Android復習知識點

1.數據庫讀寫

首先新建一個數據庫工具類繼承自SQLiteOpenHelper，然后在構造方法中指定數據庫名稱

和版本號進行初始化。代碼如下：

MyDataBase.java

package chzu.csci.pwn.androidquiz;

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import android.content.ContentValues;

import android.content.Context;

import android.database.sqlite.SQLiteDatabase;

import android.database.sqlite.SQLiteOpenHelper;

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public class MyDataBase extends SQLiteOpenHelper {

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????private static final String DB_NAME="2017211808.db";

????private static final int DB_VERSION=1;

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????MyDataBase(Context context){

????????super(context,DB_NAME,null,DB_VERSION);

????}

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????@Override

????public void onCreate(SQLiteDatabase db) {

????????db.execSQL(//第一次運行時新建一個BANK表，并且插入初始數據

????????????????"CREATE TABLE BANK (_id INTEGER PRIMARY KEY AUTOINCREMENT,"

????????????????????????+"TYPE TEXT,"

????????????????????????+"QUESTION TEXT,"

????????????????????????+"ANSWER TEXT);"

????????);

????????insertBank(db,"架構","Android系統架構自底向上第二層是？");

????????insertBank(db,"編程","Android App開發支持編程語言包括？");

????????insertBank(db,"服務","綁定服務使用什么方法？");

????}

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????@Override

????public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {

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????}

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????private static void insertBank(SQLiteDatabase db,String type,String question){

????????ContentValues value=new ContentValues();

????????value.put("TYPE",type);

????????value.put("QUESTION",question);

????????long result=db.insert("BANK",null,value);

????}

}

1.插入數據

調用SQLiteDatabase類的insert方法即可，代碼如下，具體調用可以看上面的MyDataBase.java：

ContentValues value=new ContentValues();

value.put("TYPE",type);//字段名和值

value.put("QUESTION",question);//字段名和值

long result=db.insert("BANK",null,value);

2.刪除數據

調用SQLiteDatabase類的delete方法即可，代碼如下:

SQLiteOpenHelper helper=new MyDataBase(this);

try{

?????SQLiteDatabase db=helper.getWritableDatabase();

?????//刪除TYPE字段為"架構"的行

?????db.delete("BANK","TYPE=?",new String[]{"架構"});

?}catch (SQLException e){

?????Toast.makeText(this,"DataBase unavalibale",Toast.LENGTH_SHORT).show();

?}

3.修改數據

調用SQLiteDatabase類的update方法，傳入ContentValues對象即可，代碼如下:

SQLiteDatabase db=helper.getWritableDatabase();

ContentValues bankvalues=new ContentValues();

bankvalues.put("ANSWER",answer);//ANSWER為想要修改的字段名，answer為想要修改成的值

db.update("BANK",bankvalues,"_id=?",new String[]{Integer.toString(ID)});

4.查詢數據

調用SQLiteDatabase類的query方法，返回一個Cursor對象，類似于ResultSet結果集，

代碼如下：

SQLiteDatabase db=helper.getReadableDatabase();

cursor= db.query("BANK",new String[]{"_id","TYPE"},null,null,null,null,null);//相當于執行SQL語句SELECT _id,TYPE FROM BANK

加上查詢條件，代碼如下:

SQLiteDatabase db=helper.getReadableDatabase();

cursor=db.query("BANK",new String[]{"QUESTION","ANSWER"},"_id=?",

?????????new String[]{Integer.toString(ID)},null,null,null);

?????????/*相當于執行SQL語句SELECT QUESTION,ANSWER FROM BANK WHERE _id=ID*/ ???????

2.按鍵事件處理

public void onClickSave(View view){

? /*此處填寫點擊后的響應事件邏輯代碼，另外在視圖層對應的xml文件中相應按鈕的屬性設置android:onClick="onClickSave"*/ ??????

}

3.CursorAdapter(游標適配器)

通過findViewById方法獲取ListView組件，然后再調用db的query方法獲取數據庫中的內容，

返回值是一個Cursor游標對象，對SimpleCursorAdapter類進行構造后生成對象后，調用

ListView對象的setAdapter方法，進行適配器設置，即可在頁面中顯示數據庫內容。

/*listView為響應的ListView組件對象，cursor為查詢出的的游標對象，new String{"TYPE"}是在ListView中展示的內容

*/

SimpleCursorAdapter listAdapter=new SimpleCursorAdapter(this,android.R.layout.simple_list_item_1,

????????????????????cursor,new String[]{"TYPE"},new int[]{android.R.id.text1},0);

listView.setAdapter(listAdapter);

4.界面跳轉時傳遞數據

通過構造一個Intent對象，然后調用intent對象的putExtra方法存入數據，最后調

用startActivity方法啟動。

/*MainActivity是跳轉前的界面Activity，SecondActivity是跳轉的目標界面的Activity*/

Intent intent=new Intent(MainActivity.this,SecondActivity.class);

intent.putExtra("ID",(int)id);

startActivity(intent);

5.Toast會話

/*"DataBase unavalibale為顯示的內容，Toast.LENGTH_SHORT為會話持續時間，改為Toast.LENGTH_LONG可以延長會話持續時間*/

Toast.makeText(this,"DataBase unavalibale",Toast.LENGTH_SHORT).show();

6.音樂播放服務

通過綁定式服務即可實現，在res目錄下新建一個raw目錄，然后將音樂文件粘貼進該目錄，具體代碼如下:

MusicService.java

package chzu.csci.pwn.androidquiz;

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import android.app.Service;

import android.content.Intent;

import android.media.MediaPlayer;

import android.os.Binder;

import android.os.IBinder;

import android.util.Log;

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import androidx.annotation.Nullable;

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public class MusicService extends Service{

