SharedPreferences存储+SD卡存储

SharedPreferences存储

特点

1、保存少量的数据，且这些数据的格式非常简单。 存储5种原始数据类型: boolean, float, int, long, String
2、比如应用程序的各种配置信息（如是否打开音效、是否使用震动效果、小游戏的玩家积分等），记住密码功能，音乐播放器播放模式。

写数据

//写数据
//参数一 xml文件的名字 参数二 模式 MODE_PRIVATE 指定该SharedPreferences数据只能被本应用程序读写
SharedPreferences preferences = getSharedPreferences("login", MODE_PRIVATE);
//获取编辑对象
SharedPreferences.Editor edit = preferences.edit();
//写入数据的内容
edit.putInt("age", 18);
edit.putString("name", "科比");
edit.putBoolean("isMan", true);
edit.putFloat("price", 17.1f);
edit.putLong("id", 1234567);
//提交数据
edit.commit();

在执行完上面这段代码后系统会在data文件夹下自动生成文件

文件的内容也会自动创建

读数据

步骤1：得到SharedPreferences对象 getSharedPreferences(“文件的名称”,“文件的类型”);

步骤2：读取数据 String msg = sp.getString(key,defValue);

//读数据
btnRead.setOnClickListener(new View.OnClickListener() {
    @Override
    public void onClick(View v) {
        SharedPreferences login = getSharedPreferences("login", MODE_PRIVATE);
        String username = login.getString("name", "科比");
        Toast.makeText(MainActivity.this, ""+username, Toast.LENGTH_SHORT).show();
    }
});

案例（记住用户登录信息）

效果展示：

xml布局代码：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".Main2Activity">

    <LinearLayout
        android:padding="8dp"
        android:layout_margin="5dp"
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <TextView
            android:text="用户名："
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <EditText
            android:id="@+id/et_username"
            android:background="@drawable/border"
            android:paddingLeft="5dp"
            android:hint="请输入用户名"
            android:layout_width="match_parent"
            android:layout_height="50dp" />
    </LinearLayout>
    <LinearLayout
        android:padding="8dp"
        android:layout_margin="5dp"
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <TextView
            android:text="密    码："
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />
        <EditText
            android:id="@+id/et_password"
            android:background="@drawable/border"
            android:paddingLeft="5dp"
            android:hint="请输入密码"
            android:layout_width="match_parent"
            android:layout_height="50dp" />
    </LinearLayout>

    <LinearLayout
        android:orientation="horizontal"
        android:layout_width="match_parent"
        android:layout_height="wrap_content">
        <CheckBox
            android:id="@+id/cb_rem"
            android:layout_marginLeft="70dp"
            android:text="记住用户"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

        <Button
            android:id="@+id/btn_login"
            android:layout_marginLeft="40dp"
            android:text="登录"
            android:layout_width="195dp"
            android:layout_height="wrap_content" />
    </LinearLayout>
    
</LinearLayout>

java代码：

public class Main2Activity extends AppCompatActivity {
    private EditText etUsername;
    private EditText etPassword;
    private CheckBox cbRem;
    private Button btnLogin;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main2);

        initViews();

        //用户第二次登录
        SharedPreferences welcome = getSharedPreferences("welcome", MODE_PRIVATE);
        //判断是否记住
        boolean isCk = welcome.getBoolean("isCk", false);
        if (isCk){
            String username = welcome.getString("username", "");
            String password = welcome.getString("password", "");
            etUsername.setText(username);
            etPassword.setText(password);
            cbRem.setChecked(true);
        }

        //登录点击事件
        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //判断多选框选中状态
                if (cbRem.isChecked()){
                    String username = etUsername.getText().toString();
                    String password = etPassword.getText().toString();

                    //存入sp
                    SharedPreferences welcome = getSharedPreferences("welcome", MODE_PRIVATE);
                    SharedPreferences.Editor edit = welcome.edit();
                    edit.putString("username",username);
                    edit.putString("password",password);
                    //中间值，复选框是否被选中
                    edit.putBoolean("isCk",true);
                    edit.commit();
                }
            }
        });

    }

    private void initViews() {
        etUsername = (EditText) findViewById(R.id.et_username);
        etPassword = (EditText) findViewById(R.id.et_password);
        cbRem = (CheckBox) findViewById(R.id.cb_rem);
        btnLogin = (Button) findViewById(R.id.btn_login);
    }
}

外部文件存储(SD卡)

重要代码

(1)Environment.getExternalStorageState(); 判断SD卡是否

(2)Environment.getExternalStorageDirectory(); 获取SD卡的根目录

(3)Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES); 获取SD卡公开目录pictures文件夹

读写权限

必须在清单文件中添加读写权限

<uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
<uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />

为了更好的用户体验，6.0及之后的版本需要动态添加读写权限

//运行时权限
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {   
    //添加权限
    String[] strings = new String[]{Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE};
    //参数一：添加的权限数组，参数二：请求码
    requestPermissions(strings, 100);
}

