IOS database persistence, ios Database

IOS database persistence, ios Database

Java code

1. -(Void) addObserver {
2. // Perform the operation when the program enters the background
3. UIApplication * app = [UIApplication sharedApplication];
4. [[Nsicationcenter center defacenter center] addObserver: self
5. Selector: @ selector (appwillresignActive) name: UIApplicationWillResignActiveNotification object: app];
6. }
7. -(Void) appwillresignActive {
8. NSLog (@ "listener test ");
9. }

-(Void) addObserver {

// Perform the operation when the program enters the background

UIApplication * app = [UIApplication sharedApplication];

[[Nsicationcenter center defacenter center] addObserver: self

Selector: @ selector (appwillresignActive) name: UIApplicationWillResignActiveNotification object: app];

}

-(Void) appwillresignActive {

NSLog (@ "listener test ");

}

Header Introduction

Java code

1. # Import "sqlite3.h"

# Import "sqlite3.h"

 

Java code

1. -(Void) makeDBinfo {
2. NSArray * documentsPaths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES );
4. NSString * databaseFilePath = [[documentsPaths objectAtIndex: 0] stringByAppendingPathComponent: @ "mydb"];
6. Char * errorMsg;
8. // Open or create a database
9. Sqlite3 * database;
11. If (sqlite3_open ([databaseFilePath UTF8String], & database )! = SQLITE_ OK ){
12. Sqlite3_close (database );
13. } Else {
14. NSLog (@ "open sqlite db OK .");
15. }
16. // Create a database table
18. Const char * createSql = "create table if not exists persons (id integer primary key autoincrement, name text )";
20. If (sqlite3_exec (database, createSql, NULL, NULL, & errorMsg) = SQLITE_ OK)
21. {
22. NSLog (@ "create table OK .");
23. } Else
24. {
25. // If errorMsg is used in multiple places, clear the string after each use, for example:
26. NSLog (@ "error: % s", errorMsg );
27. Sqlite3_free (errorMsg );
28. }
29. // Insert records into the table
30. Const char * insertSql = "insert into persons (name) values (\" James \")";
31. If (sqlite3_exec (database, insertSql, NULL, NULL, & errorMsg) = SQLITE_ OK)
32. {
33. NSLog (@ "insert OK .");
34. } Else
35. {
36. // If errorMsg is used in multiple places, clear the string after each use, for example:
37. NSLog (@ "error: % s", errorMsg );
38. Sqlite3_free (errorMsg );
39. }
41. // Statement is required for query of result sets:
42. Const char * selectSql = "select id, name from persons where name =? ";
43. Sqlite3_stmt * statement;
45. If (sqlite3_prepare_v2 (database, selectSql,-1, & statement, nil) = SQLITE_ OK ){
46. NSLog (@ "select OK .");
48. Sqlite3_bind_text (statement, 1, "Zhang San",-1, NULL );
51. While (sqlite3_step (statement) = SQLITE_ROW ){
52. Int _ id = sqlite3_column_int (statement, 0 );
53. NSString * name = [[NSString alloc] initWithCString :( char *) sqlite3_column_text (statement, 1) encoding: NSUTF8StringEncoding];
54. NSLog (@ "row> id % I, name % @", _ id, name );
55. }
57. Sqlite3_finalize (statement );
58. }
59. Sqlite3_close (database );
61. }

-(Void) makeDBinfo {

NSArray * documentsPaths = NSSearchPathForDirectoriesInDomains (NSDocumentDirectory, NSUserDomainMask, YES );

NSString * databaseFilePath = [[documentsPaths objectAtIndex: 0] stringByAppendingPathComponent: @ "mydb"];

Char * errorMsg;

// Open or create a database

Sqlite3 * database;

If (sqlite3_open ([databaseFilePath UTF8String], & database )! = SQLITE_ OK ){

Sqlite3_close (database );

} Else {

NSLog (@ "open sqlite db OK .");

}

// Create a database table

Const char * createSql = "create table if not exists persons (id integer primary key autoincrement, name text )";

If (sqlite3_exec (database, createSql, NULL, NULL, & errorMsg) = SQLITE_ OK)

{

NSLog (@ "create table OK .");

} Else

{

// If errorMsg is used in multiple places, clear the string after each use, for example:

NSLog (@ "error: % s", errorMsg );

Sqlite3_free (errorMsg );

}

// Insert records into the table

Const char * insertSql = "insert into persons (name) values (\" James \")";

If (sqlite3_exec (database, insertSql, NULL, NULL, & errorMsg) = SQLITE_ OK)

{

NSLog (@ "insert OK .");

} Else

{

// If errorMsg is used in multiple places, clear the string after each use, for example:

NSLog (@ "error: % s", errorMsg );

Sqlite3_free (errorMsg );

}

// Statement is required for query of result sets:

Const char * selectSql = "select id, name from persons where name =? ";

Sqlite3_stmt * statement;

If (sqlite3_prepare_v2 (database, selectSql,-1, & statement, nil) = SQLITE_ OK ){

NSLog (@ "select OK .");

Sqlite3_bind_text (statement, 1, "Zhang San",-1, NULL );

