为什么80%的码农都做不了架构师？>>> 
Android应用开发之（通过ClipboardManager, ClipData进行复制粘贴）
Android Developer:
在开发一些系统应用的时候，我们会用到Android的剪贴板功能，比如将文本文件、或者其他格式的内容复制到剪贴板或者从剪贴板获取数据等操作。Android平台中每个常规的应用运行在自己的进程空间中，相对于Win32而言Android上之间的进程间传递主要有IPC、剪切板。当然今天我们说下最简单的ClipboardManager。使用剪切板可以直接实现数据的传输。整个实现比较简单，注意剪切板中的类型判断。
使用起来很简单，系统给我们提供了很方便的接口，如下文本信息复制如下所示：
//获取剪贴板管理服务 ClipboardManager cm =(ClipboardManager) context.getSystemService(Context.CLIPBOARD_SERVICE); //将文本数据复制到剪贴板 cm.setText(message); //读取剪贴板数据 cm.getText();public void setClipboard(String text) { ClipboardManager clipboard = (ClipboardManager)getSystemService(Context.CLIPBOARD_SERVICE); clipboard.setText(text); } public String getClipboard() { ClipboardManager clipboard = (ClipboardManager)getSystemService(Context.CLIPBOARD_SERVICE); return clipboard.getText().toString(); }ClipData代表剪贴板中剪切数据。它有一个或多个Item实例，每个可容纳一个或多个数据项。 ClipData包含ClipDescription，用来描述剪贴内容的重要元数据。尤其是getDescription（）.getMimeType（INT）必须返回正确的MIME类型。为了正确的设置剪贴内容的MIME类型，建议使用newPlainText（CharSequence，CharSequence的），newUri（ContentResolver，CharSequence中，URI），newIntent（CharSequence, Intent）构造ClipData。每个Item的实例可以是三大数据类型之一：text，intent，URI。详情请参阅ClipData.Item
粘贴数据
为了获取剪贴板中的数据，应用程序必须正确解析数据；如果CipData.Item包含的信息为文本或者Intent类型，有一点需要说明：文本只能解析为文本，intent通常用来当中快捷方式或者其他的动作类型；如果你只是想获取文本内容，你可以通过Item.coerceToText（）方法强制获取，这样就不需要考虑MIME类型，应为所有的item都会被强制转换为文本。
复杂的数据类型通常用URL来完成粘贴。允许接受者以URI方式从ContentProvider的获取数据。剪贴时需要填写正确的MIME类型; 如：newUri（ContentResolver，CharSequence，URI）这样才能被正确的处理。
下面是NotePad应用粘贴的例子。当从剪贴板中接受数据时，如果剪贴板中包含已有note的URI引用时，根据URI复制其结构到新的Note中，否则通过根据获取的文本内容作为新的笔记内容：
/** * A helper method that replaces the note's data with the contents of the clipboard. */ private final void performPaste() { // Gets a handle to the Clipboard Manager ClipboardManager clipboard = (ClipboardManager) getSystemService(Context.CLIPBOARD_SERVICE); // Gets a content resolver instance ContentResolver cr = getContentResolver(); // Gets the clipboard data from the clipboard ClipData clip = clipboard.getPrimaryClip(); if (clip != null) { String text=null; String title=null; // Gets the first item from the clipboard data ClipData.Item item = clip.getItemAt(0); // Tries to get the item's contents as a URI pointing to a note Uri uri = item.getUri(); // Tests to see that the item actually is an URI, and that the URI // is a content URI pointing to a provider whose MIME type is the same // as the MIME type supported by the Note pad provider. if (uri != null && NotePad.Notes.CONTENT_ITEM_TYPE.equals(cr.getType(uri))) { // The clipboard holds a reference to data with a note MIME type. This copies it. Cursor orig = cr.query( uri, // URI for the content provider PROJECTION, // Get the columns referred to in the projection null, // No selection variables null, // No selection variables, so no criteria are needed null // Use the default sort order ); // If the Cursor is not null, and it contains at least one record // (moveToFirst() returns true), then this gets the note data from it. if (orig != null) { if (orig.moveToFirst()) { int colNoteIndex = mCursor.getColumnIndex(NotePad.Notes.COLUMN_NAME_NOTE); int colTitleIndex = mCursor.getColumnIndex(NotePad.Notes.COLUMN_NAME_TITLE); text = orig.getString(colNoteIndex); title = orig.getString(colTitleIndex); } // Closes the cursor. orig.close(); } } // If the contents of the clipboard wasn't a reference to a note, then // this converts whatever it is to text. if (text == null) { text = item.coerceToText(this).toString(); } // Updates the current note with the retrieved title and text. updateNote(text, title); } }很多应用可以处理多种类型的数据，例如：E_mail应用希望用户粘贴图片或者其他二进制文件作为附件。这就需要通过ContentResolver的getStreamTypes(Uri, String)和openTypedAssetFileDescriptor(Uri,String,android.os.Bundle)方法处理。这需要客户端检测一个特定的内容URI以流的方式处理数据。
