Android context provider DB更新

本文主要是介绍Android context provider DB更新，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

實際測試

當 new MyDBHlper時,會自動判斷,帶入的 version是不是跟之前的一樣,如果不一樣,就會先執行 MyDBHlper的onUpgrade

執行順序為

MyContentProvider: onCreate:
MyDBHlper: onUpgrade: oldVersion:1newVersion:2
MyDBHlper: onCreate:

public class MyContentProvider extends ContentProvider {@Overridepublic boolean onCreate() {Log.d(Tag, "onCreate: ");// MyDBHlper dbHper = new MyDBHlper(getContext(), DBname, null, 1);//FIXME:test version changeMyDBHlper dbHper = new MyDBHlper(getContext(), DBname, null, 2);MyDB = dbHper.getWritableDatabase();return true;}
}public class MyDBHlper extends SQLiteOpenHelper {@Overridepublic void onCreate(SQLiteDatabase db) {Log.d(Tag, "onCreate: ");db.execSQL(crTBsql);db.execSQL(initDBDate);}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {Log.d(Tag, "onUpgrade: oldVersion:" + oldVersion + "newVersion:" + newVersion);db.execSQL("DROP TABLE IF EXISTS " + TBname);onCreate(db);}
}

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轉載自http://mrraybox.blogspot.tw/2017/01/android-sqlite-onupgrade.html

本篇主要是示範：
1. 說明onUpgrade何時會啟用。
2. 示範如何使用onUpgrade。
3. 觀察onUpgrade使用後的前後差異。

相信開始接觸SQLite的大家都知道SQLiteOpenHelper中有一個方法叫onUpgrade，但是這個方法是做什麼用的呢？首先我們知道onCreate是在Android載入時，找不到對應的資料庫資料，就會觸發的一個方法。而onUpgrade呢，則是在資料庫的結構有所改變時，才會觸發的一個方法。

舉例來說，假如我在一月時，寫了一個App給其他人使用，在二月時，因改版需求，所以需要新增或刪減資料表的欄位。但是此時，那些使用我們所寫的App的用戶們，在這段期間已經儲存許多資料了。為了保存用戶舊的資料，此時我們就需要運用到onUpgrade來修改我們資料表的結構。

首先這裡示範我們一開始所寫的App。首先Layout部分的配置。
File Name：activity_main.xml

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent" ><LinearLayoutandroid:layout_width="match_parent"android:layout_height="match_parent"android:orientation="vertical" ><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:orientation="horizontal" ><Buttonandroid:id="@+id/btn_new"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="新增" /><Buttonandroid:id="@+id/btn_delete"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="刪除" /></LinearLayout><LinearLayoutandroid:layout_width="match_parent"android:layout_height="wrap_content"android:gravity="right"android:orientation="horizontal" ><EditTextandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:hint="ID"android:id="@+id/edt1"android:layout_weight="1" /><EditTextandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:hint="Row1"android:id="@+id/edt2"android:layout_weight="1" /><EditTextandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:hint="Row2"android:id="@+id/edt3"android:layout_weight="1" /><Buttonandroid:id="@+id/btn_alter"android:layout_width="wrap_content"android:layout_height="wrap_content"android:text="修改" /></LinearLayout><TextViewandroid:layout_width="wrap_content"android:layout_height="wrap_content"android:text="txt"android:id="@+id/txt"/></LinearLayout></ScrollView>

File Name：MainActivity

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;public class MainActivity extends AppCompatActivity implements View.OnClickListener {private Button btnNew, btnDel, btnAlt;private EditText edtID, edtRow1, edtRow2;private TextView txt;private MyHelper helper;private SQLiteDatabase db;private Cursor c;private String result;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);btnNew = (Button) this.findViewById(R.id.btn_new);btnDel = (Button) this.findViewById(R.id.btn_delete); btnAlt = (Button) this.findViewById(R.id.btn_alter);edtID = (EditText) this.findViewById(R.id.edt1);edtRow1 = (EditText) this.findViewById(R.id.edt2);edtRow2 = (EditText) this.findViewById(R.id.edt3);txt = (TextView) this.findViewById(R.id.txt);btnNew.setOnClickListener(this);btnDel.setOnClickListener(this);btnAlt.setOnClickListener(this);helper = new MyHelper(this, "dbname", null, 1);db = helper.getWritableDatabase();queryDB();}private void queryDB() {c = db.query("tablename", null, null, null, null, null, null);result="";for(int i=0; i<c.getColumnCount();i++){result+=c.getColumnName(i)+", ";}result+="\n";while (c.moveToNext()) {result += c.getString(c.getColumnIndex("_id")) + ", "+c.getString(c.getColumnIndex("row1")) + ", "+c.getString(c.getColumnIndex("row2")) +"\n";}txt.setText(result);}@Overridepublic void onClick(View view) {String id = edtID.getText().toString();ContentValues values = new ContentValues();switch (view.getId()){case R.id.btn_new:values.put("row1", "Row1");values.put("row2", "Row2");db.insert("tablename", null, values);queryDB();break;case R.id.btn_delete:db.delete("tablename", "_id="+id,null);queryDB();break;case R.id.btn_alter:String row1 = edtRow1.getText().toString();String row2 = edtRow2.getText().toString();values.put("row1", row1);values.put("row2", row2);db.update("tablename", values, "_id=" + id, null);queryDB();break;}}@Overridepublic void finish() {c.close();db.close();super.finish();}
}

