Android入门之使用SharedPreference存取信息详解

package org.mk.android.demo;
 
import android.content.Context;
import android.content.SharedPreferences;
import android.widget.Toast;
 
import java.util.HashMap;
import java.util.Map;
 
public class SharedPreferenceHelper {
 
    private final static String SP_TAG="demosp";
    private Context mContext;
 
    public SharedPreferenceHelper() {
    }
 
    public SharedPreferenceHelper(Context mContext) {
        this.mContext = mContext;
    }
    //定义一个保存数据的方法
    public void save(String loginId, String password) {
        SharedPreferences sp = mContext.getSharedPreferences(SP_TAG, Context.MODE_PRIVATE);
        SharedPreferences.Editor editor = sp.edit();
        editor.putString("loginId", loginId);
        editor.putString("password", password);
        editor.commit();
        Toast.makeText(mContext, "信息已写入SharedPreference["+SP_TAG+"]中", Toast.LENGTH_SHORT).show();
    }
 
    //定义一个读取SP文件的方法
    public Map<String, String> read() {
        Map<String, String> data = new HashMap<String, String>();
        SharedPreferences sp = mContext.getSharedPreferences(SP_TAG, Context.MODE_PRIVATE);
        data.put("loginId", sp.getString("loginId", ""));
        data.put("password", sp.getString("password", ""));
        return data;
    }
}

package org.mk.android.demo;
 
import androidx.appcompat.app.AppCompatActivity;
 
import android.content.Context;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.Toast;
 
import java.util.Map;
 
public class HomePage extends AppCompatActivity {
    private SharedPreferenceHelper spHelper;
    private Context ctx;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_home_page);
        Button buttonBack=(Button)findViewById(R.id.buttonBack);
        buttonBack.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                finish();
            }
        });
    }
    @Override
    protected void onStart() {
        super.onStart();
        ctx = getApplicationContext();
        spHelper = new SharedPreferenceHelper(ctx);
        Map<String, String> data = spHelper.read();
        Toast.makeText(ctx, "从SharedPreference中读到信息LoginId->" + data.get("loginId") + " password->" + data.get("password"), Toast.LENGTH_SHORT).show();
    }
}

package org.mk.android.demo;
 
import androidx.activity.result.ActivityResultLauncher;
import androidx.activity.result.contract.ActivityResultContracts;
import androidx.appcompat.app.AppCompatActivity;
 
import android.content.Context;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.Toast;
 
import java.util.Map;
 
public class MainActivity extends AppCompatActivity {
    private EditText editLoginId;
    private EditText editPassword;
    private Button buttonLogin;
    private String strLoginId;
    private String strPassword;
    private SharedPreferenceHelper spHelper;
    private Context ctx;
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        ctx = getApplicationContext();
        spHelper = new SharedPreferenceHelper(ctx);
        bindView();
    }
 
    private void bindView(){
        editLoginId = (EditText)findViewById(R.id.editLoginid);
        editPassword = (EditText)findViewById(R.id.editPassword);
        buttonLogin = (Button)findViewById(R.id.buttonLogin);
        buttonLogin.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View view) {
                strLoginId=editLoginId.getText().toString();
                strPassword=editPassword.getText().toString();
                spHelper.save(strLoginId,strPassword);
                Intent homeIt = new Intent(MainActivity.this, HomePage.class);
                startActivity(homeIt);
            }
        });
    }
    @Override
    protected void onStart() {
        super.onStart();
        ctx = getApplicationContext();
        spHelper = new SharedPreferenceHelper(ctx);
        Map<String, String> data = spHelper.read();
        Toast.makeText(ctx, "从SharedPreference中读到信息LoginId->" + data.get("loginId") + " password->" + data.get("password"), Toast.LENGTH_SHORT).show();
    }
}