.getData();
Log.d("intent.getData :",""+uri);
if (DocumentsContract.isDocumentUri(this,uri)){
String docId = DocumentsContract.getDocumentId(uri);
Log.d("getDocumentId(uri) :",""+docId);
Log.d("uri.getAuthority() :",""+uri.getAuthority());
if ("com.android.providers.media.documents".equals(uri.getAuthority())){
String id = docId.split(":")[1];
String selection = MediaStore.Images.Media._ID + "=" + id;
imagePath = getImagePath(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,selection);
}
else if ("com.android,providers.downloads.documents".equals(uri.getAuthority())) {
Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"),Long.valueOf(docId));
imagePath = getImagePath(contentUri,null);
}
}
else if ("content".equalsIgnoreCase(uri.getScheme())){
imagePath = getImagePath(uri,null);
}
displayImage(imagePath);
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4.4以上系统获得的Uri内容：
Uri uri = data.getData();
Log.d("uri=intent.getData :",""+uri);- 1
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运行结果：D/uri=intent.getData :﹕ content://com.android.providers.media.documents/document/image%3A82483
可以看到Uri不同于之前系统版本，选取不同的图片观察Uri是相同的。
-
判断该Uri是否是document封装过的
静态方法：isDocumentUri(Context context, Uri uri)
DocumentsContract.isDocumentUri(this,uri); -
获取图片数据库数据表里指定的行getDocumentId(Uri uri)
静态方法：getDocumentId(Uri uri)
DocumentsContract.getDocumentId(uri);
Log.d("getDocumentId(uri) :",""+docId);- 1
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运行结果：
D/getDocumentId(uri) :﹕ image:82482
返回一个字符串，实际上就代表了该图片存储数据库数据表里的行的位置。
- 获取Uri的路径 getAuthority()
属于Uri对象的对象方法。
uri.getAuthority();
Log.d("uri.getAuthority() :",""+uri.getAuthority());- 1
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运行结果：
D/uri.getAuthority() :﹕ com.android.providers.media.documents
可以对照Uri的组成判断。
“content://” + 数据的路径 + 标示ID(可选)
如果路径不同获取图片是不一样的：
代码：
if ("com.android.providers.media.documents".equals(uri.getAuthority())){
String id = docId.split(":")[1];
String selection = MediaStore.Images.Media._ID + "=" + id;
imagePath = getImagePath(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,selection);
}
else if ("com.android.providers.downloads.documents".equals(uri.getAuthority())) {
Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"),Long.valueOf(docId));
imagePath = getImagePath(contentUri,null);
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个人理解是com.android.providers.media.documents路径下的图片是经过特殊封装的，而com.android.providers.downloads.documents并没有，这里再观察获取图片完整路径的方法的代码：
public String getImagePath(Uri uri,String selection) {
String path = null;
Cursor cursor = getContentResolver().query(uri,null,selection,null,null); //内容提供器
if (cursor!=null){
if (cursor.moveToFirst()){
path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA)); //获取路径
}
}
cursor.close();
return path;
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本质是使用内容提供器获取数据。
观察com.android.providers.media.documents路径和com.android.providers.downloads.documents获取完整路径的代码
可以知道com.android.providers.media.documents使用document封装是向数据表添加了MediaStore.Images.Media.DATA列形成了一个新数据库
MediaStore.Images.Media.EXTERNAL_CONTENT_URI只有根据MediaStore.Images.Media.DATA来查询，此时的id（id指的不是之前的getDocumentId(uri)的docID,而是将docID以：分割获取的数值标号）是对应图片行MediaStore.Images.Media.DATA列的标号。
而com.android.providers.downloads.documents路径则是以4.4之前版本的形式的Uri存储的。
docID: image:82482
id: 82482
以’:’分割字符串，获取id
Android4.4 之前获取图片路径
private void handleImageBeforeKitKat(Intent data) {
Uri uri = data.getData();
String imagePath = getImagePath(uri,null);
displayImage(imagePath);
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Uri里就包含了该图片所在行的id。
Uri ： content://media/extenral/images/media/17766
使用内容提供器可以轻松获取路径。
4. DEMO 主要代码
public class MainActivity extends AppCompatActivity {