While (sqlite3_step (statement) = SQLITE_ROW ){

Int _ id = sqlite3_column_int (statement, 0 );

NSString * name = [[NSString alloc] initWithCString :( char *) sqlite3_column_text (statement, 1) encoding: NSUTF8StringEncoding];

NSLog (@ "row> id % I, name % @", _ id, name );

}

Sqlite3_finalize (statement );

}

Sqlite3_close (database );

 

}

 

Delete a table

 

Constchar * SQL _drop_table = "drop table if exists t ";

Constchar * SQL _create_table = "create table t (id int primary key, msg varchar (128 ))";

 

Sqlite3_exec (db, SQL _drop_table, 0, 0, & errmsg );

Sqlite3_exec (db, SQL _create_table, 0, 0, & errmsg );

 

Insert data

Sqlite3_exec (db, "insert into t (id, msg) values (1, 'ady liu')", NULL, NULL, & errmsg );

 

 

Pre-compile operation

Int I = 0;

Sqlite3_stmt * stmt;

Char ca [255];

 

// Prepare statement

Sqlite3_prepare_v2 (db, "insert into t (id, msg) values (?,?) ",-1, & stmt, 0 );

For (I = 10; I <20; I ++ ){

Sprintf (ca, "HELLO # % I", I );

Sqlite3_bind_int (stmt, 1, I );

Sqlite3_bind_text (stmt, 2, ca, strlen (ca), NULL );

Sqlite3_step (stmt );

Sqlite3_reset (stmt );

}

Sqlite3_finalize (stmt)

The pre-compilation operation is troublesome. The complete pre-compilation process is as follows:
Create a sqlite3_stmt object through sqlite3_prepare_v2 ()
Bind the pre-compiled field value through sqlite3_bind _ * ()
Use sqlite3_step () to execute an SQL statement
Use sqlite3_reset () to reset the pre-compiled statement. Repeat the operation twice.
Use sqlite3_finalize () to destroy resources

 

Pre-compiled SQL statements can contain the following forms:
?
? NNN
: VVV
@ VVV
$ VVV
NNN indicates a number, and VVV indicates a string.

 

If yes? Or? NNN, you can directly perform sqlite3_bind _ * (). If it is a string, you also need to obtain the corresponding index through sqlite3_bind_parameter_index () and then call sqlite3_bind. This is usually used to construct SQL statements with indefinite conditions (dynamic SQL statements ).

 

Query operations

Write

For more information about callback functions, see the preceding description. Declare a callback function.
Int print_record (void *, int, char **, char **);

Query code
// Select data
Ret = sqlite3_exec (db, "select * from t", print_record, NULL, & errmsg );
If (ret! = SQLITE_ OK ){
Fprintf (stderr, "query SQL error: % s \ n", errmsg );
}


Now we define the callback function, which is just a simple output field value.
Int print_record (void * params, int n_column, char ** column_value, char ** column_name ){
Int I;
For (I = 0; I <n_column; I ++ ){
Printf ("\ t % s", column_value [I]);
}
Printf ("\ n ");
Return 0;
}

 

Query operations without callback

Write

Define the variables used
Char ** dbresult; int j, nrow, ncolumn, index;
Query operations
// Select table
Ret = sqlite3_get_table (db, "select * from t", & dbresult, & nrow, & ncolumn, & errmsg );
If (ret = SQLITE_ OK ){
Printf ("query % I records. \ n", nrow );
Index = ncolumn;
For (I = 0; I <nrow; I ++ ){
Printf ("[% 2i]", I );
For (j = 0; j <ncolumn; j ++ ){
Printf ("% s", dbresult [index]);
Index ++;
}
Printf ("\ n ");
}
}
Sqlite3_free_table (dbresult );

Number of affected records

We can use the sqlite3_change (sqlite3 *) API to count the number of records affected by the last operation.
Ret = sqlite3_exec (db, "delete from t", NULL, NULL, & errmsg );

If (ret = SQLITE_ OK ){

Printf ("delete records: % I \ n", sqlite3_changes (db ));

}

 

Summary

 

Write

Here we have access to 13 SQLITE3 APIs:
Sqlite3_open ()
Sqlite3_exec ()
Sqlite3_close ()
Sqlite3_prepare_v2
Sqlite3_bind _*()
Sqlite3_bind_parameter_index ()
Sqlite3_step ()
Sqlite3_reset ()
Sqlite3_finalize ()
Sqlite3_get_table
Sqlite3_change ()
Sqlite3_free ()
Sqlite3_free_table ()
As of fact SQLITE3.7.14 () has provided a total of 204 API functions (http://www.sqlite.org/c3ref/funclist.html ).
However, there are about 6 streamlined API functions:
Sqlite3_open ()
Sqlite3_prepare ()
Sqlite3_step ()
Sqlite3_column ()
Sqlite3_finalize ()
Sqlite3_close ()
There are also 10 core APIs (four more on the basis of simplified APIs ):
Sqlite3_exec ()
Sqlite3_get_table ()
Sqlite3_reset ()
Sqlite3_bind ()
Therefore, it is easier to master.