我们可以去查看用户是否授权

//用户是否授权
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
    super.onRequestPermissionsResult(requestCode, permissions, grantResults);
    if (requestCode == 100 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
        Toast.makeText(this, "确定", Toast.LENGTH_SHORT).show();
    } else {
        Toast.makeText(this, "取消", Toast.LENGTH_SHORT).show();
    }
}

接下来补全代码，测试效果
xml：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".Main3Activity">

    <Button
        android:id="@+id/btn_write"
        android:text="Write"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />
    <Button
        android:id="@+id/btn_read"
        android:text="Read"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

java:

public class Main3Activity extends AppCompatActivity {
    private Button btnWrite;
    private Button btnRead;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main3);

        btnRead = (Button) findViewById(R.id.btn_read);
        btnWrite = (Button) findViewById(R.id.btn_write);

        //运行时权限
        if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {
            String[] strings = new String[]{Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE};
            requestPermissions(strings, 100);
        }
        //读取SD卡数据
        btnRead.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            	//获取SD卡的根路径
                File file = Environment.getExternalStorageDirectory();
                FileInputStream fis = null;
                StringBuffer stringBuffer = new StringBuffer();
                try {
                    fis = new FileInputStream(new File(file,"a.txt"));
                    byte[] bytes = new byte[1024];
                    int len = 0;
                    while ((len = fis.read(bytes))!=-1){
                        stringBuffer.append(new String(bytes,0,len));
                    }
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                }
		//吐司从SD卡中读取到的信息
                Toast.makeText(Main3Activity.this, ""+stringBuffer, Toast.LENGTH_SHORT).show();
            }
        });


        //写入SD卡数据
        btnWrite.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                //获取SD卡的根路径
                File file = Environment.getExternalStorageDirectory();
                FileOutputStream fos = null;
                try {
                    fos = new FileOutputStream(new File(file, "a.txt"));
                    fos.write("这是信息".getBytes());
                } catch (FileNotFoundException e) {
                    e.printStackTrace();
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    if (fos != null) {
                        try {
                            fos.close();
                        } catch (IOException e) {
                            e.printStackTrace();
                        }
                    }
                }
            }
        });
    }

    //用户是否授权
    @Override
    public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
        super.onRequestPermissionsResult(requestCode, permissions, grantResults);
        if (requestCode == 100 && grantResults[0] == PackageManager.PERMISSION_GRANTED) {
            Toast.makeText(this, "确定", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "取消", Toast.LENGTH_SHORT).show();
        }

    }
}

案例（从网络下载图片保存到SD卡，再读取到页面）

xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context=".Main4Activity">

    <Button
        android:id="@+id/btn_load"
        android:text="下载图片"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/btn_set"
        android:text="设置图片"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <ImageView
        android:id="@+id/iv_pic"
        android:src="@mipmap/ic_launcher_round"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

</LinearLayout>

java:

public class Main4Activity extends AppCompatActivity {
    private Button btnLoad;
    private Button btnSet;
    private ImageView ivPic;
    private String picUrl = "http://www.qubaobei.com/ios/cf/uploadfile/132/9/8289.jpg";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main4);
        btnLoad = (Button) findViewById(R.id.btn_load);
        btnSet = (Button) findViewById(R.id.btn_set);
        ivPic = (ImageView) findViewById(R.id.iv_pic);


        //从网络上下载图片存储到SD卡中
        btnLoad.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            	//开启网络下载的异步任务
                new MyTask().execute(picUrl);
            }
        });

        //从文件中读取图片
        btnSet.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                File file = Environment.getExternalStorageDirectory();
                Bitmap bitmap = BitmapFactory.decodeFile(new File(file, "a.jpg").getAbsolutePath());
                ivPic.setImageBitmap(bitmap);
            }
        });
    }


    class MyTask extends AsyncTask<String, Void, String> {

        @Override
        protected String doInBackground(String... strings) {
            //写数据的流
            FileOutputStream fos = null;
            //读数据的流
            InputStream is = null;
            //向SD卡写的输入流
            HttpURLConnection connection = null;
            try {
                URL url = new URL(strings[0]);
                connection = (HttpURLConnection) url.openConnection();
                connection.connect();
                //判断响应码是否为200
                if (connection.getResponseCode() == 200) {
                    is = connection.getInputStream();
                    //判断SD卡是否挂载
                    if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                        //获取SD卡路径
                        File file = Environment.getExternalStorageDirectory();
                        fos = new FileOutputStream(new File(file, "a.jpg"));
                        byte[] bytes = new byte[1024];
                        int len = 0;
                        while ((len = is.read(bytes)) != -1) {
                            fos.write(bytes, 0, len);
                        }
                    }
                }

            } catch (MalformedURLException e) {
                e.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            }finally {
            //关闭流
                if (is!=null){
                    try {
                        is.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if (fos!=null){
                    try {
                        fos.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
                if (connection!=null){
                    connection.disconnect();
                }
            }
            return null;
        }
    }
}