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【移動應用開發技術】還沒弄懂四大組件？帶你全面解析ContentProvider篇
喜歡的小伙伴歡迎關注，我會定期分享Android知識點及解析，還會不斷更新的BATJ面試專題，歡迎大家前來探討交流，如有好的文章也歡迎投稿。1.什么是ContentProviderContentProvider，是自身APP開放給第三方APP的，用于訪問自身數據庫數據的接口。第三方APP可以通過該接口，對指定的數據進行增刪改查。那么如何定義自身的ContentProvider接口呢？在回答問題之前，先來關注一下Uri。2.什么是Uri原因在于，uri是ContentProvider解析外部請求（或者說是，第三方訪問自身數據庫）的關鍵參數。Uri的字符串格式如下content://package/table/idcontent://package/table/id例如content://com.breakloop.sqlitehelperdemo/hero/1content://com.breakloop.sqlitehelperdemo/hero/1從上方Uri示例中，可以獲取到以下信息。第三方APP想要訪問com.breakloop.sqlitehelperdemo的數據庫。至于哪個，由contentProvider內部映射指定。訪問表hero。至于表名是不是真為hero，也由contentProvider說了算。訪問id為1的數據。至于是不是id代表的具體含義，解釋權也歸contentProvider。那么，第三方APP將Uri傳入后，ContentProvider如何將其map為具體的數據庫操作呢？這便有了UriMatcher工具類的引入。3.UriMatcher該工具類，可以將Uri映射為int類型的行為代碼。行為代碼，可以看做是ContentProvider自定義的枚舉類型。而不同的行為代碼，綁定不同的數據庫操作。我們先來看一下，Uri與行為代碼的映射關系
public
final
static
String
AUTHORITY="com.breakloop.contentproviderdemo1";
public
final
static
int
BY_NAME=1;
public
final
static
int
BY_AGE=2;
public
final
static
int
BY_SEX=3;
public
final
static
int
BY_NONE=0;
public
final
static
String
PATH_BY_NAME=DBConst.TABLE_PERSON+"/ByName/*";
public
final
static
String
PATH_BY_AGE=DBConst.TABLE_PERSON+"/ByAge/#";
public
final
static
String
PATH_BY_SEX=DBConst.TABLE_PERSON+"/BySex/*";
}static
{
matcher=new
UriMatcher(UriMatcher.NO_MATCH);
matcher.addURI(MatcherConst.AUTHORITY,MatcherConst.PATH_BY_NAME,MatcherConst.BY_NAME);
matcher.addURI(MatcherConst.AUTHORITY,MatcherConst.PATH_BY_AGE,MatcherConst.BY_AGE);
matcher.addURI(MatcherConst.AUTHORITY,MatcherConst.PATH_BY_SEX,MatcherConst.BY_SEX);
matcher.addURI(MatcherConst.AUTHORITY,DBConst.TABLE_PERSON,MatcherConst.BY_NONE);
}在上面的示例中，UriMatch綁定了四個Uri，并將各個Uri映射為四個行為代碼。其中，用到了轉義符。#代表任意數字，*代表任意字母。那么如何將行為代碼映射為具體的數據庫操作呢？，換句話說，在哪兒使用UriMatcher呢？當然是ContentProvider中！！！在ContentProvider中的增刪改查方法中，完成操作映射。我們來看一下，ContentProvider的創建。4.ContentProvider的創建先用AndroidStudio創建一個ContentProvider.創建過程中，需要提供AUTHORITY,ContentProvider生成后，AndroidStudio將自動幫助ContentProvider在Manifest中進行注冊。接下來，我們看看ContentProvider的結構。5.ContentProvider的結構import
android.content.ContentProvider;import
android.content.ContentValues;import
android.content.UriMatcher;import
android.database.Cursor;import
.Uri;public
class
MyContentProvider
extends
ContentProvider
{
public
MyContentProvider()
{
}
@Override
public
int
delete(Uri
uri,
String
selection,
String[]
selectionArgs)
{
//
Implement
this
to
handle
requests
to
delete
one
or
more
rows.
throw
new
UnsupportedOperationException("Not
yet
implemented");
}
@Override
public
String
getType(Uri
uri)
{
//
TODO:
Implement
this
to
handle
requests
for
the
MIME
type
of
the
data
//
at
the
given
URI.
throw
new
UnsupportedOperationException("Not
yet
implemented");
}
@Override
public
Uri
insert(Uri
uri,
ContentValues
values)
{
//
TODO:
Implement
this
to
handle
requests
to
insert
a
new
row.
