读取和写入JSON文件

Question

在Android中，我有2个活动。 Mainactivity从2个edittext（USERNAME-PASSWORD）中获取输入，并将其写入位于 asset文件夹中的 file.json ，输出活动具有2个textview，它将读取值（USERNAME） -PASSWORD），然后从 file.json 中将文本设置为TextView。这是我尝试的距离。

MainActivity.java

package com.example.io;

import android.content.Context;
import android.content.Intent;
import android.os.Bundle;

import com.google.android.material.floatingactionbutton.FloatingActionButton;
import com.google.android.material.snackbar.Snackbar;

import android.view.View;
import com.fasterxml.jackson.core.*;
import com.fasterxml.jackson.annotation.*;
import com.fasterxml.jackson.databind.*;

import com.google.android.material.navigation.NavigationView;

import androidx.core.view.GravityCompat;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import android.view.Menu;
import android.view.MenuItem;
import android.widget.Button;
import android.widget.EditText;

import org.json.JSONObject;

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.FileWriter;
import java.io.InputStreamReader;

public class MainActivity extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener
{

    private EditText et1,et2;
    private Button b;
    String e1,e2;
    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        et1 = (EditText) findViewById(R.id.et1);
        et2 = (EditText) findViewById(R.id.et2);
        b = (Button) findViewById(R.id.b);

        e1=et1.getText().toString().trim();
        e2=et2.getText().toString().trim();

        b.setOnClickListener(new View.OnClickListener()
        {
            BufferedReader reader = null;
            DataOutputStream dos = null;
            BufferedWriter writer = null;

            @Override
            public void onClick(View v)
            {

                //ObjectMapper mapper = new ObjectMapper();
                try
                {
                    JSONObject jsonObject = new JSONObject();
                    jsonObject.put("id",et1);
                    jsonObject.put("password",et2);

                    String FILENAME = "file.json";

                    String string = jsonObject.toString();

                    FileOutputStream fos = openFileOutput(FILENAME, Context.MODE_PRIVATE);
                    fos.write(string.getBytes());
                    fos.close();

                    Intent intent = new Intent(MainActivity.this,Output.class);
                    startActivity(intent);
                }
                catch (Exception e)
                {
                    e.printStackTrace();
                    System.out.println(e.getMessage());
                }
            }
        });
    }

    @Override
    public void onBackPressed()
    {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START))
        {
            drawer.closeDrawer(GravityCompat.START);
        }
        else
        {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item)
    {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings)
        {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item)
    {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_input)
        {
            // Handle the camera action
        }
        else if (id == R.id.nav_output)
        {
            Intent intent = new Intent(MainActivity.this,Output.class);
            startActivity(intent);
        }

        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

Output.java

package com.example.io;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;



import com.google.android.material.navigation.NavigationView;

import androidx.core.view.GravityCompat;
import androidx.drawerlayout.widget.DrawerLayout;
import androidx.appcompat.app.ActionBarDrawerToggle;
import androidx.appcompat.app.AppCompatActivity;
import androidx.appcompat.widget.Toolbar;

import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;

import org.json.JSONArray;
import org.json.JSONObject;

import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;

import org.json.simple.parser.JSONParser;

public class Output extends AppCompatActivity
        implements NavigationView.OnNavigationItemSelectedListener
{
    private TextView tv1;
    private TextView tv2;

    String id,password;

    @Override
    protected void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_output);
        Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
        setSupportActionBar(toolbar);



        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        ActionBarDrawerToggle toggle = new ActionBarDrawerToggle(
                this, drawer, toolbar, R.string.navigation_drawer_open, R.string.navigation_drawer_close);
        drawer.addDrawerListener(toggle);
        toggle.syncState();

        NavigationView navigationView = (NavigationView) findViewById(R.id.nav_view);
        navigationView.setNavigationItemSelectedListener(this);

        tv1 = findViewById(R.id.tv1);
        tv2 = findViewById(R.id.tv2);
        String json = null;

        try
        {
            /*JSONParser jsonParser = new JSONParser();
            JSONArray jsonArray = (JSONArray) jsonParser.parse(new FileReader("C:\\Users\\I\\Desktop\\IO\\app\\src\\main\\assets\\file.json"));
            JSONObject jsonObject = jsonArray.getJSONObject(0);
            Functions functions = new Functions();
            Bundle bundle = functions.MakeBundleFromJSON(jsonObject);*/

            /*InputStream is =  Output.this.getAssets().open("file.json");
            int size = is.available();
            byte[] buffer = new byte[size];
            is.read(buffer);
            is.close();
            json = new String(buffer, "UTF-8");*/
            InputStream is = getAssets().open("file.json");
            int size = is.available();
            byte[] buffer = new byte[size];
            is.read(buffer);
            is.close();
            json = new String(buffer, "UTF-8");

            System.out.println(json);

            JSONObject obj = new JSONObject(json);


            tv1.setText(obj.getString("id"));
            tv2.setText(obj.getString("password"));
        }
        catch (Exception e)
        {
            e.printStackTrace();
            System.out.println(e.getMessage());
        }
    }

    @Override
    public void onBackPressed()
    {
        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        if (drawer.isDrawerOpen(GravityCompat.START))
        {
            drawer.closeDrawer(GravityCompat.START);
        }
        else
        {
            super.onBackPressed();
        }
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu)
    {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.output, menu);
        return true;
    }

    @Override
    public boolean onOptionsItemSelected(MenuItem item)
    {
        // Handle action bar item clicks here. The action bar will
        // automatically handle clicks on the Home/Up button, so long
        // as you specify a parent activity in AndroidManifest.xml.
        int id = item.getItemId();

        //noinspection SimplifiableIfStatement
        if (id == R.id.action_settings)
        {
            return true;
        }

        return super.onOptionsItemSelected(item);
    }

    @SuppressWarnings("StatementWithEmptyBody")
    @Override
    public boolean onNavigationItemSelected(MenuItem item)
    {
        // Handle navigation view item clicks here.
        int id = item.getItemId();

        if (id == R.id.nav_input)
        {
            // Handle the camera action
            Intent intent = new Intent(Output.this,MainActivity.class);
            startActivity(intent);
        }
        else if (id == R.id.nav_output)
        {

        }


        DrawerLayout drawer = (DrawerLayout) findViewById(R.id.drawer_layout);
        drawer.closeDrawer(GravityCompat.START);
        return true;
    }
}

我的问题是我在“输出”活动中看不到任何输出。

这是log 如果您需要仔细查看，请参见here in git

Answer 1

您可以将数据存储在活动中的“共享首选项”中，并且在关闭应用程序后数据仍将保留。

您可以访问以下指向Android开发人员官方网站的链接 Shared Preference

希望有帮助。