37.Android数据存储再整理

这次主要是对SD卡外部存储和SharedPreferences存储的补充说明
还是以qq案例来说

首先外部存储

存储的位置为/storage/emulated/0目录下 具体为你定义的地方这里也有个小坑
还有就是不需要使用内部存储的openFileOutput方法和openFileInput方法

首先要在清单文件里申请SD卡写读文件的权限
两种方式静态和动态申请
自然在清单文件里配置静态申请简单了
    </application>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>

然后看工具类的编写

也就是对内部存储的更改

package com.example.store;

import android.content.Context;
import android.os.Environment;

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;

//工具类 实现QQ的账号密码存储和读取
public class SDTool_qqAcitivity {
    public static boolean saveUser(Context context, String user, String pwd) {
        String state = Environment.getExternalStorageState();
        if (state.equals(Environment.MEDIA_MOUNTED)) {
//            File path = Environment.getExternalStorageDirectory();
            File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
//            File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOCUMENTS);
            File file = new File(path, "haha.txt");
            FileOutputStream fos = null;
            try {
//                fos = context.openFileOutput("haha.txt", Context.MODE_PRIVATE);
                fos= new FileOutputStream(file);
                //将数据转换为字节码的形式写入haha.txt中
                fos.write((user + ":" + pwd).getBytes());
            } catch (Exception e) {
                e.printStackTrace();
                return false;
            } finally {
                if (fos != null) {
                    try {
                        fos.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                        return false;
                    }
                }
            }
            return true;
        } else {
            return false;
        }

    }

    public static Map<String, String> getUser(Context context) {
        String state = Environment.getExternalStorageState();
        if (state.equals(Environment.MEDIA_MOUNTED)) {
//            File path = Environment.getExternalStorageDirectory();
           File path = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);


            File file = new File(path, "haha.txt");
            String str = "";
            FileInputStream fis = null;
            try {
//                fis = context.openFileInput("haha.txt");
                fis=new FileInputStream(file);
                byte[] buffer = new byte[fis.available()];
                fis.read(buffer);
                str = new String(buffer);
                HashMap<String, String> map = new HashMap<String, String>();
                String[] split = str.split(":");
                map.put("user", split[0]);
                map.put("pwd", split[1]);
                return map;
            } catch (Exception e) {
                e.printStackTrace();
                return null;
            } finally {
                if (fis != null) {
                    try {
                        fis.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
        }
        return null;
    }


}

坑坑坑 如果你获取路径写的是如下的活 会实现不了保存密码也不会在文件里找到
// File path = Environment.getExternalStorageDirectory();
你必须给他一个确定的地方
例如：
Filepath=Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS);
这样文件就保存到DOWNLOADS目录下了

还有个重要的坑

就是我一直想实现不了密码保存
原因是
// Map<String, String> user =SDTool_qqAcitivity.getUser(this);
boolean b = SPTool_qqAcitivity.saveUser(QQ_Activity.this, user, pwd);
你要确定你调用的是哪个工具

然后就是SharedPreferences存储

它主要是一个轻量级的 存储介绍方法吗 都在33里面介绍了 就不赘婿了
然后就是文件存储在：

对的存储的格式为xml

然后咱们看工具类的编写

主要就是调用编辑器方法
package com.example.store;

import android.content.Context;
import android.content.SharedPreferences;

//工具类 实现QQ的账号密码存储和读取
public class SPTool_qqAcitivity {
    public static boolean saveUser(Context context, String user, String pwd) {
        SharedPreferences sharedPreferences = context.getSharedPreferences("haha", Context.MODE_PRIVATE);
        SharedPreferences.Editor edit = sharedPreferences.edit();
        edit.putString("user", user);
        edit.putString("pwd", pwd);
        edit.commit();
        return true;
    }

    public static String getUser(Context context, String key) {
        SharedPreferences sharedPreferences = context.getSharedPreferences("haha", Context.MODE_PRIVATE);
        String string = sharedPreferences.getString(key, "没找到");
        return string;
    }
}

注意注意要在主文件中修改你调用的工具同上一样：
略微修改
因为改成了String方法

//        Map<String, String> user =SDTool_qqAcitivity.getUser(this);
//        user = Tool_qqAcitivity.getUser(this);
//        if (user != null) {
//            et_account.setText(user.get("user"));
//            et_password.setText(user.get("pwd"));
//        }
        String user = SPTool_qqAcitivity.getUser(this, "user");
        String pwd = SPTool_qqAcitivity.getUser(this, "pwd");
        et_account.setText(user);
        et_password.setText(pwd);

再来个小补充把 就是我33并没有trycatch处理异常

这样是不对的 所以在这里小小补充下代码

package com.example.store;

import android.content.SharedPreferences;
import android.os.Bundle;
import android.os.Environment;
import android.text.TextUtils;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

import androidx.annotation.Nullable;
import androidx.appcompat.app.AppCompatActivity;

import java.io.IOException;
import java.util.Map;

public class QQ_Activity extends AppCompatActivity {
    //初始化
    private EditText et_account;
    private EditText et_password;
    private Button btn_login;

    @Override
    protected void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_qq);
        et_account = findViewById(R.id.et_account);
        et_password = findViewById(R.id.et_password);
        btn_login = findViewById(R.id.btn_login);
//        Map<String, String> user =SDTool_qqAcitivity.getUser(this);
//        user = Tool_qqAcitivity.getUser(this);
//        if (user != null) {
//            et_account.setText(user.get("user"));
//            et_password.setText(user.get("pwd"));
//        }
        String user = SPTool_qqAcitivity.getUser(this, "user");
        String pwd = SPTool_qqAcitivity.getUser(this, "pwd");
        et_account.setText(user);
        et_password.setText(pwd);


        btn_login.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                String user = et_account.getText().toString().trim();
                String pwd = et_password.getText().toString();
                //检查是否为空
                if (TextUtils.isEmpty(user)) {
                    Toast.makeText(QQ_Activity.this, "请输入账号", Toast.LENGTH_SHORT).show();
                }
                if (TextUtils.isEmpty(pwd)) {
                    Toast.makeText(QQ_Activity.this, "请输入密码", Toast.LENGTH_SHORT).show();
                }
                Toast.makeText(QQ_Activity.this, "登录成功", Toast.LENGTH_SHORT).show();
                //保存用户信息 调用工具
                boolean b = SPTool_qqAcitivity.saveUser(QQ_Activity.this, user, pwd);
                if (b) {
                    Toast.makeText(QQ_Activity.this, "保存成功", Toast.LENGTH_SHORT).show();
                } else {
                    Toast.makeText(QQ_Activity.this, "保存失败", Toast.LENGTH_SHORT).show();
                }

            }
        });
    }

}

欧克了 那个SQLite数据库存储33中已经很清楚的介绍
那三个存储方法算over了 剩下的就是内容提供者和网络存储了