数据存储（1）--键值对

public static String getPreferredLocation(Context context) {
    SharedPreferences prefs = PreferenceManager.getDefaultSharedPreferences(context);
    return prefs.getString(context.getString(R.string.pref_location_key),
            context.getString(R.string.pref_location_default));
}

public class MainActivity extends AppCompatActivity {
    SharedPreferences preferences;
    SharedPreferences.Editor editor;
    public static final String PRE_TAG = "sy.com";
    public static final String KEY_TIME = "time";
    public static final String KEY_RANDOM = "random";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        preferences = getSharedPreferences(PRE_TAG, MODE_PRIVATE);
        editor = preferences.edit();
        Button read = (Button)findViewById(R.id.read);
        Button write = (Button)findViewById(R.id.write);
        read.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String time = preferences.getString(KEY_TIME, null);
                int random = preferences.getInt(KEY_RANDOM, 0);
                String result = time == null ? "暂时未写入数据" : "上次写入时间" + time + "\n上次生成随机数" + random;
                Toast.makeText(getApplicationContext(), result, Toast.LENGTH_SHORT).show();
            }
        });
        write.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日 hh:mm:ss");
                editor.putString(KEY_TIME, sdf.format(new Date()));
                editor.putInt(KEY_RANDOM,(int)(Math.random() * 100));
                editor.commit();
            }
        });
    }
}