android 开发android 10 数据存储问题 安卓开发数据存储

Android有4种数据存取方式 

SharedPreferences
轻量级键-值方式存储,以XML文件方式保存。 

File
采用java.io.*库所提供有I/O接口,读写文件。 

SQLite数据库
轻量级嵌入式内置数据库。 

ContentProvider
封装各种数据源(文件、数据库、网络),共享给多个应用

－－－－这次主要用到的数据储存方法是SharedPreferences－－－－

应用场景

（1）自动登录:记住登录用户名(密码) 

（2）保存播放位置:用手机播放器播放音乐,希望重启播放 器时,播放器能从上次停止的那首曲目开始播放;

（3）其他应用......

以（1）为例实现数据储存

在android中，

SharedPreferences是用来存储简单数据的工具类,通过用键值对（支持的数据格式:boolean,float,int,long,String）

的方式把简单的数据存储在应用程序的私有目录：(data/data/<packagename>/shared_prefs/)下指定的xml 文件中。

SharedPreferences本身仅仅为一个接口,程序无法直接创建 SharedPreferences实例。

即无法用SharedPreferences sp = new SharedPreferences();这种方法获得实力。

只能通过Context提供的 getSharedPreferences(String name,int mode)方法来获取 SharedPreferences的实例。

其中name是要将数据储存到的文件的名字，mode指创建的文件的访问权限，支持三种：

1. 私有(MODE_PRIVATE):仅创建程序可读、写
2. 全局读(MODE_WORLD_READABLE):创建程序可读写,其他程序可读不可写
3. 全局写(MODE_WORLD_WRITEABLE):创建程序和其他程序都可写,但不可读!

(后两种模式可组合,用+号或|号.)

SharedPreferences接口主要方法：

＊String contains (String key) :检查是否已存在key这个关键字。

＊Map<String,?> getAll():返回preferences所有的数据(Map)。

＊Boolean getBoolean(String key, boolean defValue):获取Boolean型数据 

＊float getFloat(String key, float defValue):获取Float型数据

＊int getInt(String key, int defValue):获取Int型数据

＊long getLong(String key, long defValue):获取Long型数据

SharedPreferences接口本身并没有提供写入数据的能力,而是通过 SharedPreferences的内部接口Edit

SharedPreferences调用edit()即可获 得它所对应的Editor对象,该对象主要提供以下方法:

*Clear(),清空SharedPreferences里所有数据;

*putString(String key,*** Value),插入键值对；

*Remove(String key):删除SharedPreferences里指定的key对应的项; 

*commit():当Editor编辑完成后,调用该方法提交修改;

下面通过代码来说明：

package com.example.ex7;

import java.io.BufferedReader;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.ArrayList;
import java.util.Map;

import android.app.Activity;
import android.content.Intent;
import android.content.SharedPreferences;
import android.content.SharedPreferences.Editor;
import android.net.Uri;
import android.os.Bundle;
import android.util.Log;
import android.view.Menu;
import android.view.MenuItem;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;
import android.widget.Toast;

public class MainActivity extends Activity {
	private AutoCompleteTextView name;
	private EditText password;
	public static final String DATABASE = "Database";
	public static final String PATH = "/data/data/com.example.ex7/shared_prefs/Database.xml";
	public static final int FILE_SELECT_CODE = 1;
	private SharedPreferences sp;
	Editor editor;

	Button insert, delete, query, clear;
	Button showFile;
	TextView showResult;

	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		Log.i("oncreate", "heidi4");
		name = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView);
		password = (EditText) findViewById(R.id.editPassword);
		insert = (Button) findViewById(R.id.insertButton);
		delete = (Button) findViewById(R.id.deleteButton);
		query = (Button) findViewById(R.id.queryButton);
		clear = (Button) findViewById(R.id.clearButton);
		showFile = (Button) findViewById(R.id.button5);
		showResult = (TextView) findViewById(R.id.textView3);
		sp = getSharedPreferences(DATABASE, Activity.MODE_PRIVATE);
		editor = sp.edit();

		name.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				initAutoComplete(name);
			}
		});

		insert.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				String userName = name.getText().toString();
				String userPassword = password.getText().toString();
				editor.putString(userName, userPassword);
				editor.commit();
			}
		});

		delete.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				String userName = name.getText().toString();
				editor.remove(userName);
				editor.commit();
			}
		});

		query.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				String userName = name.getText().toString();
				String userPassword = sp.getString(userName, "none");
				showResult.setText("key = " + userName + " value = "
						+ userPassword);
			}
		});

		clear.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				editor.clear();
				editor.commit();
			}
		});

		showFile.setOnClickListener(new OnClickListener() {
			@Override
			public void onClick(View v) {
				showFileChooser();
			}
		});

	}

	private String getUserName() {
		Log.i("getUsername", "heidi10");
		Map<String, ?> map = sp.getAll();
		Log.i("getUsername", "heidi11");
		String content = new String();
		for (Map.Entry<String, ?> entry : map.entrySet()) {
			content += (entry.getKey() + " ");
		}
		return content;

	}

	private void initAutoComplete(AutoCompleteTextView auto) {
		String longhistory = getUserName();
		String[] autoStr = longhistory.split(" ");
		ArrayAdapter<String> autoadapter = new ArrayAdapter<String>(this,
				android.R.layout.simple_dropdown_item_1line, autoStr);

		auto.setAdapter(autoadapter);
		auto.setThreshold(1);

	}

	private void showFileChooser() {
		Intent intent = new Intent(Intent.ACTION_GET_CONTENT);
		intent.setType("*/*");
		intent.addCategory(Intent.CATEGORY_OPENABLE);

		try {
			startActivityForResult(
					Intent.createChooser(intent, "Select a File to Upload"),
					FILE_SELECT_CODE);
		} catch (android.content.ActivityNotFoundException ex) {
			Toast.makeText(this, "Please install a File Manager.",
					Toast.LENGTH_SHORT).show();
		}
	}

	@Override
	protected void onActivityResult(int requestCode, int resultCode, Intent data) {
		switch (requestCode) {
		case FILE_SELECT_CODE:
			if (resultCode == RESULT_OK) {
				// Get the Uri of the selected file
				Uri uri = data.getData();
				String filePath = FileUtils.getPath(this, uri);
				String fileContext = readfile(filePath);
				showResult.setText(fileContext);
			}
			break;
		}
		super.onActivityResult(requestCode, resultCode, data);
	}

	private String readfile(String filePath) {
		StringBuffer buff = new StringBuffer();
		try {
			FileInputStream fin = new FileInputStream(filePath);
			BufferedReader reader = new BufferedReader(new InputStreamReader(
					fin));
			try {
				String str = reader.readLine();
				while (str != null) {
					buff.append(str);
					str = reader.readLine();
				}
			} catch (IOException e) {
				;
			}

		} catch (FileNotFoundException e) {
			;
		}
		return buff.toString();
	}

	@Override
	public boolean onCreateOptionsMenu(Menu menu) {
		// Inflate the menu; this adds items to the action bar if it is present.
		getMenuInflater().inflate(R.menu.main, menu);
		return true;
	}

	@Override
	public boolean onOptionsItemSelected(MenuItem item) {
		// Handle action bar item clicks here. The action bar will
		// automatically handle clicks on the Home/Up button, so long
		// as you specify a parent activity in AndroidManifest.xml.
		int id = item.getItemId();
		if (id == R.id.action_settings) {
			return true;
		}
		return super.onOptionsItemSelected(item);
	}
}

＝＝看来我还是不喜欢写注释