throw
new
UnsupportedOperationException("Not
yet
implemented");
}
@Override
public
boolean
onCreate()
{
//
TODO:
Implement
this
to
initialize
your
content
provider
on
startup.
return
false;
}
@Override
public
Cursor
query(Uri
uri,
String[]
projection,
String
selection,
String[]
selectionArgs,
String
sortOrder)
{
//
TODO:
Implement
this
to
handle
query
requests
from
clients.
throw
new
UnsupportedOperationException("Not
yet
implemented");
}
@Override
public
int
update(Uri
uri,
ContentValues
values,
String
selection,
String[]
selectionArgs)
{
//
TODO:
Implement
this
to
handle
requests
to
update
one
or
more
rows.
throw
new
UnsupportedOperationException("Not
yet
implemented");
}
}一共七個方法。包括一個構造方法，四個數據庫方法（增刪改查），一個初始化方法（onCreate）,還有一個getType。關于getType，我們之后解釋。關于構造方法，沒什么可解釋的。關于初始化方法，當返回true時，表明初始化成功，否則，失敗。由于我們要對數據庫進行操作，因此，需要獲取sqlite數據庫對象。public
boolean
onCreate()
{
helper=new
mySqliteHelper(getContext(),DBConst.DB_NAME,null,1);
return
true;
}關于數據庫方法，我們看到傳參中存在Uri，因此，這里需要用到UirMatcher了。我們將剛才的UriMatcher代碼段，加入MyContentProvider.這樣，我們就可以在各個數據庫方法中，解析Uri了。同時，由于sqlite數據庫對象的存在，進而可以對數據庫進行相應操作。6.行為代碼Mapping數據庫操作我們先看一下最簡單的插入操作。
public
Uri
insert(Uri
uri,
ContentValues
values)
{
Uri
returnUri=null;
SQLiteDatabase
db=helper.getWritableDatabase();
switch
(matcher.match(uri)){
case
MatcherConst.BY_NONE:
long
recordID=db.insert(DBConst.TABLE_PERSON,null,values);
returnUri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/"+recordID);
break;
default:
break;
}
return
returnUri;
}再來看一下稍微復雜的查詢。
public
Cursor
query(Uri
uri,
String[]
projection,
String
selection,
String[]
selectionArgs,
String
sortOrder)
{
Cursor
cursor=null;
SQLiteDatabase
db=helper.getReadableDatabase();
switch
(matcher.match(uri)){
case
MatcherConst.BY_NONE:
cursor=db.query(DBConst.TABLE_PERSON,projection,selection,selectionArgs,null,null,sortOrder);
break;
case
MatcherConst.BY_AGE:
cursor=db.query(DBConst.TABLE_PERSON,projection,DBConst.COLUMN_AGE+"=?",new
String[]{uri.getPathSegments().get(2)},null,null,sortOrder);
break;
case
MatcherConst.BY_SEX:
cursor=db.query(DBConst.TABLE_PERSON,projection,DBConst.COLUMN_SEX+"=?",new
String[]{uri.getPathSegments().get(2)},null,null,sortOrder);
break;
case
MatcherConst.BY_NAME:
cursor=db.query(DBConst.TABLE_PERSON,projection,DBConst.COLUMN_NAME+"=?",new
String[]{uri.getPathSegments().get(2)},null,null,sortOrder);
break;
default:
break;
}
return
cursor;
}這里需要注意的是，如何取Uri中的傳入數據。使用的獲取方法是uri.getPathSegments().get(index)。該方法獲取的是AUTHORITY后面的String部分。然后，以”/”為分隔符，生成String[]。接著是更新操作。
@Override
public
int
update(Uri
uri,
ContentValues
values,
String
selection,
String[]
selectionArgs)
{
int
recordID=0;
SQLiteDatabase
db=helper.getWritableDatabase();
switch
(matcher.match(uri)){
case
MatcherConst.BY_NONE:
recordID=db.update(DBConst.TABLE_PERSON,values,null,null);
break;
case
MatcherConst.BY_AGE:
recordID=db.update(DBConst.TABLE_PERSON,values,DBConst.COLUMN_AGE+"=?",new
String[]{uri.getPathSegments().get(2)});
break;
case
MatcherConst.BY_SEX:
recordID=db.update(DBConst.TABLE_PERSON,values,DBConst.COLUMN_SEX+"=?",new
String[]{uri.getPathSegments().get(2)});
break;
case
MatcherConst.BY_NAME:
recordID=db.update(DBConst.TABLE_PERSON,values,DBConst.COLUMN_NAME+"=?",new
String[]{uri.getPathSegments().get(2)});
break;
default:
break;
}
return
recordID;
}還有刪除。
public
int
delete(Uri
uri,
String
selection,
String[]
selectionArgs)
{
int
recordID=0;
SQLiteDatabase
db=helper.getWritableDatabase();
switch
(matcher.match(uri)){
case
MatcherConst.BY_NONE:
recordID=db.delete(DBConst.TABLE_PERSON,null,null);
break;
case
MatcherConst.BY_AGE:
recordID=db.delete(DBConst.TABLE_PERSON,DBConst.COLUMN_AGE+"=?",new
String[]{uri.getPathSegments().get(2)});
break;
case
MatcherConst.BY_SEX:
