Question

我是Android Developement的初学者，

我想在我的Android应用客户端应用程序和带有JDBC连接的MySql数据库之间建立连接

这是代码

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.Statement;

import android.os.Bundle;
import android.app.Activity;
import android.view.Menu;
import android.widget.TextView;

        public class MainActivity extends Activity {


    private static final String url = "jdbc:mysql://localhost/echallenge8_hrm_db";
    private static final String user = "root";
    private static final String pass = "";


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        testDB();
    }

    @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;
    }

    /** Called when the activity is first created. */

    public void testDB() {
        TextView tv = (TextView)this.findViewById(R.id.text_view);

        try {
            Class.forName("com.mysql.jdbc.Driver");
            Connection con = DriverManager.getConnection(url, user, pass);
            /* System.out.println("Database connection success"); */

            String result = "Database connection success\n";
            Statement st = con.createStatement();
            ResultSet rs = st.executeQuery("select * from collaborateur");
            ResultSetMetaData rsmd = rs.getMetaData();

            while(rs.next()) {
                result += rsmd.getColumnName(1) + ": " + rs.getString(1) + "\n";
                result += rsmd.getColumnName(2) + ": " + rs.getString(2) + "\n";
                result += rsmd.getColumnName(3) + ": " + rs.getString(3) + "\n";
            }
            tv.setText(result);
        }
        catch(Exception e) {
            e.printStackTrace();
            tv.setText(e.toString());
        }   

    }

    }

我在这行中有错误：

TextView tv = (TextView)this.findViewById(R.id.text_view);

这是我的Generated R.class

/* AUTO-GENERATED FILE.  DO NOT MODIFY.
 *
 * This class was automatically generated by the
 * aapt tool from the resource data it found.  It
 * should not be modified by hand.
 */


public final class R {
    public static final class attr {
    }
    public static final class dimen {
        /**  Default screen margins, per the Android Design guidelines. 

         Customize dimensions originally defined in res/values/dimens.xml (such as
         screen margins) for sw720dp devices (e.g. 10" tablets) in landscape here.

         */
        public static final int activity_horizontal_margin=0x7f040000;
        public static final int activity_vertical_margin=0x7f040001;
    }
    public static final class drawable {
        public static final int ic_launcher=0x7f020000;
    }
    public static final class id {
        public static final int action_settings=0x7f080000;
    }
    public static final class layout {
        public static final int activity_main=0x7f030000;
    }
    public static final class menu {
        public static final int main=0x7f070000;
    }
    public static final class string {
        public static final int action_settings=0x7f050001;
        public static final int app_name=0x7f050000;
        public static final int hello_world=0x7f050002;
    }
    public static final class style {
        /** 
        Base application theme, dependent on API level. This theme is replaced
        by AppBaseTheme from res/values-vXX/styles.xml on newer devices.


            Theme customizations available in newer API levels can go in
            res/values-vXX/styles.xml, while customizations related to
            backward-compatibility can go here.


        Base application theme for API 11+. This theme completely replaces
        AppBaseTheme from res/values/styles.xml on API 11+ devices.

 API 11 theme customizations can go here. 

        Base application theme for API 14+. This theme completely replaces
        AppBaseTheme from BOTH res/values/styles.xml and
        res/values-v11/styles.xml on API 14+ devices.

 API 14 theme customizations can go here. 
         */
        public static final int AppBaseTheme=0x7f060000;
        /**  Application theme. 
 All customizations that are NOT specific to a particular API-level can go here. 
         */
        public static final int AppTheme=0x7f060001;
    }
}

这里是我的AndroidManifest.XML

<manifest xmlns:android="http://schemas.android.com/apk/res/android"
    package="com.example.xxxxx"
    android:versionCode="1"
    android:versionName="1.0" >

    <uses-sdk
        android:minSdkVersion="8"
        android:targetSdkVersion="18" />

    <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >
        <activity
            android:name="xxxxx.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>
    </application>

</manifest>


<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context=".MainActivity" >

    <TextView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="@string/hello_world" />

</RelativeLayout>

谢谢

Answer 1

从您的R.java文件中，您没有名为＆＃34; text_view＆＃34; - 您的XML布局需要使用＆＃34; @ + id＆＃34;标记每个元素。这将在R.java文件中生成，以供您的代码参考。

Answer 2

你有

<TextView
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/hello_world" />

您需要拥有textview的ID

像

  <TextView
    android:id="@+id/text_view"   // id text_view was missing
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="@string/hello_world" />

字符串开头的at符号（@）表示XML解析器应解析并扩展ID字符串的其余部分，并将其标识为ID资源。加号（+）表示这是一个新的资源名称，必须创建并添加到我们的资源中（在R.java文件中）。

http://developer.android.com/guide/topics/ui/declaring-layout.html

Android First应用程序，text_view错误

2 个答案: