文件存储
Context类中提供了一个openFileOutput()方法，可以用于将数据存储到指定文件中。
第一个参数是文件名
第二个参数是文件的操作模式
文件默认会存储到/data/data/package name/files/目录下
MainActivity.java
package com.zhoujian.persistentdata;import android.content.Context;import android.os.Bundle;import android.support.v7.app.AppCompatActivity;import android.text.TextUtils;import android.widget.EditText;import android.widget.Toast;import java.io.BufferedReader;import java.io.BufferedWriter;import java.io.FileInputStream;import java.io.FileOutputStream;import java.io.IOException;import java.io.InputStreamReader;import java.io.OutputStreamWriter;
public class MainActivity extends AppCompatActivity{
private EditText edit;
@Override
protected void onCreate(Bundle savedInstanceState)
{ super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
edit = (EditText) findViewById(R.id.edit); String inputText = loadData(); if (!TextUtils.isEmpty(inputText))
{
edit.setText(inputText);
edit.setSelection(inputText.length());
Toast.makeText(this, "恢复数据成功", Toast.LENGTH_SHORT).show();
}
}
@Override
protected void onDestroy()
{ super.onDestroy(); String inputText = edit.getText().toString();
saveData(inputText);
}
public void saveData(String inputText)
{
FileOutputStream out = null;
BufferedWriter writer = null; try
{ //MODE_PRIVATE:默认模式，表示当指定同样文件名的时候，所写的内容将会覆盖原文件中的内容
//MODE_APPEND:表示如果文件存在，就往文件里追加内容，不存在就创建
out = openFileOutput("file", Context.MODE_PRIVATE);
writer = new BufferedWriter(new OutputStreamWriter(out));
writer.write(inputText);
} catch (IOException e)
{
e.printStackTrace();
} finally
{ try { if (writer != null) {
writer.close();
}
} catch (IOException e) {
e.printStackTrace();
}
}
}
public String loadData()
{
FileInputStream in = null;
BufferedReader reader = null;
StringBuilder sb = new StringBuilder(); try
{ in = openFileInput("file");
reader = new BufferedReader(new InputStreamReader(in)); String line = ""; while ((line = reader.readLine()) != null)
{
sb.append(line);
}
} catch (IOException e)
{
e.printStackTrace();
} finally
{ if (reader != null)
{ try
{
reader.close();
} catch (IOException e)
{
e.printStackTrace();
}
}
} return sb.toString();
}
}Demo下载：https://github.com/zeke123/PersistentData
SharedPreferences 存储
SharedPreferences是采用键值对的方式存储数据的
点击CheckBox，用SharedPreferences存储数据，记住用户名和密码
LoginActivity.java
package com.zhoujian.sharedPreferences;import android.content.Intent;import android.content.SharedPreferences;import android.os.Bundle;import android.preference.PreferenceManager;import android.view.View;import android.widget.Button;import android.widget.CheckBox;import android.widget.EditText;import android.widget.Toast;
public class LoginActivity extends BaseActivity{
private SharedPreferences pref;
private SharedPreferences.Editor editor;
private EditText mAccount;
private EditText mPassword;
private Button login;
private CheckBox mCheckBox;
@Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_login);
pref = PreferenceManager.getDefaultSharedPreferences(this);
mAccount = (EditText) findViewById(R.id.account);
mPassword = (EditText) findViewById(R.id.password);
mCheckBox = (CheckBox) findViewById(R.id.remember_pass);
login = (Button) findViewById(R.id.login);
boolean isRemember = pref.getBoolean("remember_password", false); if (isRemember) { // 将账号和密码都设置到文本框中
String account = pref.getString("account", ""); String password = pref.getString("password", "");
mAccount.setText(account);
mPassword.setText(password);
mCheckBox.setChecked(true);
}
login.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) { String account = mAccount.getText().toString(); String password = mPassword.getText().toString(); // 如果账号是123456且密码是123456，就认为登录成功
if (account.equals("123456") && password.equals("123456")) {
editor = pref.edit(); if (mCheckBox.isChecked()) { // 检查复选框是否被选中
editor.putBoolean("remember_password", true);
editor.putString("account", account);
editor.putString("password", password);
} else {
editor.clear();
}
editor.apply();
Intent intent = new Intent(LoginActivity.this, MainActivity.class);
startActivity(intent);
finish();
} else {
Toast.makeText(LoginActivity.this, "账号或者密码错误", Toast.LENGTH_SHORT).show();
}
}
});
}
}Demo下载：https://github.com/zeke123/SharedPreferences
SQLite数据库存储
创建数据库
在mac上查看数据库的工具：SQLPro for SQLite
数据库文件位于：/data/data/package name/databases/目录下
MyDatabaseHelper.java
package com.zhoujian.sqlitedemo;import android.content.Context;import android.database.sqlite.SQLiteDatabase;import android.database.sqlite.SQLiteOpenHelper;import android.widget.Toast;
public class MyDatabaseHelper extends SQLiteOpenHelper {