recordID=db.delete(DBConst.TABLE_PERSON,DBConst.COLUMN_SEX+"=?",new
String[]{uri.getPathSegments().get(2)});
break;
case
MatcherConst.BY_NAME:
recordID=db.delete(DBConst.TABLE_PERSON,DBConst.COLUMN_NAME+"=?",new
String[]{uri.getPathSegments().get(2)});
break;
default:
break;
}
return
recordID;
}那么，第三方如何調用ContentProvider呢？7.ContentProvider的使用這里，我們新建一個工程contentproviderdemo2，在必要的位置使用方法publicContentResolvergetContentResolver()publicContentResolvergetContentResolver()獲取ContentProvider實例，之后便可傳入Uri，調用數據庫相關方法了。例如，我們插入四條記錄。
Uri
returnUri=null;
ContentResolver
resolver=getContentResolver();
Uri
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
ContentValues
values=new
ContentValues();
values.put(DBConst.COLUMN_NAME,"A");
values.put(DBConst.COLUMN_AGE,10);
values.put(DBConst.COLUMN_SEX,"Male");
returnUri=resolver.insert(uri,values);
if(returnUri!=null)
Log.i(TAG,
"return
Uri
=
"+returnUri.toString());
values.put(DBConst.COLUMN_NAME,"B");
values.put(DBConst.COLUMN_AGE,11);
values.put(DBConst.COLUMN_SEX,"Male");
returnUri=resolver.insert(uri,values);
if(returnUri!=null)
Log.i(TAG,
"return
Uri
=
"+returnUri.toString());
values.put(DBConst.COLUMN_NAME,"C");
values.put(DBConst.COLUMN_AGE,12);
values.put(DBConst.COLUMN_SEX,"Female");
returnUri=resolver.insert(uri,values);
if(returnUri!=null)
Log.i(TAG,
"return
Uri
=
"+returnUri.toString());
values.put(DBConst.COLUMN_NAME,"D");
values.put(DBConst.COLUMN_AGE,13);
values.put(DBConst.COLUMN_SEX,"Female");
returnUri=resolver.insert(uri,values);
if(returnUri!=null)
Log.i(TAG,
"return
Uri
=
"+returnUri.toString());我們看一下輸出結果。I/com.breakloop.contentproviderdemo2.MainActivity:
return
Uri
=
content://com.breakloop.contentproviderdemo1/PERSON/1I/com.breakloop.contentproviderdemo2.MainActivity:
return
Uri
=
content://com.breakloop.contentproviderdemo1/PERSON/2I/com.breakloop.contentproviderdemo2.MainActivity:
return
Uri
=
content://com.breakloop.contentproviderdemo1/PERSON/3I/com.breakloop.contentproviderdemo2.MainActivity:
return
Uri
=
content://com.breakloop.contentproviderdemo1/PERSON/4既然，寫入成功，那我們查詢一下。
public
void
selectRecord(){
Uri
uri;
String
name="A";
int
age=11;
String
sex="Male";
Log.i(TAG,
"Select
by
Name");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByName/"+name);
selectRecord(uri);
Log.i(TAG,
"Select
by
Age");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByAge/"+age);
selectRecord(uri);
Log.i(TAG,
"Select
by
Sex");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/BySex/"+sex);
selectRecord(uri);
Log.i(TAG,
"Select
All");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
selectRecord(uri);
}
private
void
selectRecord(Uri
uri){
Cursor
cursor;
cursor=resolver.query(uri,new
String[]{DBConst.COLUMN_AGE,
DBConst.COLUMN_NAME,
DBConst.COLUMN_SEX},null,null,null);
if(cursor!=null){
while(cursor.moveToNext()){
Log.i(TAG,
"name
=
"+cursor.getString(1)+
"
age
=
"+cursor.getInt(0)
+"
"+cursor.getString(2));
}
}
}輸出結果如下I/com.breakloop.contentproviderdemo2.MainActivity:
Select
by
Name
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
A
age
=
10
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
Select
by
Age
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
B
age
=
11
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
Select
by
Sex
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
A
age
=
10
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
B
age
=
11
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
Select
All
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
A
age
=
10
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
B
age
=
11
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
C
age
=
12
Female
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
