Android app development-data storage and Interface display (ii) (re-plate)

SQLite database

// Custom class myopenhelper inherit from Sqliteopenhelper New null, 1); // Obtain the database object, if the database does not exist, first create the database, then obtain it, if it exists, directly Sqlitedatabase db = Oh.getwritabledatabase ();

Getwritabledatabase (): Open the database corresponding Sqlitedatabase object in read and write mode, error when disk space is insufficient

Getreadabledatabase (): The function first calls Getwritabledatabase (), if there is insufficient disk space, returns an open failure, and then opens the corresponding Sqlitedatabase object for the database in a read-only manner

Create a table when you create a database

 Public void onCreate (Sqlitedatabase db) {    //  TODO auto-generated method stub    db.execsql (" CREATE TABLE person (_id Integer primary key autoincrement, name Char (TEN), Phone char (), Money Integer) ");

Database additions and deletions change

SQL statements

 　　 Insert  intoPerson (name, phone, Money)Values('Zhang San','159874611', -); Delete  fromPersonwhereName= 'John Doe'  and_id= 4; UpdatePersonSet  Money = 6000 whereName= 'John Doe'; SelectName, phone fromPersonwhereName= 'Zhang San';

Execute SQL statements to implement additions and deletions

New object[]{"Zhang San", 15987461, 75000}); // Insert New string[]{"Zhang San"});    // Find

This method is called before the test method executes

protected void throws Exception {    super. SetUp ();     // get the virtual context object    New null, 1);}

Use API to implement additions and deletions

Insert

// encapsulates the data to be inserted into a Contentvalues object in the form of a key-value pair New contentvalues (); Cv.put ("name", "Liu Can"), Cv.put ("Phone", 1651646); Cv.put ("Money", 3500  ); Long　　null, CV); // The return value is the primary key of the inserted row and returns 1 if an error occurs

Delete

int New string[]{"1", "Zhang San"});    // The return value is the number of rows deleted

Modify

New contentvalues (); Cv.put ("Money", 25000); int New string[]{"Zhao Si"});    // The return value is the primary key of the modified row and returns 1 if an error occurs

Find

//arg2: The field to query//arg3: Query Criteria//Arg4: Placeholder for populating query criteriaCursor cs = db.query ("Person",Newstring[]{"Name", "Money"}, "name =?",Newstring[]{"Zhang San"},NULL,NULL,NULL); while(Cs.movetonext ()) {//gets the index value of the specified columnString name = cs.getstring (Cs.getcolumnindex ("name")); String Money= Cs.getstring (Cs.getcolumnindex ("Money")); SYSTEM.OUT.PRINTLN (Name+ ";" +Money );}

Transaction

Ensure that multiple SQL statements either succeed at the same time or fail at the same time

Most common case: bank transfer

Transaction API

Try {    // open transaction     db.begintransaction ();    ...........     // SET Transaction Execution Success finally {    // Close transaction     / /       If the transaction execution succeeds at this time, the SQL statement takes effect, otherwise it does not take effect     db.endtransaction ();}

Display data from the database to the screen

1. Arbitrarily inserting some data

2. Define Business Bean:Person.java

3. Read all data from the database

Cursor cs = db.query ("Person",NULL,NULL,NULL,NULL,NULL,NULL); while(Cs.movetonext ()) {String name= Cs.getstring (Cs.getcolumnindex ("name")); String Phone= Cs.getstring (Cs.getcolumnindex ("Phone")); String Money= Cs.getstring (Cs.getcolumnindex ("Money")); //encapsulates the read data into a person objectPerson p =NewPerson (name, phone, money); //Save the Person object to the collectionPeople.add (P);}

4. Display the data in the collection to the screen

LinearLayout ll =for(person p:people) {     // create TextView, each piece of data is displayed with a text box     New TextView (this);     Tv.settext (P.tostring ());      // Set the text box to the child node of LL      Ll.addview (TV);}

Paging Query

NULL NULL NULL NULL NULL null, "0, 10");

Listview

Lsitview used to display a line of items

MVC architecture

M:model model layer, the data to be displayed ———— people collection

V:view view layer, the user sees the interface ———— ListView

C:control control layer, manipulating how data is displayed ———— adapter object

Each entry is a View object

Baseadapter

Two methods that must be implemented

First one

// The system calls this method to learn how many data the model layer has  Public int GetCount () {    return  people.size ();}

A second

//The system calls this method to get the view object to display to the ListView//position: Is the position of the data in the collection for the Return view object PublicView GetView (intposition, View Convertview, ViewGroup parent) {System.out.println ("GetView method call" +position); TextView TV=NewTextView (mainactivity. This); //get the elements in the collectionPerson p =People.get (position);    Tv.settext (P.tostring ()); //return the TextView object and it will become the entry for the ListView.    returnTV;}

How many entries are displayed on the screen, how many times the GetView method will be called, and GetView will continue to be called when the screen is slid down, creating more view objects to display to the screen

　　Cache of Entries
When the entry is a screen, the system will cache the entry into memory, when the entry again into the screen, the system will re-call GetView when the cache entry as the Convertview parameter, but the incoming entry is not necessarily the previously cached entry, That is, it is possible for the system to pass the cache of any entry when it calls the GetView method to get the first entry

dialog box

OK Cancel dialog box

Create a Dialog builder object similar to Factory mode

New Builder (this);

Set the title and body

Builder.settitle ("Warning"); Builder.setmessage ("If you practice this work, you must first be self-palace");

Set OK and Cancel buttons

Builder.setpositivebutton ("Now self-palace",NewOnclicklistener () {@Override Public voidOnClick (Dialoginterface Dialog,intwhich) {        //TODO auto-generated Method StubToast.maketext (mainactivity. This, "Congratulations on your self-palace success, now program quit", 0). Show (); }}); Builder.setnegativebutton ("Next time,"NewOnclicklistener () {@Override Public voidOnClick (Dialoginterface Dialog,intwhich) {        //TODO auto-generated Method StubToast.maketext (mainactivity. This, "If not from the palace, must not succeed", 0). Show (); }});

Using the Builder to create a dialog box object

Alertdialog ad = builder.create (); Ad.show ();

Single-selection dialog box

New Builder (this); Builder.settitle ("Choose your Gender");

Define a radio option

Finalstring[] Items =Newstring[]{Male,         Female};//-1 means no one is selected by default//Click to listen to the guide package to pay attention to the wrong guideBuilder.setsinglechoiceitems (items,-1,NewOnclicklistener () {//dialog: A dialog box that triggers this method//which: Subscript for user-selected entry@Override Public voidOnClick (Dialoginterface Dialog,intwhich) {Toast.maketext (mainactivity). This, "You have selected" + Items[which], 0). Show (); //Close the dialog boxDialog.dismiss (); }});//You can display the dialog box directly with the builderBuilder.show ();

Multi-Select dialog box

New Builder (this); Builder.settitle ("Please select the person you think is handsome");

The option to define multiple selections, because you can select multiple, so you need a Boolean array to record which options are selected

Finalstring[] Items =Newstring[]{"Daniel Wu",        "Anna",        "Andy Lau",        "Louis Koo"};//only the first entry is selected by defaultFinal Boolean[] CheckedItems =New Boolean[]{        true,        false,        false,        false,};builder.setmultichoiceitems (items, CheckedItems,NewOnmultichoiceclicklistener () {//which: the user clicks on the subscript of the entry//isChecked: Used to determine whether the user clicked the entry is selected or canceled@Override Public voidOnClick (Dialoginterface Dialog,intWhich,BooleanisChecked) {Checkeditems[which]=isChecked; }});//set a OK buttonBuilder.setpositivebutton ("OK",NewOnclicklistener () {@Override Public voidOnClick (Dialoginterface Dialog,intwhich) {StringBuffer SB=NewStringBuffer ();  for(inti = 0;i < items.length; i++) {sb.append (Checkeditems[i]? Items[i] + "": ""); } toast.maketext (mainactivity. This, sb.tostring (), 0). Show (); }}); Builder.show ();

Android app development-data storage and Interface display (ii) (re-plate)