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Android备考01 黑马76期-day03 操作数据库

發布時間：2024/3/12 Android 29 豆豆

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數據庫創建以及原始方式操作數據庫

activity_main.xml

MyOpenHelper.java

package com.example.sqlite2;import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteOpenHelper;public class MyOpenHelper extends SQLiteOpenHelper {/*** @param context 上下文* @param name 數據庫的名字* @param factory 創建cursor對象(就是游標也即結果集)* @param version 數據庫的版本* */public MyOpenHelper(Context context) {super(context, "itheima.db", null, 3);}/*** 數據庫第一創建時調用* 特別適合做表格結構的初始化 * 那么可得此方法就是寫創建表的sql語句的*/@Overridepublic void onCreate(SQLiteDatabase db) {//1. sqlite的id一般寫成 "_id"//2. 數據類型統一為String 寫了和沒寫一樣為何和數據庫程序員融洽對接以及增加可讀性企業還是要求規范寫db.execSQL("create table info(_id integer primary key autoincrement,name varchar(20))");}/*** 數據庫版本升級時調用* 適合于更新表結構*/@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {db.execSQL("alter table info add phone varchar(20)");}}

MainActivity.java

package com.example.sqlite2;import android.os.Bundle; import android.app.Activity; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.view.Menu; import android.view.View; import android.widget.Toast;public class MainActivity extends Activity {private MyOpenHelper helper;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);helper = new MyOpenHelper(getApplicationContext());//打開或者創建數據庫第一次創建//SQLiteDatabase writableDatabase = helper.getWritableDatabase();//打開或者創建數據庫第一次創建若磁盤滿返回一個只讀的 // SQLiteDatabase readableDatabase = helper.getReadableDatabase();}//點擊按鈕增加一條記錄public void click1(View v){//[1]獲取數據庫對象SQLiteDatabase db = helper.getWritableDatabase();//[2]執行增加一條記錄的sql語句db.execSQL("insert into info(name,phone) values(?,?);",new Object[]{"張三","14575651"});//[3]數據庫用完關閉db.close();}//刪除public void click2(View v){SQLiteDatabase db = helper.getWritableDatabase();db.execSQL("delete from info where name=?;", new Object[]{"張三"});db.close();}//更新public void click3(View v){SQLiteDatabase db = helper.getWritableDatabase();db.execSQL("update info set phone=? where name=?;", new Object[]{"110120","張三"});db.close();}//查詢public void click4(View v){SQLiteDatabase db = helper.getReadableDatabase();//獲取游標即結果集Cursor cursor = db.rawQuery("select * from info;", null);if(cursor.getCount()<=0){Toast.makeText(this, "數據庫空", 0).show();return;}StringBuffer ans=new StringBuffer();//一行一行獲取數據while(cursor.moveToNext()){//編號重0開始 0是id不取String name = cursor.getString(1);String phone = cursor.getString(2);ans.append("\nname:"+name+" phone:"+phone);}Toast.makeText(this,ans, 0).show();}}

小結1

容易進行多表查詢

命令行訪問sqlite數據庫

adb shell
cd data/data
ls
cd com.example.sqlite2
ls
cd databases
ls
sqlite3 itheima.db
select * from info;

提示：sqlite3: not found
需要下載安裝sqlite3工具

★改變dos窗口的編碼（解決某些亂碼）

改為gbk:? chcp 936

改為u8: chcp 65001

?