private Context mContext; //integer：表示整型
//text:表示文本型
//real:表示浮点型
//blob:表示二进制类型
public static final String CREATE_BOOK = "create table Book ("
+ "id integer primary key autoincrement, "
+ "author text, "
+ "price real, "
+ "pages integer, "
+ "name text)";
public static final String CREATE_CATEGORY = "create table Category ("
+ "id integer primary key autoincrement, "
+ "category_name text, "
+ "category_code integer)";
public MyDatabaseHelper(Context context, String name,
SQLiteDatabase.CursorFactory factory, int version) { super(context, name, factory, version);
mContext = context;
}
@Override
public void onCreate(SQLiteDatabase db) {
db.execSQL(CREATE_BOOK);
db.execSQL(CREATE_CATEGORY);
Toast.makeText(mContext, "创建数据库成功", Toast.LENGTH_SHORT).show();
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) { //当数据库升级的时候，如果表存在，会先删除表，然后重新创建
db.execSQL("drop table if exists Book");
db.execSQL("drop table if exists Category");
onCreate(db);
}
}增删改查
MainActivity.java
package com.zhoujian.sqlitedemo;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.util.Log;import android.view.View;import android.widget.Button;import android.widget.Toast;
public class MainActivity extends AppCompatActivity{
private MyDatabaseHelper dbHelper;
private SQLiteDatabase mDb;
private Button mCreateDatabase;
private Button mAddData;
private Button mQueryButton;
private Button mDeleteButton;
private Button mUpdateData;
@Override
protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
dbHelper = new MyDatabaseHelper(this, "Book.db", null, 1);
initViews();
clickEvents();
}
private void initViews()
{
mCreateDatabase = (Button) findViewById(R.id.create_database);
mAddData = (Button) findViewById(R.id.add_data);
mQueryButton = (Button) findViewById(R.id.query_data);
mDeleteButton = (Button) findViewById(R.id.delete_data);
mUpdateData = (Button) findViewById(R.id.update_data);
}
private void clickEvents()
{
mCreateDatabase.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) { //getReadableDatabase():如果磁盘已满，将以只读的方式打开数据库
//getWritableDatabase():如果磁盘已满，将出现异常
mDb = dbHelper.getWritableDatabase();
}
});
mAddData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) { if(mDb!=null){
ContentValues values = new ContentValues(); // 插入第一条数据
values.put("name", "Android开发艺术探索");
values.put("author", "任玉刚");
values.put("pages", 494);
values.put("price", 65.5);
mDb.insert("Book", null, values);
values.clear(); // 插入第二条数据
values.put("name", "第一行代码");
values.put("author", "郭霖");
values.put("pages", 510);
values.put("price", 75);
mDb.insert("Book", null, values);
values.clear(); // 插入第三条数据
values.put("name", "疯狂Android讲义");
values.put("author", "李刚");
values.put("pages", 580);
values.put("price", 85);
mDb.insert("Book", null, values);
Toast.makeText(MainActivity.this, "添加数据成功", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(MainActivity.this, "请先创建数据库", Toast.LENGTH_SHORT).show();
}
}
});
mUpdateData.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) { if(mDb!=null){ //把Android开发艺术探索这本书的价格改为70
ContentValues values = new ContentValues();
values.put("price", 70);
mDb.update("Book", values, "name = ?", new String[] { "Android开发艺术探索" });
Toast.makeText(MainActivity.this, "更新数据成功", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(MainActivity.this, "请先创建数据库", Toast.LENGTH_SHORT).show();
}
}
});
mDeleteButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) { if(mDb!=null){ //删除页数大于500的书籍
mDb.delete("Book", "pages > ?", new String[] { "500" });
Toast.makeText(MainActivity.this, "删除数据成功", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(MainActivity.this, "请先创建数据库", Toast.LENGTH_SHORT).show();
}
}
});
mQueryButton.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) { if(mDb!=null){ // 查询Book表中所有的数据
Cursor cursor = mDb.query("Book", null, null, null, null, null, null); if (cursor.moveToFirst()) { do { // 遍历Cursor对象，取出数据并打印
String name = cursor.getString(cursor.getColumnIndex("name")); String author = cursor.getString(cursor.getColumnIndex("author"));
int pages = cursor.getInt(cursor.getColumnIndex("pages"));
double price = cursor.getDouble(cursor.getColumnIndex("price"));
Log.d("MainActivity", "书籍的名字： " + name);
Log.d("MainActivity", "书籍的作者： " + author);
Log.d("MainActivity", "书籍的页数： " + pages);
Log.d("MainActivity", "书籍的价格：" + price);
} while (cursor.moveToNext());
}
cursor.close();
Toast.makeText(MainActivity.this, "查询数据成功", Toast.LENGTH_SHORT).show();
}else {
Toast.makeText(MainActivity.this, "请先创建数据库", Toast.LENGTH_SHORT).show();
}
}
});
}
}
随时随地看视频
