weixin_54412384
weixin_54412384
采纳率0%
2021-02-28 10:09

大佬们帮我看看我这个为啥conn为空而且运行后闪退(代码是复制的)

布局XML文件

<?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=".MainActivity"
    android:orientation="vertical">
    <Button
        android:id="@+id/bt_send"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="查询"/>

    <TextView
        android:id="@+id/tv_response"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:textStyle="bold"/>
    <Button
        android:id="@+id/bt_delete"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="删除"/>
    <EditText
        android:id="@+id/ed_insert"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入要插入的数据"
        android:maxLines="2"/>
    <Button
        android:id="@+id/bt_insert"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="插入"/>
    <EditText
        android:id="@+id/ed_update"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:hint="请输入要更新的数据"
        android:maxLines="2"/>
    <Button
        android:id="@+id/bt_update"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="更新数据"/>
</LinearLayout>

mainactivity.java

package com.example.xxx;

import androidx.appcompat.app.AppCompatActivity;

import android.annotation.SuppressLint;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.TextView;

import com.mysql.jdbc.PreparedStatement;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class MainActivity extends AppCompatActivity implements onClick {
    private Button button, button_delete, button_insert, button_update;
    private TextView textView;
    private static final int TEST_USER_SELECT = 1;
    int i = 0, d = 0, z = 0;
    private EditText editText,editText_update;
    @SuppressLint("HandlerLeak")
    private Handler handler = new Handler(){
        @Override
        public void handleMessage(Message msg){
            String user;
            switch (msg.what){
                case TEST_USER_SELECT:
                    Test test = (Test)msg.obj;
                    user = test.getUser();
                    System.out.println("******");
                    System.out.println("******");
                    System.out.println("user:"+user);
                    textView.setText(user);
                    break;
            }
        }
    };
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        button =(Button) findViewById(R.id.bt_send);
        textView =(TextView) findViewById(R.id.tv_response);
        button_delete =(Button) findViewById(R.id.bt_delete);
        button_insert =(Button) findViewById(R.id.bt_insert);
        button_update =(Button) findViewById(R.id.bt_update);
        editText_update =(EditText) findViewById(R.id.ed_update);

    }
    @Override
    protected void onStart(){
        super.onStart();
        button.setOnClickListener((View.OnClickListener) this);
        button_delete.setOnClickListener((View.OnClickListener) this);
        button_insert.setOnClickListener((View.OnClickListener) this);
        button_update.setOnClickListener((View.OnClickListener) this);
    }
    @Override
    public void onClick(View view){
        switch (view.getId()){
            case R.id.bt_send:
                if (i<=3){
                    i++;
                }else {
                    i=1;
                }
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        Connection conn = null;
                        conn =(Connection) DBOpenHelper.getConn();
                        String sql = "select 姓名 from 学生";
                        Statement st;
                        try {
                            st =(Statement) conn.createStatement();
                            ResultSet rs = st.executeQuery(sql);
                            while (rs.next()){
                                Test test = new Test();
                                test.setUser(rs.getString(1));
                                Message msg = new Message();
                                msg.what = TEST_USER_SELECT;
                                msg.obj = test;
                                handler.sendMessage(msg);
                            }
                            st.close();
                            conn.close();
                        }catch (SQLException e){
                            e.printStackTrace();
                        }
                    }
                }).start();
                break;
            case R.id.bt_delete:
                d++;
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        Connection conn = null;
                        int u = 0;
                        conn = (Connection)DBOpenHelper.getConn();
                        String sql = "";
                        PreparedStatement pst;
                        try{
                            pst =(PreparedStatement) conn.prepareStatement(sql);
                            u = pst.executeUpdate();
                            pst.close();
                            conn.close();
                        }catch (SQLException e){
                            e.printStackTrace();
                        }
                    }
                }).start();
                break;
            case R.id.bt_insert:
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        Connection conn = null;
                        int u = 0;
                        conn = (Connection)DBOpenHelper.getConn();
                        String sql = "";
                        PreparedStatement pst;
                        try {
                            pst = (PreparedStatement)conn.prepareStatement(sql);
                            pst.setString(1,editText.getText().toString());
                            u = pst.executeUpdate();
                            pst.close();
                            conn.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
                }).start();
                break;
            case R.id.bt_update:
                z++;
                new Thread(new Runnable() {
                    @Override
                    public void run() {
                        Connection conn = null;
                        int u = 0;
                        conn = (Connection)DBOpenHelper.getConn();
                        String sql = "";
                        PreparedStatement pst;
                        try {
                            pst = (PreparedStatement)conn.prepareStatement(sql);
                            u = pst.executeUpdate();
                            pst.close();
                            conn.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
                }).start();
                break;
            default:
        }
    }
}

TEST文件

package com.example.xxx;

public class Test {
    private int id;
    private String user;
    public int getId(){
        return id;
    }
    public void setId(int id){
        this.id = id;
    }
    public String getUser(){
        return user;
    }
    public void setUser(String user){
        this.user = user;
    }


}

DBOpenHelper

package com.example.xxx;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;

public class DBOpenHelper {
    private static String diver = "com.mysql.jdbc.Driver";
    private static String url = "jdbc:mysql://192.168.0.103:3306/wdnmd";
    private static String user = "root";
    private static String password = "Q87683232q";

    public static Connection getConn(){
        Connection conn = null;
        try {
            Class.forName(diver);
            conn =(Connection) DriverManager.getConnection(url,user,password);
        } catch (ClassNotFoundException e){
            e.printStackTrace();
        }catch (SQLException e) {
            e.printStackTrace();
        }
        return conn;
    }
}
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2条回答

  • MacaoPark Xia_燚 1月前

    首先  jdbc:mysql://192.168.0.103:3306/wdnmd 端口防火墙是否允许?还有一般不要app直接连mysql。

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  • weixin_36479969 让暖阳护你周全 1月前

    建议 conn =(Connection) DriverManager.getConnection(url,user,password); 
    打个断点跟进去看一下那里报错了

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