36.Android 自定义ContentProviderContentProvider 介绍
有一种情景：假如A应用存储的数据，B也用到。那么，要怎么共享数据呢？
其实有很多种解决办法，比如存在SD卡上、网络等等。
其实Android上的相册、联系人也都是Google给Android系统写的App。也提供了对应的一套API给我们调用到其相应的数据，这就是ContentProvider。
ContentProvider是获取数据和存储都用的是统一的封装接口，涉及到Uri的概念。
当然了，如果用到Uri了，我们可以使用Google提供的工具类 UriMatcher 和 ContentUris ，以下会讲到这些。
ContentProvider 优点
可以获取系统原生一些App的数据。
不同App之间可以共享数据。
对数据进行封装，存储和获取提供统一的API。
Android 自带的ContentProvider
如果想获取一些系统自带App的数据，可以参考： android.provider 包下的ContentProvider。
ContentProvider Uri 结构
content://com.camnter.content.provider/message/6
content:// ：Scheme
com.camnter.content.provider ：Authority（主机名），这个ContentProvider的唯一标识。
message ：Table（表名）
6 ：Id
几个例子： content://com.camnter.content.provider/message：表示操作message表的所有记录。
content://com.camnter.content.provider/message/6：表示操作message表的Id = 6的记录。
content://com.camnter.content.provider/message/6/content：表示操作message表的Id = 6的记录的content字段。
Google Uri 工具类
UriMatcher ：
public void addURI(String authority, String path, int code)：添加Uri，Uri会被添加到一个ArrayList里，提供match(Uri uri)去匹配。
public int match(Uri uri)：根据Uri匹配改Uri是否被添加。
ContentUris：
public static long parseId(Uri contentUri)：解析Uri取得Id。
public static Uri.Builder appendId(Uri.Builder builder, long id)：添加Id。
public static Uri withAppendedId(Uri contentUri, long id)：添加Id。
UriMatcher 解析
ContentUris的源码特别简单，整个类就调用了Uri类的两个方法 T T# 。
所以就看看UriMatcher源码吧。
由于对其他类的依赖不多，我就自定义了一份UriMatcher。
import android.net.Uri;import java.util.ArrayList;import java.util.List;/**Utility class to aid in matching URIs in content providers.<p>To use this class, build up a tree of <code>UriMatcher</code> objects.For example:<pre>private static final int PEOPLE = 1;private static final int PEOPLE_ID = 2;private static final int PEOPLE_PHONES = 3;private static final int PEOPLE_PHONES_ID = 4;private static final int PEOPLE_CONTACTMETHODS = 7;private static final int PEOPLE_CONTACTMETHODS_ID = 8;private static final int DELETED_PEOPLE = 20;private static final int PHONES = 9;private static final int PHONES_ID = 10;private static final int PHONES_FILTER = 14;private static final int CONTACTMETHODS = 18;private static final int CONTACTMETHODS_ID = 19;private static final int CALLS = 11;private static final int CALLS_ID = 12;private static final int CALLS_FILTER = 15;private static final UriMatcher sURIMatcher = new UriMatcher(UriMatcher.NO_MATCH);static{sURIMatcher.addURI(“contacts”, “people”, PEOPLE);sURIMatcher.addURI(“contacts”, “people/#”, PEOPLE_ID);sURIMatcher.addURI(“contacts”, “people/#/phones”, PEOPLE_PHONES);sURIMatcher.addURI(“contacts”, “people/#/phones/#”, PEOPLE_PHONES_ID);sURIMatcher.addURI(“contacts”, “people/#/contact_methods”, PEOPLE_CONTACTMETHODS);sURIMatcher.addURI(“contacts”, “people/#/contact_methods/#”, PEOPLE_CONTACTMETHODS_ID);sURIMatcher.addURI(“contacts”, “deleted_people”, DELETED_PEOPLE);sURIMatcher.addURI(“contacts”, “phones”, PHONES);sURIMatcher.addURI(“contacts”, “phones/filter/*”, PHONES_FILTER);sURIMatcher.addURI(“contacts”, “phones/#”, PHONES_ID);sURIMatcher.addURI(“contacts”, “contact_methods”, CONTACTMETHODS);sURIMatcher.addURI(“contacts”, “contact_methods/#”, CONTACTMETHODS_ID);sURIMatcher.addURI(“call_log”, “calls”, CALLS);sURIMatcher.addURI(“call_log”, “calls/filter/*”, CALLS_FILTER);sURIMatcher.addURI(“call_log”, “calls/#”, CALLS_ID);}</pre><p>Starting from API level {@link android.os.Build.VERSION_CODES#JELLY_BEAN_MR2}, paths can start with a leading slash. For example:<pre>sURIMatcher.addURI(“contacts”, “/people”, PEOPLE);</pre><p>Then when you need to match against a URI, call {@link #match}, providingthe URL that you have been given. You can use the result to build a query,return a type, insert or delete a row, or whatever you need, without duplicatingall of the if-else logic that you would otherwise need. For example:<pre>public String getType(Uri url){int match = sURIMatcher.match(url);switch (match){case PEOPLE:return “vnd.android.cursor.dir/person”;case PEOPLE_ID:return “vnd.android.cursor.item/person”;… snip …return “vnd.android.cursor.dir/snail-mail”;case PEOPLE_ADDRESS_ID:return “vnd.android.cursor.item/snail-mail”;default:return null;}}</pre>instead of:<pre>public String getType(Uri url){List<String> pathSegments = url.getPathSegments();if (pathSegments.size() >= 2) {if (“people”.equals(pathSegments.get(1))) {if (pathSegments.size() == 2) {return “vnd.android.cursor.dir/person”;} else if (pathSegments.size() == 3) {return “vnd.android.cursor.item/person”;… snip …return “vnd.android.cursor.dir/snail-mail”;} else if (pathSegments.size() == 3) {return “vnd.android.cursor.item/snail-mail”;}}}return null;}</pre>*/public class UriMatcher{public static final int NO_MATCH = -1;/*** Creates the root node of the URI tree.* 创建Uri树的根节点** @param code the code to match for the root URI*/public UriMatcher(int code){mCode = code;mWhich = -1;mChildren = new ArrayList<UriMatcher>();mText = null;}private UriMatcher(){mCode = NO_MATCH;mWhich = -1;mChildren = new ArrayList<UriMatcher>();mText = null;}/*** Add a URI to match, and the code to return when this URI is* matched. URI nodes may be exact match string, the token “*”* that matches any text, or the token “#” that matches only* numbers.* 添加一个URI匹配，并且这里添加code值会在这个URI匹配成功的时候返回。URI节点可能精确匹配字符串，* token为“*”的时候会匹配为text，token为“#”的时候只会匹配为数字* <p>* Starting from API level {@link android.os.Build.VERSION_CODES#JELLY_BEAN_MR2},* this method will accept a leading slash in the path.** @param authority the authority to match*ContentProvider的authority** @param path the path to match. * may be used as a wild card for* any text, and # may be used as a wild card for numbers.*匹配路径，*可能是作为一个通配符用于任何文本,和#可能用作通配符数字。** @param code the code that is returned when a URI is matched* against the given components. Must be positive.*该URI匹配成功时返回的code*/public void addURI(String authority, String path, int code){if (code < 0) {throw new IllegalArgumentException(“code ” + code + ” is invalid: it must be positive”);}String[] tokens = null;if (path != null) {String newPath = path;// Strip leading slash if present.if (path.length() > 0 && path.charAt(0) == ‘/’) {newPath = path.substring(1);}tokens = newPath.split(“/”);}int numTokens = tokens != null ? tokens.length : 0;UriMatcher node = this;for (int i = -1; i < numTokens; i++) {String token = i < 0 ? authority : tokens[i];ArrayList<UriMatcher> children = node.mChildren;int numChildren = children.size();UriMatcher child;int j;for (j = 0; j < numChildren; j++) {child = children.get(j);if (token.equals(child.mText)) {node = child;break;}}if (j == numChildren) {// Child not found, create itchild = new UriMatcher();if (token.equals(“#”)) {child.mWhich = NUMBER;} else if (token.equals(“*”)) {child.mWhich = TEXT;} else {child.mWhich = EXACT;}child.mText = token;node.mChildren.add(child);node = child;}}node.mCode = code;}/*** Try to match against the path in a url.* 尝试匹配一个url的路径。** @param uriThe url whose path we will match against.*将匹配的url路径。** @return The code for the matched node (added using addURI),* or -1 if there is no matched node.*匹配节点设置的code（在使用addURI时，给对应URI设置code），*或者没有匹配节点，则反悔-1。*/public int match(Uri uri){final List<String> pathSegments = uri.getPathSegments();final int li = pathSegments.size();UriMatcher node = this;if (li == 0 && uri.getAuthority() == null) {return this.mCode;}for (int i=-1; i<li; i++) {String u = i < 0 ? uri.getAuthority() : pathSegments.get(i);ArrayList<UriMatcher> list = node.mChildren;if (list == null) {break;}node = null;int lj = list.size();for (int j=0; j<lj; j++) {UriMatcher n = list.get(j);which_switch:switch (n.mWhich) {case EXACT:if (n.mText.equals(u)) {node = n;}break;case NUMBER:int lk = u.length();for (int k=0; k<lk; k++) {char c = u.charAt(k);if (c < ‘0’ || c > ‘9’) {break which_switch;}}node = n;break;case TEXT:node = n;break;}if (node != null) {break;}}if (node == null) {return NO_MATCH;}}return node.mCode;}private static final int EXACT = 0;private static final int NUMBER = 1;private static final int TEXT = 2;private int mCode;private int mWhich;private String mText;private ArrayList<UriMatcher> mChildren;}
以上注释还有使用，Google告诉我们怎么使用UriMatcher的范例代码。
自定义 ContentProvider
代码都重复看过，都写上了注释。
没有了爱的语言，所有的文字都是乏味的
