Android数据持久化之Preferences机制详解

package com.example.data_sharedpreferences;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.content.SharedPreferences;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
public class MainActivity extends Activity {
  private TextView text;
  private Button button;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    // 写入数据
    writeData();
    text = (TextView) findViewById(R.id.text);
    button = (Button) findViewById(R.id.button0);
    button.setOnClickListener(new OnClickListener() {
      @Override
      public void onClick(View v) {
        // TODO Auto-generated method stub
        // 读取数据
        readData();
      }
    });
  }
  /**
   * 写入数据
   */
  public void writeData() {
    // 设置权限为私有MODE_PRIVATE
    SharedPreferences sp_p = this.getSharedPreferences("ct_sp_private",
        Context.MODE_PRIVATE);
    // 通过SharedPreferences对象的编辑器对象Editor来实现存入数据
    SharedPreferences.Editor editor = sp_p.edit();
    // 通过该编辑器函数设置键值
    editor.putString("username", "marry_private");
    // 提交数据，并将数据写入xml文件中
    editor.commit();
    // 设置为只读
    SharedPreferences sp_or = this.getSharedPreferences("ct_sp_private",
        Context.MODE_WORLD_READABLE);
    sp_or.edit().putString("username", "marry_only_read").commit();
    // 设置为只写
    SharedPreferences sp_ow = this.getSharedPreferences("ct_sp_private",
        Context.MODE_WORLD_WRITEABLE);
    sp_ow.edit().putString("username", "marry_only_write").commit();
    // 设置为可读可写
    SharedPreferences sp_x = this.getSharedPreferences("ct_sp_private",
        Context.MODE_WORLD_READABLE + Context.MODE_WORLD_WRITEABLE);
    sp_x.edit().putString("username", "marry_write_read").commit();
  }
  /**
   * 读取数据
   * 通过SharedPreferences对象的键key可以获取到对应key的键值value。对于不同类型的键值有不同的函数：getBoolean
   * ,getInt,getFloat,getLong.
   */
  public void readData() {
    // TODO Auto-generated method stub
    text.setText("private_username:"
        + this.getSharedPreferences("ct_cp_private", 0).getString(
            "username", "marry_private")
        + "\r\n"
        + "read_username:"
        + this.getSharedPreferences("ct_cp_private", 0).getString(
            "username", "marry_only_read")
        + "\r\n"
        + "write_username:"
        + this.getSharedPreferences("ct_cp_private", 0).getString(
            "username", "marry_only_write")
        + "\r\n"
        + "write_read_username:"
        + this.getSharedPreferences("ct_cp_private", 0).getString(
            "username", "marry_write_read") + "\r\n");
  }
  @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;
  }
}

package com.example.data_sharedpreferences2;
import com.example.data_sharedpreferences2.R;
import android.os.Bundle;
import android.app.Activity;
import android.content.Context;
import android.content.pm.PackageManager.NameNotFoundException;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;
/**
 * 该程序的功能是访问data_sharedpreferences应用 Sharedpreferences访问另一个应用的条件：
 * 1、被访问的应用权限为可读或者可写 2、必须要知道被访问应用的包名
 *
 * @author marry
 *
 */
public class MainActivity extends Activity {
  private TextView text;
  private Button button;
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    text = (TextView) findViewById(R.id.text);
    button = (Button) findViewById(R.id.button0);
    button.setOnClickListener(new OnClickListener() {
      @Override
      public void onClick(View v) {
        // 访问应用1,并读取应用1的数据
        try {
          // 获得要访问应用的context
          Context ortherContext = createPackageContext(
              "com.example.data_sharedpreferences", 0);
          // 通过ortherContext.getSharedPreferences打开应用1的文件
          text.setText("private_username:"
              + ortherContext.getSharedPreferences(
                  "ct_cp_private", 0).getString("username",
                  "marry_private")
              + "\r\n"
              + "read_username:"
              + ortherContext.getSharedPreferences(
                  "ct_cp_private", 0).getString("username",
                  "marry_only_read")
              + "\r\n"
              + "write_username:"
              + ortherContext.getSharedPreferences(
                  "ct_cp_private", 0).getString("username",
                  "marry_only_write")
              + "\r\n"
              + "write_read_username:"
              + ortherContext.getSharedPreferences(
                  "ct_cp_private", 0).getString("username",
                  "marry_write_read") + "\r\n");
        } catch (NameNotFoundException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
        }
      }
    });
  }
  @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;
  }
}