SharedPreferences存儲+SD卡存儲

SharedPreferences存儲

外部文件存儲(SD卡)

SharedPreferences存儲

特點

1、保存少量的數據，且這些數據的格式非常簡單。 存儲5種原始數據類型: boolean, float, int, long, String
2、比如應用程序的各種配置信息（如是否打開音效、是否使用震動效果、小遊戲的玩家積分等），記住密碼功能，音樂播放器播放模式。

寫數據

//寫數據
//參數一 xml文件的名字 參數二 模式 MODE_PRIVATE 指定該SharedPreferences數據只能被本應用程序讀寫
SharedPreferences preferences = getSharedPreferences("login", MODE_PRIVATE);
//獲取編輯對象
SharedPreferences.Editor edit = preferences.edit();
//寫入數據的內容
edit.putInt("age", 18);
edit.putString("name", "科比");
edit.putBoolean("isMan", true);
edit.putFloat("price", 17.1f);
edit.putLong("id", 1234567);
//提交數據
edit.commit();

在執行完上面這段代碼後系統會在data文件夾下自動生成文件

文件的內容也會自動創建

讀數據

步驟1：得到SharedPreferences對象 getSharedPreferences(“文件的名稱”,“文件的類型”);

步驟2：讀取數據 String msg = sp.getString(key,defValue);

//讀數據
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（記住用戶登錄信息）

效果展示：

xml佈局代碼：

<?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="用戶名："
            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="請輸入用戶名"
            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    碼："
            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="請輸入密碼"
            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="記住用戶"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content" />

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

java代碼：

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();

        //用戶第二次登錄
        SharedPreferences welcome = getSharedPreferences("welcome", MODE_PRIVATE);
        //判斷是否記住
        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);
        }

        //登錄點擊事件
        btnLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {

                //判斷多選框選中狀態
                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);
                    //中間值，複選框是否被選中
                    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);
    }
}

外部文件存儲(SD卡)

重要代碼

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

(2)Environment.getExternalStorageDirectory(); 獲取SD卡的根目錄

(3)Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_PICTURES); 獲取SD卡公開目錄pictures文件夾

讀寫權限

必須在清單文件中添加讀寫權限

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

爲了更好的用戶體驗，6.0及之後的版本需要動態添加讀寫權限

//運行時權限
if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.M) {   
    //添加權限
    String[] strings = new String[]{Manifest.permission.READ_EXTERNAL_STORAGE, Manifest.permission.WRITE_EXTERNAL_STORAGE};
    //參數一：添加的權限數組，參數二：請求碼
    requestPermissions(strings, 100);
}

我們可以去查看用戶是否授權

//用戶是否授權
@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, "確定", Toast.LENGTH_SHORT).show();
    } else {
        Toast.makeText(this, "取消", Toast.LENGTH_SHORT).show();
    }
}

接下來補全代碼，測試效果
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);

        //運行時權限
        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);
        }
        //讀取SD卡數據
        btnRead.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            	//獲取SD卡的根路徑
                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();
                }
		//吐司從SD卡中讀取到的信息
                Toast.makeText(Main3Activity.this, ""+stringBuffer, Toast.LENGTH_SHORT).show();
            }
        });


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

    //用戶是否授權
    @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, "確定", Toast.LENGTH_SHORT).show();
        } else {
            Toast.makeText(this, "取消", Toast.LENGTH_SHORT).show();
        }

    }
}

案例（從網絡下載圖片保存到SD卡，再讀取到頁面）

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="下載圖片"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content" />

    <Button
        android:id="@+id/btn_set"
        android:text="設置圖片"
        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);


        //從網絡上下載圖片存儲到SD卡中
        btnLoad.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
            	//開啓網絡下載的異步任務
                new MyTask().execute(picUrl);
            }
        });

        //從文件中讀取圖片
        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) {
            //寫數據的流
            FileOutputStream fos = null;
            //讀數據的流
            InputStream is = null;
            //向SD卡寫的輸入流
            HttpURLConnection connection = null;
            try {
                URL url = new URL(strings[0]);
                connection = (HttpURLConnection) url.openConnection();
                connection.connect();
                //判斷響應碼是否爲200
                if (connection.getResponseCode() == 200) {
                    is = connection.getInputStream();
                    //判斷SD卡是否掛載
                    if (Environment.getExternalStorageState().equals(Environment.MEDIA_MOUNTED)) {
                        //獲取SD卡路徑
                        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 {
            //關閉流
                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;
        }
    }
}

SharedPreferences存儲+SD卡存儲

SharedPreferences存儲+SD卡存儲

SharedPreferences存儲

特點

寫數據

讀數據

案例（記住用戶登錄信息）

外部文件存儲(SD卡)

重要代碼

讀寫權限

案例（從網絡下載圖片保存到SD卡，再讀取到頁面）

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