如下面是Item.coerceToText的实现：
public CharSequence coerceToText(Context context) { // If this Item has an explicit textual value, simply return that. if (mText != null) { return mText; } // If this Item has a URI value, try using that. if (mUri != null) { // First see if the URI can be opened as a plain text stream // (of any sub-type). If so, this is the best textual // representation for it. FileInputStream stream = null; try { // Ask for a stream of the desired type. AssetFileDescriptor descr = context.getContentResolver() .openTypedAssetFileDescriptor(mUri, "text/*", null); stream = descr.createInputStream(); InputStreamReader reader = new InputStreamReader(stream, "UTF-8"); // Got it... copy the stream into a local string and return it. StringBuilder builder = new StringBuilder(128); char[] buffer = new char[8192]; int len; while ((len=reader.read(buffer)) > 0) { builder.append(buffer, 0, len); } return builder.toString(); } catch (FileNotFoundException e) { // Unable to open content URI as text... not really an // error, just something to ignore. } catch (IOException e) { // Something bad has happened. Log.w("ClippedData", "Failure loading text", e); return e.toString(); } finally { if (stream != null) { try { stream.close(); } catch (IOException e) { } } } // If we couldn't open the URI as a stream, then the URI itself // probably serves fairly well as a textual representation. return mUri.toString(); } // Finally, if all we have is an Intent, then we can just turn that // into text. Not the most user-friendly thing, but it's something. if (mIntent != null) { return mIntent.toUri(Intent.URI_INTENT_SCHEME); } // Shouldn't get here, but just in case... return ""; }复制数据
做为复制的源数据，应用要构造容易被接受解析的剪贴数据。如果要复制包含文本，Intent，或者URI，简单的方式是使用ClipData.Item包含相应的类型数据；
复杂的数据类型要求支持以ContentProvide方式描述和生成被接受的数据，常用的解决方案是以URI的方式复制数据，URI有复杂结构的数据组成，只有理解这种结果的应用才能接受处理这样的数据；
对于不具有内在的数据结构知识的应用，可使用任意可接受的数据流类型。这是通过实现ContentProvider的getStreamTypes（URI，String）和openTypedAssetFile（URI字符串，android.os.Bundle）方法进行获取。
回到记事本应用程序的例子，它是将要复制的内容以URI的传递的
/** * This describes the MIME types that are supported for opening a note * URI as a stream. */ static ClipDescription NOTE_STREAM_TYPES = new ClipDescription(null, new String[] { ClipDescription.MIMETYPE_TEXT_PLAIN }); /** * Returns the types of available data streams. URIs to specific notes are supported. * The application can convert such a note to a plain text stream. * * @param uri the URI to analyze * @param mimeTypeFilter The MIME type to check for. This method only returns a data stream * type for MIME types that match the filter. Currently, only text/plain MIME types match. * @return a data stream MIME type. Currently, only text/plan is returned. * @throws IllegalArgumentException if the URI pattern doesn't match any supported patterns. */ @Override public String[] getStreamTypes(Uri uri, String mimeTypeFilter) { /** * Chooses the data stream type based on the incoming URI pattern. */ switch (sUriMatcher.match(uri)) { // If the pattern is for notes or live folders, return null. Data streams are not // supported for this type of URI. case NOTES: case LIVE_FOLDER_NOTES: return null; // If the pattern is for note IDs and the MIME filter is text/plain, then return // text/plain case NOTE_ID: return NOTE_STREAM_TYPES.filterMimeTypes(mimeTypeFilter); // If the URI pattern doesn't match any permitted patterns, throws an exception. default: throw new IllegalArgumentException("Unknown URI " + uri); } } /** * Returns a stream of data