D
age
=
13
Female我們再來更新一下。
public
void
updateRecord(){
Uri
uri;
String
name="A";
int
age=11;
String
sex="Female";
ContentValues
values=new
ContentValues();
Log.i(TAG,
"Update
by
Name");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByName/"+name);
values.put(DBConst.COLUMN_NAME,name+name);
update(uri,values);
Log.i(TAG,
"Update
by
Age");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByAge/"+age);
values.clear();
values.put(DBConst.COLUMN_AGE,14);
update(uri,values);
Log.i(TAG,
"Update
by
Sex");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/BySex/"+sex);
values.clear();
values.put(DBConst.COLUMN_AGE,15);
update(uri,values);
Log.i(TAG,
"Update
All");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
values.put(DBConst.COLUMN_SEX,"Male");
update(uri,values);
Log.i(TAG,
"Select
All");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
selectRecord(uri);
}
private
void
update(Uri
uri,ContentValues
values){
int
count;
count=resolver.update(uri,values,null,null);
Log.i(TAG,
"update
"+count+"
record");
}結果如下I/com.breakloop.contentproviderdemo2.MainActivity:
Update
by
Name
I/com.breakloop.contentproviderdemo2.MainActivity:
update
1
record
I/com.breakloop.contentproviderdemo2.MainActivity:
Update
by
Age
I/com.breakloop.contentproviderdemo2.MainActivity:
update
1
record
I/com.breakloop.contentproviderdemo2.MainActivity:
Update
by
Sex
I/com.breakloop.contentproviderdemo2.MainActivity:
update
2
record
I/com.breakloop.contentproviderdemo2.MainActivity:
Update
All
I/com.breakloop.contentproviderdemo2.MainActivity:
update
4
record
I/com.breakloop.contentproviderdemo2.MainActivity:
Select
All
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
AA
age
=
15
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
B
age
=
15
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
C
age
=
15
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
D
age
=
15
Male都不要了，刪除！（這里是對更新前的數據庫進行的操作）
public
void
deleteRecord(){
Uri
uri;
String
name="A";
int
age=11;
String
sex="Female";
Log.i(TAG,
"Delete
by
Name");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByName/"+name);
delete(uri);
Log.i(TAG,
"Select
All");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
selectRecord(uri);
Log.i(TAG,
"Delete
by
Age");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/ByAge/"+age);
delete(uri);
Log.i(TAG,
"Select
All");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
selectRecord(uri);
Log.i(TAG,
"Delete
by
Sex");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON+"/BySex/"+sex);
delete(uri);
Log.i(TAG,
"Select
All");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
selectRecord(uri);
Log.i(TAG,
"Delete
All");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
delete(uri);
Log.i(TAG,
"Select
All");
uri=Uri.parse("content://"+MatcherConst.AUTHORITY+"/"+DBConst.TABLE_PERSON);
selectRecord(uri);
}
private
void
delete(Uri
uri){
int
count;
count=resolver.delete(uri,null,null);
Log.i(TAG,
"delete
"+count+"
record");
}結果如下I/com.breakloop.contentproviderdemo2.MainActivity:
delete
1
record
I/com.breakloop.contentproviderdemo2.MainActivity:
Select
All
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
B
age
=
11
Male
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
C
age
=
12
Female
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
D
age
=
13
Female
I/com.breakloop.contentproviderdemo2.MainActivity:
Delete
by
Age
I/com.breakloop.contentproviderdemo2.MainActivity:
delete
1
record
I/com.breakloop.contentproviderdemo2.MainActivity:
Select
All
I/com.breakloop.contentproviderdemo2.MainActivity:
name
=
C
age
=
12
Female
I/com.breakloop.contentproviderdemo2.
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