private static final int TAKE_PHOTO = 1;
private static final int CROP_PHOTO = 2;
private static final int CHOOSE_PIC = 3;
private Button takePhoto;
private Button choosePicture;
private ImageView picture;
Uri imageUri;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
picture = (ImageView) findViewById(R.id.picture);
takePhoto = (Button) findViewById(R.id.take_photo);
takePhoto.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
File outputFile = new File(Environment.getExternalStorageDirectory(),"output_image.jpg");
try{
if (outputFile.exists()){
outputFile.delete();
}
outputFile.createNewFile();
} catch (IOException e) {
e.printStackTrace();
}
imageUri = Uri.fromFile(outputFile);
Intent intent = new Intent("android.media.action.IMAGE_CAPTURE");
intent.putExtra(MediaStore.EXTRA_OUTPUT,imageUri);
startActivityForResult(intent,TAKE_PHOTO);
}
});
choosePicture = (Button) findViewById(R.id.choose_picture);
choosePicture.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
Intent intent = new Intent("android.intent.action.GET_CONTENT");
intent.setType("image/*");
startActivityForResult(intent,CHOOSE_PIC);
}
});
}
@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data){
switch (requestCode){
case TAKE_PHOTO:
if (resultCode==RESULT_OK){
Intent intent = new Intent("com.android.camera.action.CROP");
intent.setDataAndType(imageUri,"image/*");
intent.putExtra("scale", true);
intent.putExtra(MediaStore.EXTRA_OUTPUT,imageUri);
startActivityForResult(intent,CROP_PHOTO);
}
break;
case CROP_PHOTO:
if (resultCode==RESULT_OK){
try {
Bitmap bitmap = BitmapFactory.decodeStream(getContentResolver().openInputStream(imageUri));
picture.setImageBitmap(bitmap);
} catch (FileNotFoundException e) {
e.printStackTrace();
}
}
break;
case CHOOSE_PIC:
if (resultCode==RESULT_OK){
if (Build.VERSION.SDK_INT>=19){
handleImageOkKitKat(data);
}
else{
handleImageBeforeKitKat(data);
}
}
default:
break;
}
}
private void handleImageBeforeKitKat(Intent data) {
Uri uri = data.getData();
String imagePath = getImagePath(uri,null);
displayImage(imagePath);
}
private void handleImageOkKitKat(Intent data) {
String imagePath=null;
Uri uri = data.getData();
Log.d("uri=intent.getData :",""+uri);
if (DocumentsContract.isDocumentUri(this,uri)){
String docId = DocumentsContract.getDocumentId(uri); //数据表里指定的行
Log.d("getDocumentId(uri) :",""+docId);
Log.d("uri.getAuthority() :",""+uri.getAuthority());
if ("com.android.providers.media.documents".equals(uri.getAuthority())){
String id = docId.split(":")[1];
String selection = MediaStore.Images.Media._ID + "=" + id;
imagePath = getImagePath(MediaStore.Images.Media.EXTERNAL_CONTENT_URI,selection);
}
else if ("com.android.providers.downloads.documents".equals(uri.getAuthority())) {
Uri contentUri = ContentUris.withAppendedId(Uri.parse("content://downloads/public_downloads"),Long.valueOf(docId));
imagePath = getImagePath(contentUri,null);
}
}
else if ("content".equalsIgnoreCase(uri.getScheme())){
imagePath = getImagePath(uri,null);
}
displayImage(imagePath);
}
private void displayImage(String imagePath) {
if (imagePath!=null){
Bitmap bitImage = BitmapFactory.decodeFile(imagePath);
picture.setImageBitmap(bitImage);
}
else{
Toast.makeText(MainActivity.this,"failed to get image",Toast.LENGTH_SHORT).show();
}
}
public String getImagePath(Uri uri,String selection) {
String path = null;
Cursor cursor = getContentResolver().query(uri,null,selection,null,null); //内容提供器
if (cursor!=null){
if (cursor.moveToFirst()){
path = cursor.getString(cursor.getColumnIndex(MediaStore.Images.Media.DATA)); //获取路径
}
}
cursor.close();
return path;
}
}
原文http://blog.csdn.net/svizzera/article/details/50705195上一篇： CI框架数据库查询之join用法分析
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