for each supported stream type. This method does a query on the * incoming URI, then uses * {@link android.content.ContentProvider#openPipeHelper(Uri, String, Bundle, Object, * PipeDataWriter)} to start another thread in which to convert the data into a stream. * * @param uri The URI pattern that points to the data stream * @param mimeTypeFilter A String containing a MIME type. This method tries to get a stream of * data with this MIME type. * @param opts Additional options supplied by the caller. Can be interpreted as * desired by the content provider. * @return AssetFileDescriptor A handle to the file. * @throws FileNotFoundException if there is no file associated with the incoming URI. */ @Override public AssetFileDescriptor openTypedAssetFile(Uri uri, String mimeTypeFilter, Bundle opts) throws FileNotFoundException { // Checks to see if the MIME type filter matches a supported MIME type. String[] mimeTypes = getStreamTypes(uri, mimeTypeFilter); // If the MIME type is supported if (mimeTypes != null) { // Retrieves the note for this URI. Uses the query method defined for this provider, // rather than using the database query method. Cursor c = query( uri, // The URI of a note READ_NOTE_PROJECTION, // Gets a projection containing the note's ID, title, // and contents null, // No WHERE clause, get all matching records null, // Since there is no WHERE clause, no selection criteria null // Use the default sort order (modification date, // descending ); // If the query fails or the cursor is empty, stop if (c == null || !c.moveToFirst()) { // If the cursor is empty, simply close the cursor and return if (c != null) { c.close(); } // If the cursor is null, throw an exception throw new FileNotFoundException("Unable to query " + uri); } // Start a new thread that pipes the stream data back to the caller. return new AssetFileDescriptor( openPipeHelper(uri, mimeTypes[0], opts, c, this), 0, AssetFileDescriptor.UNKNOWN_LENGTH); } // If the MIME type is not supported, return a read-only handle to the file. return super.openTypedAssetFile(uri, mimeTypeFilter, opts); } /** * Implementation of {@link android.content.ContentProvider.PipeDataWriter} * to perform the actual work of converting the data in one of cursors to a * stream of data for the client to read. */ @Override public void writeDataToPipe(ParcelFileDescriptor output, Uri uri, String mimeType, Bundle opts, Cursor c) { // We currently only support conversion-to-text from a single note entry, // so no need for cursor data type checking here. FileOutputStream fout = new FileOutputStream(output.getFileDescriptor()); PrintWriter pw = null; try { pw = new PrintWriter(new OutputStreamWriter(fout, "UTF-8")); pw.println(c.getString(READ_NOTE_TITLE_INDEX)); pw.println(""); pw.println(c.getString(READ_NOTE_NOTE_INDEX)); } catch (UnsupportedEncodingException e) { Log.w(TAG, "Ooops", e); } finally { c.close(); if (pw != null) { pw.flush(); } try { fout.close(); } catch (IOException e) { } } }not复制操作现在只是简单的构造UPI：
case R.id.context_copy: // Gets a handle to the clipboard service. ClipboardManager clipboard = (ClipboardManager) getSystemService(Context.CLIPBOARD_SERVICE); // Copies the notes URI to the clipboard. In effect, this copies the note itself clipboard.setPrimaryClip(ClipData.newUri( // new clipboard item holding a URI getContentResolver(), // resolver to retrieve URI info "Note", // label for the clip noteUri) // the URI ); // Returns to the caller and skips further processing. return true;注 如果粘贴操作需要文本（例如粘贴到编程器中）coerceToText(Context)方式会通知内容提供者将URI转换为URL；
转 ：http://wenzhutech.diandian.com/post/2012-06-07/40028957456