Question

设置listview适配器时出错

现在让我先告诉你我的程序是什么，我想从数据库中获取数据，因为我已经完成了所有其他的事情，主要关于我的问题是我想从数据库中取出列表。但是一开始我试图用静态内容（android，.net ...）来做它但它给出了一些错误。

这是我的代码

package com.example.z;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.Timer;
import java.util.TimerTask;
import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.graphics.Color;
import android.util.Log;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
import android.widget.TextView;
import android.widget.Toast;
import net.sourceforge.jtds.jdbc.*;

public class MainActivity extends Activity {

Button b1,b2,b3,b4,b5;
Button item1,item2,item3;
Button andro,dotnet;
Boolean flag = true;
int i;
ListView list;

TextView t1,t2,t3,t4;

String url = null;
Connection xyz = null;
Connection conn = null;

String s1,s2,s3;

String[] menulist;
ArrayAdapter<String> adapter = null;

String DBName="Lalit";
String UserName="sa";
String Password="123";

Color c;

ResultSet resultSet;
Statement statement = null;
ResultSet rs = null;

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.tables);

    abc();
    Initialise();
}
void abc()
{
    try {
        Class.forName("net.sourceforge.jtds.jdbc.Driver").newInstance();
        url ="jdbc:jtds:sqlserver://192.168.1.15;instanceName=MSSQLSERVER;DatabaseName="+DBName+";integratedSecurity=true;user="+UserName+";password="+Password;

        Timer myTimer = new Timer();
        myTimer.schedule(new TimerTask() {          
            @Override
            public void run() {
                asdf();
            }
        }, 10000);

        Toast.makeText(getBaseContext(), "Connected to server", Toast.LENGTH_SHORT).show();
    } catch (InstantiationException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (IllegalAccessException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    } catch (ClassNotFoundException e1) {
        // TODO Auto-generated catch block
        e1.printStackTrace();
    }
}
void asdf()
{
  try {
    conn =DriverManager.getConnection(url);
} catch (SQLException e) {
    // TODO Auto-generated catch block
    e.printStackTrace();
}
  selectitem();
}

void selectitem()
{
    try {
        statement=conn.createStatement();
        resultSet = statement.executeQuery("SELECT * FROM lalit_db;");

        while(resultSet.next()){
                s1 = resultSet.getString(1);
                s2 = resultSet.getString(2);
                s3 = resultSet.getString(3);
            Log.w(s2, resultSet.getString(3));
            }
    } catch (SQLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
        Log.w("It is the error", "............");
    }
}

void Initialise()
{
    b1 = (Button)findViewById(R.id.button1);
    b2 = (Button)findViewById(R.id.button2);
    b3 = (Button)findViewById(R.id.button3);
    b4 = (Button)findViewById(R.id.button4);
    b5 = (Button)findViewById(R.id.button5);

    item1 = (Button)findViewById(R.id.item1);
    item2 = (Button)findViewById(R.id.item2);

    andro = (Button)findViewById(R.id.android);
    dotnet = (Button)findViewById(R.id.dotnet);

    t1 = (TextView)findViewById(R.id.menu1);
    t2 = (TextView)findViewById(R.id.menu2);
    t3 = (TextView)findViewById(R.id.menu3);
    t4 = (TextView)findViewById(R.id.menu4);

    list=(ListView)findViewById(R.id.listView1);

        b1.setOnClickListener(new OnClickListener() {
            @Override
            public void onClick(View v) {
                // TODO Auto-generated method stub
                b1.setBackgroundColor(c.TRANSPARENT);
                b1.setTextColor(c.RED);

                setContentView(R.layout.menu_category);
            }
        });

        String[] values = new String[]{"Adroid Developer",".Net Developer","Java Developer","BA"};

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, android.R.id.text1, values);

    // On this next line it gives the error....
         list.setAdapter(adapter); 
}

 @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;
   }

我有3个xml文件但是这个文件中有列表。

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/LinearLayout1"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/darker_gray"
android:orientation="vertical" >