使用api進行crud

有諸多好處，但寫起來特別復雜，不如直接寫sql語句

MainActivity.java

package com.example.sqlite2;import android.app.Activity; import android.content.ContentValues; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.os.Bundle; import android.view.View; import android.widget.Toast;import com.example.crud.R;public class MainActivity extends Activity {private MyOpenHelper helper;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);helper = new MyOpenHelper(getApplicationContext());//打開或者創建數據庫第一次創建//SQLiteDatabase writableDatabase = helper.getWritableDatabase();//打開或者創建數據庫第一次創建若磁盤滿返回一個只讀的 // SQLiteDatabase readableDatabase = helper.getReadableDatabase();}//點擊按鈕增加一條記錄public void click1(View v){//[1]獲取數據庫對象SQLiteDatabase db = helper.getWritableDatabase();//[2]執行增加一條記錄的sql語句//db.execSQL("insert into info(name,phone) values(?,?);",new Object[]{"張三","14575651"});/*** db.insert(table, nullColumnHack, values)* * table:表名* values：ContentValues類內封裝一個map key:列名 value:插入的值*/ContentValues values=new ContentValues();values.put("name", "王五");values.put("phone", "110");//返回值為插入新行的idlong insert = db.insert("info", null, values);//insert底層就在封裝sql語句//[3]數據庫用完關閉db.close();if(insert>0){Toast.makeText(getApplicationContext(), "添加成功!", 0).show();}else{Toast.makeText(getApplicationContext(), "添加失敗!", 0).show();}}//刪除public void click2(View v){SQLiteDatabase db = helper.getWritableDatabase();//db.execSQL("delete from info where name=?;", new Object[]{"張三"});/*** db.delete(table, whereClause, whereArgs)* * table:所刪表名* whereClause：刪除條件* whereArgs：參數注意是new String[]{}* * 返回值：影響的行數*/int delete = db.delete("info", "name=?", new String[]{"王五"});db.close();Toast.makeText(getApplicationContext(), "刪除了"+delete+"行！", 0).show();}//更新public void click3(View v){SQLiteDatabase db = helper.getWritableDatabase();//db.execSQL("update info set phone=? where name=?;", new Object[]{"110120","張三"});/*** db.update(table, values, whereClause, whereArgs)* * table:表名* values：ContentValues key:修改的列名 values:新的列值* whereClause:條件* whereArgs：參數* 返回值：更新了多少行*/ContentValues values=new ContentValues();values.put("phone", "114"); int update = db.update("info", values, "name=?", new String[]{"王五"});db.close();Toast.makeText(getApplicationContext(), "更新了"+update+"行！", 0).show();}//查詢public void click4(View v){SQLiteDatabase db = helper.getReadableDatabase();//獲取游標即結果集//Cursor cursor = db.rawQuery("select * from info;", null);/*** db.query(table, columns, selection, selectionArgs, groupBy, having, orderBy)* 見名識義* columns：String[] 要查詢的列名 null代表查詢所有* selection: 查詢條件* selectionArgs: 查詢參數* groupBy：分組條件* having：過濾條件* orderBy：排序條件* * eg:db.query("info",new String[]{"phone"},"name=?",new String[]{"王五"},null,null,null);*/Cursor cursor = db.query("info",new String[]{"phone"},"name=?",new String[]{"王五"},null,null,null);if(cursor.getCount()<=0){Toast.makeText(this, "數據庫空", 0).show();return;}StringBuffer ans=new StringBuffer();//一行一行獲取數據while(cursor.moveToNext()){//編號重0開始注意此時只查詢一列 phone就是0String phone = cursor.getString(0);ans.append("\nphone:"+phone);}Toast.makeText(this,ans, 0).show();}}

Android事務模板（轉賬）

activity_main.xml

MyOpenHelper.java

package com.example.transaction;import android.content.Context; import android.database.sqlite.SQLiteDatabase; import android.database.sqlite.SQLiteDatabase.CursorFactory; import android.database.sqlite.SQLiteOpenHelper;public class MyOpenHelper extends SQLiteOpenHelper {public MyOpenHelper(Context context) {super(context, "Account", null, 1);}@Overridepublic void onCreate(SQLiteDatabase db) {db.execSQL("create table info(_id integer primary key autoincrement,name varchar(20),phone varchar(20),account varchar(20))");db.execSQL("insert into info(name,phone,account) values('張三','110','3000')");db.execSQL("insert into info(name,phone,account) values('李四','120','3000')");}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}}

MainActivity.java

package com.example.transaction;import android.os.Bundle; import android.app.Activity; import android.database.Cursor; import android.database.sqlite.SQLiteDatabase; import android.view.Menu; import android.view.View; import android.widget.Toast;public class MainActivity extends Activity {private SQLiteDatabase db;private SQLiteDatabase db2;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);MyOpenHelper myOpenHelper = new MyOpenHelper(getApplicationContext());db = myOpenHelper.getWritableDatabase();db2 = myOpenHelper.getReadableDatabase();}public void click(View v) {db.beginTransaction();//開啟事務try {db.execSQL("update info set account=account-100 where name=?",new String[] { "張三" });int i=1/0;db.execSQL("update info set account=account+100 where name=?",new String[] { "李四" });// 未發生異常會執行到此行，也就會幫你提交// 發生異常就不會執行到此行，自動回滾db.setTransactionSuccessful();Toast.makeText(getApplicationContext(), "轉賬成功!", 0).show();} catch (Exception e) {Toast.makeText(getApplicationContext(), "服務器忙，請稍后再試試~~", 0).show();} finally {db.endTransaction();//關閉事務}}//查詢所有public void click2(View v) {Cursor cursor = db2.rawQuery("select name,phone,account from info",null);StringBuffer sb = new StringBuffer();while (cursor.moveToNext()) {sb.append(cursor.getString(0) + "\t" + cursor.getString(1) + "\t"+ cursor.getString(2) + "\n");}Toast.makeText(getApplicationContext(), sb, 0).show();} }

ListView控件入門

activity_main.xml里寫一個文件，MainActivity.java里用java代碼布局顯示內容

activity_main.xml

MainActivity.java

package com.example.listview;import android.os.Bundle; import android.app.Activity; import android.view.Menu; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.ListView; import android.widget.TextView;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//[1]找到關心的控間ListView lv = (ListView) findViewById(R.id.lv);//[2]顯示數據 textview和其他普通控件有點區別它的數據來源于數據適配器lv.setAdapter(new MyListAdapter());}/*** 初始化布局代碼* @author Administrator**///[3] 定義listview的數據適配器private class MyListAdapter extends BaseAdapter{//一共顯示多少條目@Overridepublic int getCount() {return 100;}//返回指定position(重0開始)處的對象用默認即可@Overridepublic Object getItem(int position) {return null;}//返回position位置對應的id@Overridepublic long getItemId(int position) {return 0;}/*** 獲取一個view 用來顯示listview的數據會作為listview的一個條目出現* 每條顯示多少*/@Overridepublic View getView(int position, View convertView, ViewGroup parent) {TextView tv=new TextView(MainActivity.this);tv.setText("哈哈哈"+position);return tv;}} }

ListView優化

布局加滾動條

items采用復用技術，使得大大節省內存，也絕對不會內存溢出

activity_main.xml

MainActivity.java

package com.example.listview;import android.os.Bundle; import android.app.Activity; import android.view.Menu; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.ListView; import android.widget.TextView;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);//[1]找到關心的控間ListView lv = (ListView) findViewById(R.id.lv);//[2]顯示數據 textview和其他普通控件有點區別它的數據來源于數據適配器lv.setAdapter(new MyListAdapter());}/*** 初始化布局代碼* @author Administrator**///[3] 定義listview的數據適配器private class MyListAdapter extends BaseAdapter{//一共顯示多少條目@Overridepublic int getCount() {return 1000;}//返回指定position(重0開始)處的對象用默認即可@Overridepublic Object getItem(int position) {return null;}//返回position位置對應的id@Overridepublic long getItemId(int position) {return 0;}/*** 獲取一個view 用來顯示listview的數據會作為listview的一個條目出現* 每條顯示多少*/@Overridepublic View getView(int position, View convertView, ViewGroup parent) { // System.out.println("listview"+position);//說明界面上顯示一條才調用一次本方法 // TextView tv=new TextView(MainActivity.this);//每次都new 內存不夠快速拖拽，前面的沒來得及釋放就會內存溢出TextView tv;//簡簡單單的判斷保證快速滑動也不會卡死復用使得只用創建一屏能顯示的條目數個tv就行了if(convertView==null){tv=new TextView(MainActivity.this);System.out.println("創建view對象---"+position);}else{System.out.println("復用歷史緩存對象---"+position);tv=(TextView) convertView;}tv.setText("哈哈哈"+position);return tv;}} }

奇怪現象

listview布局中的android:layout_height="match_parent"? ?都寫match_parent? 不要用wrap_content

都這么寫：

<ListViewandroid:id="@+id/lv"android:layout_width="match_parent"android:layout_height="match_parent"/>

包裹內容就無法確定高度，也就無法準確計算出一屏一共需要new出多少個items就會多次嘗試最終new出很多多余的item,效率會低點

listview練習復雜布局

activity_main.xml

item.xml

<?xml version="1.0" encoding="utf-8"?> <RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_marginTop="10dp"android:layout_width="match_parent"android:layout_height="wrap_content" ><ImageViewandroid:id="@+id/iv_icon"android:layout_width="wrap_content"android:layout_height="wrap_content"android:src="@drawable/pci" /><TextView android:id="@+id/iv_title"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_toRightOf="@+id/iv_icon"android:singleLine="true"android:ellipsize="end"android:textColor="#000000"android:textSize="20sp"android:text="畢業生拒絕年薪300萬工作選擇年薪200萬的華為"/><TextView android:id="@+id/iv_messgae"android:layout_width="match_parent"android:layout_height="wrap_content"android:layout_marginTop="5dp"android:layout_toRightOf="@+id/iv_icon"android:layout_below="@+id/iv_title"android:textColor="#999999"android:textSize="15sp"android:text="今天，剛畢業就年薪200萬”的話題沖上熱搜！他是誰？"/></RelativeLayout>

MainActivity.java

package com.example.listviewLX;import android.os.Bundle; import android.app.Activity; import android.view.Menu; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.LinearLayout; import android.widget.ListView;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);// [1]找到關心的控件ListView lv=(ListView) findViewById(R.id.lv);//[2]設置適配器布局lv.setAdapter(new MyAdapter());}public class MyAdapter extends BaseAdapter{@Overridepublic int getCount() {return 1000;}@Overridepublic Object getItem(int position) {return null;}@Overridepublic long getItemId(int position) {return 0;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {//[1]想辦法將自定義的布局轉換為一個viewView view;if(convertView==null){/*** View.inflate(context, resource, root)* * 創建新的view對象通過打氣筒inflate將一個xml布局轉換為一個view* resource就是xml文件通過R.layout找到* root:ViewGroup類型 LinearLayout,reaLayout都繼承自ViewGroup，這種類型可以有自己的孩子* root即用來指定默認的父親此處只為了轉換為view,故用不到*/view = View.inflate(getApplicationContext(), R.layout.item, null);}else{//復用歷史緩存對象view=convertView;}return view;}} }

獲取打氣筒各種方法

3種方法，第一種最簡單，第三種最常用

// 獲取打氣筒方法一 view = View.inflate(getApplicationContext(), R.layout.item,null);// 獲取打氣筒方法二 view = LayoutInflater.from(getApplicationContext()).inflate(R.layout.item, null);//獲取打氣筒方法三 LayoutInflater layoutInflater=(LayoutInflater)getSystemService(LAYOUT_INFLATER_SERVICE); view = layoutInflater.inflate(R.layout.item, null);

MainActivity.java

package com.example.listviewLX;import android.os.Bundle; import android.app.Activity; import android.view.LayoutInflater; import android.view.Menu; import android.view.View; import android.view.ViewGroup; import android.widget.BaseAdapter; import android.widget.LinearLayout; import android.widget.ListView;public class MainActivity extends Activity {@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);// [1]找到關心的控件ListView lv = (ListView) findViewById(R.id.lv);// [2]設置適配器布局lv.setAdapter(new MyAdapter());}public class MyAdapter extends BaseAdapter {@Overridepublic int getCount() {return 1000;}@Overridepublic Object getItem(int position) {return null;}@Overridepublic long getItemId(int position) {return 0;}@Overridepublic View getView(int position, View convertView, ViewGroup parent) {// [1]想辦法將自定義的布局轉換為一個viewView view;if (convertView == null) {/*** View.inflate(context, resource, root)* * 創建新的view對象通過打氣筒inflate將一個xml布局轉換為一個view resource就是xml文件* 通過R.layout找到 root:ViewGroup類型* LinearLayout,reaLayout都繼承自ViewGroup，這種類型可以有自己的孩子* root即用來指定默認的父親此處只為了轉換為view,故用不到*/// 獲取打氣筒方法一// view = View.inflate(getApplicationContext(), R.layout.item,null);// 獲取打氣筒方法二//view = LayoutInflater.from(getApplicationContext()).inflate(R.layout.item, null);//獲取打氣筒方法三LayoutInflater layoutInflater = (LayoutInflater) getSystemService(LAYOUT_INFLATER_SERVICE);view = layoutInflater.inflate(R.layout.item, null);} else {// 復用歷史緩存對象view = convertView;}return view;}} }

每項顯示單一數據（textview）的listview適配器 arrayAdapter

activity_main.xml

item.xml

<?xml version="1.0" encoding="utf-8"?> <TextView xmlns:android="http://schemas.android.com/apk/res/android"android:id="@+id/textView1"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="TextView" />

item2.xml

<?xml version="1.0" encoding="utf-8"?> <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"android:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical" ><TextViewandroid:id="@+id/tv2"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="TextView" /></LinearLayout>

MainActivity.java

package com.example.arrayadapter;import android.os.Bundle; import android.app.Activity; import android.view.Menu; import android.view.View; import android.widget.ArrayAdapter; import android.widget.ListView;public class MainActivity extends Activity {String objects[]={"天河","紫英","夢璃","菱紗","天青","玄霄","夙玉"};@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);// [1]找到關心的控件ListView lv = (ListView) findViewById(R.id.lv);//顯式單一文本信息時不必要用basedaptor 用arrayadptor即可//[2]創建一個arrayAdapter (注意此處的adapter的作用都只是專門顯式item到listview上)//方法1：注意自定義的R.layout.item只能是個textview 外面不能包什么布局//ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.item, objects);//方法2：自定義的R.layout.item2里可以有布局包裹了，但是一定要給定義的textview定義id 需要特別指定ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, R.layout.item2, R.id.tv2, objects);//[3]設置數據適配器lv.setAdapter(adapter);} }

總結

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