我正在我的应用程序中添加一些样本项目，以便当用户第一次查看它时，它不会显得太空洞。样本项目列表应该有一个图像，我要使用的图像已经存储在应用程序的/res/drawable文件夹中。
由于我已经有一个从URI加载项目图像的方法，所以我想获取到/res/drawable/myImage.jpg的URI，但我似乎做不对。
流程如下： 创建项，其中包含表示图像URI的字符串。 将项目列表发送到List 该列表通过将字符串转换为URL并运行url.openStream()来在后台任务中加载图像。
我已经尝试了几个选项来获取URI，但没有成功。 "android.resource://....."说未知协议 "file://"文件找不到
所以现在我有点迷失如何解决这个问题..
你应该使用ContentResolver来打开资源URI：
Uri uri = Uri.parse("android.resource://your.package.here/drawable/image_name");
InputStream stream = getContentResolver().openInputStream(uri);
你也可以使用这种方法打开文件和内容URI。
/**
* get uri to drawable or any other resource type if u wish
* @param context - context
* @param drawableId - drawable res id
* @return - uri
*/
public static final Uri getUriToDrawable(@NonNull Context context,
@AnyRes int drawableId) {
Uri imageUri = Uri.parse(ContentResolver.SCHEME_ANDROID_RESOURCE
+ "://" + context.getResources().getResourcePackageName(drawableId)
+ '/' + context.getResources().getResourceTypeName(drawableId)
+ '/' + context.getResources().getResourceEntryName(drawableId) );
return imageUri;
}
基于上述内容 - 适用于任何资源的微调版本：
/**
* get uri to any resource type Via Context Resource instance
* @param context - context
* @param resId - resource id
* @throws Resources.NotFoundException if the given ID does not exist.
* @return - Uri to resource by given id
*/
public static final Uri getUriToResource(@NonNull Context context,
@AnyRes int resId)
throws Resources.NotFoundException {
/** Return a Resources instance for your application's package. */
Resources res = context.getResources();
Uri resUri = getUriToResource(res,resId);
return resUri;
}
/**
* get uri to any resource type via given Resource Instance
* @param res - resources instance
* @param resId - resource id
* @throws Resources.NotFoundException if the given ID does not exist.
* @return - Uri to resource by given id
*/
public static final Uri getUriToResource(@NonNull Resources res,
@AnyRes int resId)
throws Resources.NotFoundException {
/**
* Creates a Uri which parses the given encoded URI string.
* @param uriString an RFC 2396-compliant, encoded URI
* @throws NullPointerException if uriString is null
* @return Uri for this given uri string
*/
Uri resUri = Uri.parse(ContentResolver.SCHEME_ANDROID_RESOURCE +
"://" + res.getResourcePackageName(resId)
+ '/' + res.getResourceTypeName(resId)
+ '/' + res.getResourceEntryName(resId));
/** return uri */
return resUri;
}
一些信息：
From the Java Language spec.:
"17.5 Final Field Semantics
... when the object is seen by another thread, that thread will always
see the correctly constructed version of that object's final fields.
It will also see versions of any object or array referenced by
those final fields that are at least as up-to-date as the final fields
are."
In that same vein, all non-transient fields within Uri
implementations should be final and immutable so as to ensure true
immutability for clients even when they don't use proper concurrency
control.
For reference, from RFC 2396:
"4.3. Parsing a URI Reference
A URI reference is typically parsed according to the four main
components and fragment identifier in order to determine what
components are present and whether the reference is relative or
absolute. The individual components are then parsed for their
subparts and, if not opaque, to verify their validity.
Although the BNF defines what is allowed in each component, it is
ambiguous in terms of differentiating between an authority component
and a path component that begins with two slash characters. The
greedy algorithm is used for disambiguation: the left-most matching
rule soaks up as much of the URI reference string as it is capable of
matching. In other words, the authority component wins."
...
3. URI Syntactic Components
The URI syntax is dependent upon the scheme.
In general, absolute URI are written as follows:
<scheme>:<scheme-specific-part>
An absolute URI contains the name of the scheme being used (<scheme>)
followed by a colon (":") and then a string (the <scheme-specific-part>)
whose interpretation depends on the scheme.
The URI syntax does not require that the scheme-specific-part have any
general structure or set of semantics which is common among all URI.
However, a subset of URI do share a common syntax for representing
hierarchical relationships within the namespace. This "generic URI"
syntax consists of a sequence of four main components:
<scheme>://<authority><path>?<query>
来源：
争议
这个答案是正确的，但是有关final fields的部分是错误的 - 这与回答无关 - Boris Treukhov
@BorisTreukhov - 请向我们详细说明您所说的“有关final fields的部分是不正确的”是什么意思 - 问题 - 如何获得uri以构造可以解析的方式（uri如何解析？请参见答案）。
package android.net;
/**
* Immutable URI reference. A URI reference includes a URI and a fragment, the
* component of the URI following a '#'. Builds and parses URI references
* which conform to
* <a href="http://www.faqs.org/rfcs/rfc2396.html">RFC 2396</a>.
*
* <p>In the interest of performance, this class performs little to no
* validation. Behavior is undefined for invalid input. This class is very
* forgiving--in the face of invalid input, it will return garbage
* rather than throw an exception unless otherwise specified.
*/
public abstract class Uri implements Parcelable, Comparable<Uri> { ... }
Uri 而不是 URI。Uri 是 Android 特有的。 - Rajan PrasadUri.Builder代替字符串连接。 Uri imageUri = (new Uri.Builder())
.scheme(ContentResolver.SCHEME_ANDROID_RESOURCE)
.authority(resources.getResourcePackageName(resourceId))
.appendPath(resources.getResourceTypeName(resourceId))
.appendPath(resources.getResourceEntryName(resourceId))
.build()
这就是你真正需要的：
Uri imageUri = Uri.parse(ContentResolver.SCHEME_ANDROID_RESOURCE +
"://" + getResources().getResourcePackageName(R.drawable.ic_launcher)
+ '/' + getResources().getResourceTypeName(R.drawable.ic_launcher) + '/' + getResources().getResourceEntryName(R.drawable.ic_launcher) );
in most simple form...
Uri uri = Uri.parse("android.resource://" + getPackageName() + "/" + R.drawable.book);
InputStream iStream = getContentResolver().openInputStream(uri);
“book”是drawable文件夹中文件的名称。
Uri.parse()不应该抛出这个异常。当您解析一个Uri时，它只检查是否为空引用，而不是实际解析它。 - Michaelstream和toString()吗？ - cagcak