<TextView
    android:id="@+id/textView5"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:marqueeRepeatLimit="5"
    android:paddingLeft="50dp"
    android:text="Select the Category"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:textSize="25sp"
    android:textStyle="italic" />

<Button
    android:id="@+id/android"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Android Developer" />

<Button
    android:id="@+id/dotnet"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text=".Net Developer" />

<Button
    android:id="@+id/java"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Java Developer" />

<Button
    android:id="@+id/ba"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="BA" />

<ListView
          android:id="@+id/listView1"
          android:layout_height="wrap_content"
          android:layout_width="match_parent">
     </ListView>

</LinearLayout>

这是tables.xml：

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:background="@android:color/darker_gray" >

<TextView
    android:id="@+id/textView1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="21dp"
    android:text="Select the Table"
    android:textAppearance="?android:attr/textAppearanceMedium"
    android:textSize="20sp"
    android:textStyle="bold|normal|italic" />

<Button
    android:id="@+id/button3"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/button4"
    android:layout_alignBottom="@+id/button4"
    android:layout_centerHorizontal="true"
    android:text="T:3" />

<Button
    android:id="@+id/button2"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/button3"
    android:layout_alignBottom="@+id/button3"
    android:layout_toRightOf="@+id/button1"
    android:text="T:2" />

<Button
    android:id="@+id/button5"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBottom="@+id/button4"
    android:layout_alignParentRight="true"
    android:text="T:5" />

<Button
    android:id="@+id/button1"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/button2"
    android:layout_alignBottom="@+id/button2"
    android:layout_alignParentLeft="true"
    android:text="T:1" />

<Button
    android:id="@+id/button4"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/textView1"
    android:layout_marginTop="28dp"
    android:layout_toLeftOf="@+id/button5"
    android:text="T:4" />

<Button
    android:id="@+id/button6"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentLeft="true"
    android:layout_below="@+id/button2"
    android:text="T:6" />

<Button
    android:id="@+id/button7"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/button6"
    android:layout_alignBottom="@+id/button6"
    android:layout_alignLeft="@+id/button2"
    android:text="T:7" />

<Button
    android:id="@+id/button8"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/button7"
    android:layout_alignBottom="@+id/button7"
    android:layout_alignLeft="@+id/button3"
    android:text="T:8" />

<Button
    android:id="@+id/button9"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/button8"
    android:layout_alignBottom="@+id/button8"
    android:layout_alignLeft="@+id/button4"
    android:text="T:9" />

<Button
    android:id="@+id/button10"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/button9"
    android:layout_alignBottom="@+id/button9"
    android:layout_alignParentRight="true"
    android:text="T:10" />

</RelativeLayout>

这是我的完整Logcat：

01-02 09:15:19.889: E/Trace(5651): error opening trace file: No such file or directory (2)
01-02 09:15:20.729: D/AndroidRuntime(5651): Shutting down VM
01-02 09:15:20.729: W/dalvikvm(5651): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
01-02 09:15:20.738: E/AndroidRuntime(5651): FATAL EXCEPTION: main
01-02 09:15:20.738: E/AndroidRuntime(5651): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.z/com.example.z.MainActivity}: java.lang.NullPointerException
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2180)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.os.Handler.dispatchMessage(Handler.java:99)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.os.Looper.loop(Looper.java:137)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.app.ActivityThread.main(ActivityThread.java:5041)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at java.lang.reflect.Method.invokeNative(Native Method)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at java.lang.reflect.Method.invoke(Method.java:511)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at dalvik.system.NativeStart.main(Native Method)
01-02 09:15:20.738: E/AndroidRuntime(5651): Caused by: java.lang.NullPointerException
01-02 09:15:20.738: E/AndroidRuntime(5651):     at com.example.z.MainActivity.Initialise(MainActivity.java:169)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at com.example.z.MainActivity.onCreate(MainActivity.java:64)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.app.Activity.performCreate(Activity.java:5104)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1080)
01-02 09:15:20.738: E/AndroidRuntime(5651):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2144)
01-02 09:15:20.738: E/AndroidRuntime(5651):     ... 11 more

