Android 开发（13）数据存储技术

一、shared preferences存储

1、SP存取数据

写数据

读数据

2、QQ自动登录实现

public class MainActivity extends AppCompatActivity {
    private EditText editText1, editText2;
    private Button button;
    private String username = "stan", password = "stan123";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        editText1 = (EditText) findViewById(R.id.et1);
        editText2 = (EditText) findViewById(R.id.et2);
        button = (Button) findViewById(R.id.btn);
        final SharedPreferences sp = getSharedPreferences("stan", MODE_PRIVATE);
        String user = sp.getString("user", null);
        String pass = sp.getString("pass", null);
        if (user != null && pass != null) {
            if (user.equals(username) && pass.equals(password)) {
                Intent intent = new Intent(MainActivity.this, DetailActivity.class);
                startActivity(intent);
            }
        } else {
            button.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    String username_in = editText1.getText().toString();
                    String password_in = editText2.getText().toString();
                    if (!(username_in == null) && !(password_in == null)) {
                        if (username_in.equals(username) && password_in.equals(password)) {
                            SharedPreferences.Editor editor = sp.edit();
                            editor.putString("user", username_in);
                            editor.putString("pass", password_in);
                            editor.commit();
                            Intent intent = new Intent(MainActivity.this, DetailActivity.class);
                            startActivity(intent);
                        } else {
                            Toast.makeText(MainActivity.this, "用户名或者密码错误", Toast.LENGTH_SHORT).show();
                        }
                    } else {
                        Toast.makeText(MainActivity.this, "用户名或者密码为空", Toast.LENGTH_SHORT).show();
                    }

                }
            });
        }
    }
}

sharedPreferences 最终将数据保存在一个 xml 文件中，这个文件所在的位置是 data>data>包名>shared_prefs

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二、文件存储

• 这里的外部存储和内部存储不是指内置存储和SD的卡的差异

1、内部存储

简易备忘录的实现

public class MainActivity extends AppCompatActivity {
    private ImageButton btn_cancel, btn_save;
    private EditText editText;
    private FileInputStream fis;
    private FileOutputStream fos;
    private byte[] buffer;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        btn_cancel = (ImageButton) findViewById(R.id.cancel);
        btn_save = (ImageButton) findViewById(R.id.save);
        editText = (EditText) findViewById(R.id.et);
        btn_save.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                try {
                    fos = openFileOutput("inner", MODE_PRIVATE);
                    String text = editText.getText().toString();
                    fos.write(text.getBytes());
                    fos.flush();
                    Toast.makeText(MainActivity.this, "文件已经保存", Toast.LENGTH_SHORT).show();
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    if (fos != null) {
                        try {
                            fos.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        });

        //open app to open file
        try {
            fis = openFileInput("inner");
            buffer = new byte[fis.available()];
            fis.read(buffer);
            editText.setText(new String(buffer));
        } catch (FileNotFoundException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            if (fis != null) {
                try {
                    fis.close();
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }
        }

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

2、外部存储

• 简单来说我们的手机连接电脑，在电脑上能够查看的部分就是外部存储
• 上面的备忘录实例将获取输入和输出流的部分改为直接新建一个相应的FOS或者FIS对象并指定相应的File文件就可以了

关键代码

• 记得要在 manifest 里面开启权限

final File file = new File(Environment.getExternalStorageDirectory(),"stan.txt");
fos = new FileOutputStream(file);
fis = new FileInputStream(file);

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三、数据库存储

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四、数据共享