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????private MediaPlayer mediaPlayer;

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????//Service初始化時調用

????public void onCreate(){

????????super.onCreate();

????????mediaPlayer = MediaPlayer.create(this, R.raw.notice);//這里注意將音樂文件修改成自己的

????}

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????public class MusicBinder extends Binder{

????????MusicService getMusic(){

????????????return MusicService.this;

????????}

????}

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????private IBinder binder=new MusicBinder();

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????@Override

????public IBinder onBind(Intent intent) {

????????if(!mediaPlayer.isPlaying()){

????????????// 開始播放

????????????mediaPlayer.start();

????????????// 允許循環播放

????????????mediaPlayer.setLooping(true);

????????}

????????return binder;

????}

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????public boolean onUnbind(Intent intent) {

????????if(mediaPlayer.isPlaying()){

????????????mediaPlayer.stop();

????????}

????????return super.onUnbind(intent);

????}

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????@Override

????public void onDestroy() {

????????// TODO Auto-generated method stub

????????super.onDestroy();

????????//先停止 再釋放

????????if(mediaPlayer.isPlaying()){

????????????mediaPlayer.stop();

????????}

????????mediaPlayer.release();

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????}

????public MusicService() {

????}

}

onClickStart方法調用后播放音樂，onClickStop方法調用后停止播放，可以將方法與按鈕的onClick進行綁定，從而通過按鈕控制音樂開關。

MainActivity.java

/*導入類代碼省略*/

public class MainActivity extends AppCompatActivity {

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????/*無關代碼省略*/

????private MusicService musicService;

????private ServiceConnection connection;

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????@Override

????protected void onCreate(Bundle savedInstanceState) {

???????/*無關代碼省略*/

????????connection=new ServiceConnection() {

????????function(){ //KDJ指標http://www.fx61.com/faq/muniu/456.html

????????????@Override

????????????public void onServiceConnected(ComponentName name, IBinder service) {

????????????????MusicService.MusicBinder binder=(MusicService.MusicBinder)service;

????????????????musicService=binder.getMusic();

????????????}

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????????????@Override

????????????public void onServiceDisconnected(ComponentName name) { }

????????};

???????/*無關代碼省略*/

????}

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????/*無關代碼省略*/

????

????public void onClickStart(View view){

???????/*無關代碼省略*/

????????Intent intent = new Intent(this,MusicService.class);

????????bindService(intent,connection,BIND_AUTO_CREATE);

????}

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????public void onClickStop(View view){

??????/*無關代碼省略*/

???????unbindService(connection); ????

????}

}

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7.橫豎屏切換處理

主要就是將Activity的某些變量在Activity退出調用onSaveInstanceState時進行值儲存，然后在載入Activity調用onCreate方法時進行值讀取，相關代碼如下：

MainActivity.java

/*無關代碼已省略*/

public class MainActivity extends AppCompatActivity {

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????private boolean running=false;

????private int seconds=0;

????private boolean wasRunning=false;

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????@Override

????protected void onCreate(Bundle savedInstanceState) {

????????super.onCreate(savedInstanceState);

????????setContentView(R.layout.activity_main);

????????if(savedInstanceState!=null){

????????????seconds=savedInstanceState.getInt("seconds");

????????????running=savedInstanceState.getBoolean("running");

????????????wasRunning=savedInstanceState.getBoolean("wasRunning");

????????}

????}

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????@Override

????protected void onStop() {

????????super.onStop();

????????wasRunning=running;

????????running=false;

????}

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????@Override

????protected void onStart() {

????????super.onStart();

????????if(wasRunning){

????????????running=true;

????????}

????}

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????@Override

????public void onSaveInstanceState(Bundle outState) {

????????super.onSaveInstanceState(outState);

????????outState.putBoolean("running",running);

????????outState.putInt("seconds",seconds);

????????outState.putBoolean("running",wasRunning);

????}

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}

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8.線程

一些耗時操作可以用線程操作，以免堵塞。可以聲明一個內部類繼承自AsyncTask，然后

重寫其onPreExecute、doInBackground、onPostExecute方法。調用時調用該內部類對象

的execute方法即可，注意drinkId與AsyncTask<Integer,Void,Boolean>中的Integer相對應。

/*無關代碼已省略*/

public class DrinkActivity extends AppCompatActivity {

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????public void onFavoriteClicked(View view){

????????int drinkId=getIntent().getIntExtra(EXTRA_DRINKID,0);

????????new UpdateDrinkTask().execute(drinkId);

????}

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????private class UpdateDrinkTask extends AsyncTask<Integer,Void,Boolean>{

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????????private ContentValues drinkvalues;

????????@Override

????????protected void onPreExecute() {

???????? /*執行初始化任務，可以在此進行一些變量的值的初始化*/

????????????CheckBox favorite=(CheckBox)findViewById(R.id.favorite);

????????????drinkvalues=new ContentValues();

????????????drinkvalues.put("FAVORITE",favorite.isChecked());

????????}

????????@Override

????????protected Boolean doInBackground(Integer... integers) {

????????????/*執行費時任務，返回一個boolean值，可以在此執行一些數據庫等費時操作*/

????????????int drinkId=getIntent().getIntExtra(EXTRA_DRINKID,0);

????????????SQLiteOpenHelper helper=new StarbuzzDatabaseHelper(DrinkActivity.this);

????????????try{

????????????????SQLiteDatabase db=helper.getWritableDatabase();

????????????????db.update("DRINK",drinkvalues,"_id=?",new String[]{Integer.toString(drinkId)});

????????????????return true;

????????????}catch (SQLException e){

????????????????return false;

????????????}

????????}

????????@Override

????????protected void onPostExecute(Boolean aBoolean) {

???????????/*代碼*/

????????}

????}

}

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