Answer 1

这是因为您已全局声明

ArrayAdapter<String> adapter = null;

并再次为 ArrayAdapter 创建一个变量

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, android.R.id.text1, values);

因此该变量存在冲突。

因此，对于解决方案Make Global Variable

ArrayAdapter<String> adapter;

并按

初始化

adapter = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1, android.R.id.text1, values);

编辑：

原因是 NPE ，因为您已经Decalred并初始化该tables.xml文件中的 ListView 这个xml文件中没有它而不是它找到另一个xml文件。你有 空指针异常 。

更新：

 b1.setOnClickListener(new OnClickListener() {
        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            b1.setBackgroundColor(c.TRANSPARENT);
            b1.setTextColor(c.RED);

            LayoutInflater infalter = getLayoutInflater();
            View v = infalter.inflate(R.layout.menu_category,null);
            list = (ListView)v.findViewById(R.id.listView);

        }
    });

您可以这样开始新的活动：

   Intent n = new Intent(SourceActivity.this , Destination.class);
   startActivity(n);

谢谢！

Answer 2

你的名单是什么？您可以使用ListView创建布局并在活动中找到listView，以便您可以setAdapter 这是tutorial

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/LinearLayout_search"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

    <ListView
        android:id="@+id/listView"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent" >
    </ListView>

</LinearLayout>

活动

ListView listView = (ListView)findViewById(R.id.listView);
// do something with listview

Answer 3

这是一个基本的tuto：ListView in one class

初始化您的ListView：listView = (ListView) findViewById(R.id.list);
启动适配器
ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, android.R.id.text1, values);
调用Listview.setAdapter(adapter)方法

listView.setAdapter(adapter);
这就是全部：）

修改

你做错了。当您致电setContentView(R.layout.tables);时，您的活动会使该布局膨胀，您可以调用findViewById(ID)来获取给定布局中的视图。如果视图不在该布局中，则调用findViewById通常会导致NullPointerException。

否则，如果要使用其他布局的视图，请手动对其进行充气。

要解决您的问题，请移动ListView中的tables.xml。

Answer 4

使用此代码

import android.os.Bundle;
import android.app.Activity;
import android.view.*;
import android.widget.*;
import java.util.*;
public class MainActivity extends Activity {
    ListView myListView;
    EditText addList;
    ArrayList<String> todoItems;
    ArrayAdapter<String> aa;

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

    myListView = (ListView)findViewById(R.id.listView1);
    addList = (EditText)findViewById(R.id.editText1);
    todoItems = new ArrayList<String>();
    aa = new ArrayAdapter<String>(this,android.R.layout.simple_list_item_1,todoItems);
    myListView.setAdapter(aa);
    addList.setOnKeyListener(new View.OnKeyListener() {
        public boolean onKey(View v, int keyCode, KeyEvent event) {
        if (event.getAction() == KeyEvent.ACTION_DOWN)
        if ((keyCode == KeyEvent.KEYCODE_DPAD_CENTER) ||
        (keyCode == KeyEvent.KEYCODE_ENTER)) {
        todoItems.add(0, addList.getText().toString());
        aa.notifyDataSetChanged();
        addList.setText("");
        return true;
        }
        return false;
        }
        });
        }
    }
}

Xml代码

<?xml version="1.0" encoding="utf-8" ?> 
- <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:orientation="vertical">
- <EditText android:id="@+id/editText1" android:layout_width="match_parent" android:layout_height="wrap_content" android:ems="10">
  <requestFocus /> 
  </EditText>
  <ListView android:id="@+id/listView1" android:layout_width="match_parent" android:layout_height="wrap_content" /> 
  </LinearLayout>

在Android中，我们可以在一个活动中使用Listview吗？

4 个答案: