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This article introduces you how to connect to the database in Android, the content is very detailed, interested friends can refer to, hope to be helpful to you.

Question: how to use Eclipse to develop android, how to connect to the database, mainly connect to the server on the company's website, and read data from the database there?

Android connects to the database

Android adopts relational database SQLite3, which is a lightweight embedded database supporting SQL. It has a wide range of embedded operations, and WM also uses SQLite3.

Nothing about excesses and principles will be mentioned in this article, but if you want to learn how to operate SQLite3 quickly, this is what you're looking for!

First of all, let's take a look at api, all the database-related interfaces and classes are under the .database and android.database.sqlite packages, although there are only two packages, but if your English is not good or too lazy, then you should be confused for a while, in fact, we really use few!

1. SQLiteOpenHelper (android.database.sqlite.SQLiteOpenHelper)

This is an abstract class, we all know about the abstract class, if you want to use it, you must inherit it!

There are few methods for this class, and there is a constructor

SQLiteOpenHelper (android.content.Context context, java.lang.String name,android.database.sqlite.SQLiteDatabase.CursorFactory factory, int version)

Parameters are not explained too much. Generally speaking, CursorFactory can send null directly.

Public void onCreate (SQLiteDatabase db)

This method is called when creating the database, so you should put the table creation operation into this method, and we will talk more about how to create the table later.

Public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion)

We can know from the method name that the method is updated. Yes, when the version changes, the system will call this method, so in this method, you should delete the existing table, and then manually call onCreate.

SQLiteDatabase getReadableDatabase ()

Readable SQLiteDatabase object

SQLiteDatabase getWritableDatabase ()

Get a writable SQLiteDatabase object

2. SQLiteDatabase (android.database.sqlite.SQLiteDatabase)

The work on operating the database (add, delete, check, change) is all in this category.

ExecSQL (sql)

Execute the SQL statement, using this method + SQL statement can be very convenient to add, delete, query and modify

In addition, Android also provides merit and fault methods to add, delete, query and change.

Long insert (TABLE_NAME, null, contentValues) add record

Int delete (TABLE_NAME, where, whereValue) delete records

Int update (TABLE_NAME, contentValues, where, whereValue) update record

Cursor query (TABLE_NAME, null, null) query records

In addition, there are many methods, such as: beginTransaction () to start a transaction, endTransaction () to end a transaction. If you are interested, you can watch api for yourself, so I won't dwell on it here.

3. Cursor (android.database.Cursor)

Cursor (interface), are you familiar with this? there are many methods in Cursor, and the commonly used ones are:

Boolean moveToPosition (position) moves the pointer to a record

GetColumnIndex (Contacts.People.NAME) gets id by column name

Int getCount () gets the total number of records

Boolean requery () re-query

Whether the boolean isAfterLast () pointer is at the end

Boolean isBeforeFirst () is the start position

Whether boolean isFirst () is the first record

Whether boolean isLast () is the last record

Boolean moveToFirst (), boolean moveToLast (), boolean moveToNext () and moveToPosition (position)

4. SimpleCursorAdapter (android.widget.SimpleCursorAdapter)

You may wonder, as I said before, that database operations are all under the database and database.sqlite packages. Why put an Adapter here? if you have used Android's SQLite3, you must know.

This is because our operations on the database are often associated with lists

Friends often make mistakes here, but it's actually very simple.

SimpleCursorAdapter adapter = new SimpleCursorAdapter (

This

R.layout.list

MyCursor

New String [] {DB.TEXT1,DB. TEXT2}

New int [] {R.id.list1J R.id.listText2})

My.setAdapter (adapter)

There are a total of 5 parameters, as follows:

Parameter 1:Content

Parameter 2: layout

Parameter 3:Cursor cursor object

Parameter 4: the displayed field, passed in String []

Parameter 5: displays the component used by the field, passing in int [], which is the id of the TextView component in the array

At this point, the operation on the database is over, but so far I have only done the translation work, some students may not have mastered, rest assured, let's sort things out along the normal development ideas!

The front is just to popularize friends who haven't done it before. here's what you really need!

First, write a class that inherits SQLiteOpenHelpe

Public class DatabaseHelper extends SQLiteOpenHelper

Construction method:

DatabaseHelper (Context context) {

Super (context, DATABASE_NAME, null, DATABASE_VERSION)

}

The operation of writing and creating tables in the onCreate method

Public void onCreate (SQLiteDatabase db) {

String sql = "CREATE TABLE tb_test (_ id INTEGER DEFAULT'1' NOT NULL PRIMARY KEY AUTOINCREMENT,class_jb TEXT NOT NULL,class_ysbj TEXT NOT NULL,title TEXT NOT NULL,content_ysbj TEXT NOT NULL)"

Db.execSQL (sql); / / exception capture is required

}

Delete the existing table in the onUpgrade method, and then manually call onCtreate to create the table

Public void onUpgrade (SQLiteDatabase db, int oldVersion, int newVersion) {

String sql = "drop table" + tbname

Db.execSQL (sql)

OnCreate (db)

}

For the methods of adding, deleting, querying and changing tables, the methods provided by SQLiteOpenHelper are used here, and they can also be implemented with sql statements. They are all the same.

When it comes to getting readable / writable SQLiteDatabase, I don't have to say that you should think that only lookups will use readable SQLiteDatabase.

/ * *

* add data

, /

Public long insert (String tname, int tage, String ttel) {

SQLiteDatabase db= getWritableDatabase (); / / get writable SQLiteDatabase object

/ / ContentValues is similar to map in that it stores key-value pairs

ContentValues contentValues = new ContentValues ()

ContentValues.put ("tname", tname)

ContentValues.put ("tage", tage)

ContentValues.put ("ttel", ttel)

Return db.insert (tbname, null, contentValues)

}

/ * *

* Delete records

* @ param _ id

, /

Public void delete (String _ id) {

SQLiteDatabase db= getWritableDatabase ()

Db.delete (tbname

"_ id=?"

New String [] {_ id})

}

/ * *

* update the record, very similar to the inserted one

, /

Public void update (String _ id,String tname, int tage, String ttel) {

SQLiteDatabase db= getWritableDatabase ()

ContentValues contentValues = new ContentValues ()

ContentValues.put ("tname", tname)

ContentValues.put ("tage", tage)

ContentValues.put ("ttel", ttel)

Db.update (tbname, contentValues

"_ id=?"

New String [] {_ id})

}

/ * *

* query all data

* @ return Cursor

, /

Public Cursor select () {

SQLiteDatabase db = getReadableDatabase ()

Return db.query (

Tbname

New String [] {"_ id", "tname", "tage", "ttel", "taddr"}

Null

Null, "_ id desc")

}

There are a lot of parameters about the db.query method. In order to prevent you from messing up, I'll say a few words briefly.

Parameter 1: table name

Parameter 2: returns the column information contained in the data. The String array contains all the column names.

Parameter 3: it is equivalent to the content written after where in the where,sql in sql, for example: tage >?

Parameter 4: what if you write it in parameter 3? Know why I wrote tage >? Right), this is the replacement? The value of the above example: new String [] {"30"}

Parameter 5: grouping. Do not explain. Pass null if you do not want to group.

Parameter 6:having. If you can't remember, look at SQL.

Parameter 7:orderBy sorting

So far, you have completed the most first steps! Let's take a look at what classes are used:

SQLiteOpenHelper we inherit the use of

SQLiteDatabase add, delete, check and change can not be separated from it, even if you directly use SQL statements, you also need to use execSQL (sql)

Second, here is nothing more than the call to the DatabaseHelper class definition method, there is nothing to say, but I would like to nag a few more words about the query

The result of Android query is returned in the form of Cursor

Cursor = sqLiteHelper.select (); / / is it very simple?

The queried cursor is usually displayed in the listView, which requires the use of the SimpleCursorAdapter just mentioned

SimpleCursorAdapter adapter = new SimpleCursorAdapter (

This

R.layout.list_row

Cursor

New String [] {"tname", "ttel"}

New int [] {R.id.TextView01,R.id.TextView02}

);

On how to connect to the database in Android to share here, I hope that the above content can be of some help to you, can learn more knowledge. If you think the article is good, you can share it for more people to see.

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