File Name：MyHelper

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;public class MyHelper extends SQLiteOpenHelper {private String createTab;private String tableName = "tablename";public MyHelper(Context context, String db_name, SQLiteDatabase.CursorFactory factory, int db_version) {super(context, db_name, factory, db_version);}@Overridepublic void onCreate(SQLiteDatabase db) {createTab = "create table "+ tableName +" (_id integer primary key AUTOINCREMENT, row1 text, row2 text)";db.execSQL(createTab);}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {}
}

在用戶新增完資料後，就會變成下面這樣。

接著是我們改版後的程式碼。
File Name：MainActivity

import android.content.ContentValues;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;public class MainActivity extends AppCompatActivity implements View.OnClickListener {private Button btnNew, btnDel, btnAlt;private EditText edtID, edtRow1, edtRow2;private TextView txt;private MyHelper helper;private SQLiteDatabase db;private Cursor c;private String result;@Overrideprotected void onCreate(Bundle savedInstanceState) {super.onCreate(savedInstanceState);setContentView(R.layout.activity_main);btnNew = (Button) this.findViewById(R.id.btn_new);btnDel = (Button) this.findViewById(R.id.btn_delete);btnAlt = (Button) this.findViewById(R.id.btn_alter);edtID = (EditText) this.findViewById(R.id.edt1);edtRow1 = (EditText) this.findViewById(R.id.edt2);edtRow2 = (EditText) this.findViewById(R.id.edt3);txt = (TextView) this.findViewById(R.id.txt);btnNew.setOnClickListener(this);btnDel.setOnClickListener(this);btnAlt.setOnClickListener(this);helper = new MyHelper(this, "dbname", null, 2);db = helper.getWritableDatabase();queryDB();}private void queryDB() {c = db.query("tablename", null, null, null, null, null, null);result="";for(int i=0; i<c.getColumnCount();i++){result+=c.getColumnName(i)+", ";}result+="\n";while (c.moveToNext()) {result += c.getString(c.getColumnIndex("_id")) + ", "+c.getString(c.getColumnIndex("row1")) + ", "+c.getString(c.getColumnIndex("row2")) +"\n";}txt.setText(result);}@Overridepublic void onClick(View view) {String id = edtID.getText().toString();ContentValues values = new ContentValues();switch (view.getId()){case R.id.btn_new:values.put("row1", "Row1");values.put("row2", "Row2");db.insert("tablename", null, values);queryDB();break;case R.id.btn_delete:db.delete("tablename", "_id="+id,null);queryDB();break;case R.id.btn_alter:String row1 = edtRow1.getText().toString();String row2 = edtRow2.getText().toString();values.put("row1", row1);values.put("row2", row2);db.update("tablename", values, "_id=" + id, null);queryDB();break;}}@Overridepublic void finish() {c.close();db.close();super.finish();}
}

File Name：MyHelper

import android.content.Context;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;public class MyHelper extends SQLiteOpenHelper {private String createTab;private String tableName = "tablename";public MyHelper(Context context, String db_name, SQLiteDatabase.CursorFactory factory, int db_version) {super(context, db_name, factory, db_version);}@Overridepublic void onCreate(SQLiteDatabase db) {   createTab = "create table "+ tableName +" (_id integer primary key AUTOINCREMENT, row1 text, row2 text, row3 text)";db.execSQL(createTab);}@Overridepublic void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {if(oldVersion == 1 && newVersion == 2){//Adding a row3String sql = "alter table "+ tableName +" add row3 text";db.execSQL(sql);}}
}