我是Android开发新手。我试图创建一个应用程序，在该应用程序中检索来自sql server的数据并在列表视图中显示。 我用edittext和复选框创建了一个自定义列表视图。 问题是来自服务器的数据不在listview中。我试图解决很多次，但每次出现相同的问题，即ResultSet为空。 我的代码是.........
Model.java的代码
public class Model {
private String name;
private boolean selected;
private String score;
public Model(String name) {
this.name = name;
selected = false;
score="";
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public boolean isSelected() {
return selected;
}
public void setSelected(boolean selected) {
this.selected = selected;
}
public String getScore() {
return score;
}
public void setScore(String score) {
this.score = score;
}
}
适配器类的代码
public class MyAdapter extends ArrayAdapter<Model> {
private final List<Model> list;
private final Activity context;
public MyAdapter(Activity context, List<Model> list)
{
super(context, R.layout.row, list);
this.context = context;
this.list = list;
}
static class ViewHolder
{
protected TextView text;
protected CheckBox checkbox;
protected EditText scores;
}
@Override
public View getView(int position, View convertView, ViewGroup parent)
{
View view = null;
if (convertView == null)
{
LayoutInflater inflator = context.getLayoutInflater();
view = inflator.inflate(R.layout.row, null);
final ViewHolder viewHolder = new ViewHolder();
viewHolder.text = (TextView) view.findViewById(R.id.label);
viewHolder.scores=(EditText) view.findViewById(R.id.txtAddress);
viewHolder.scores.addTextChangedListener(new TextWatcher()
{
public void onTextChanged(CharSequence s, int start, int before, int count) {
Model element=(Model)viewHolder.scores.getTag();
element.setScore(s.toString());
}
public void beforeTextChanged(CharSequence s, int start, int count,int after)
{
}
public void afterTextChanged(Editable s)
{
}
});
viewHolder.checkbox = (CheckBox) view.findViewById(R.id.check);
viewHolder.checkbox.setOnCheckedChangeListener(new CompoundButton.OnCheckedChangeListener() {
public void onCheckedChanged(CompoundButton buttonView,boolean isChecked) {
Model element = (Model) viewHolder.checkbox.getTag();
element.setSelected(buttonView.isChecked());
}
});
viewHolder.checkbox.setTag(list.get(position));
viewHolder.scores.setTag(list.get(position));
view.setTag(viewHolder);
}
else
{
view = convertView;
((ViewHolder) view.getTag()).checkbox.setTag(list.get(position));
((ViewHolder) view.getTag()).scores.setTag(list.get(position));
}
ViewHolder holder = (ViewHolder) view.getTag();
holder.text.setText(list.get(position).getName());
holder.scores.setText(list.get(position).getScore());
holder.checkbox.setChecked(list.get(position).isSelected());
return view;
}
}
MainActivity.java
public class MainActivity extends Activity {
ListView listView;
Button btnSave;
Connection connect;
ArrayAdapter<Model> adapter;
List<Model> list = new ArrayList<Model>();
public void initilize(){
connect=CONN("sa","cbo@morc","KULDEEP","122.160.255.218:1433");
}
@SuppressLint("NewApi")
private Connection CONN(String user,String pass,String db,String server){
StrictMode.ThreadPolicy policy=new StrictMode.ThreadPolicy.Builder().permitAll().build();
StrictMode.setThreadPolicy(policy);
Connection conn=null;
String connUrl=null;
try{
Class.forName("net.sourceforge.jtds.jdbc.Driver");
connUrl="jdbc:jtds:sqlserver://" + server + ";" + "databaseName=" + db + ";user=" + user + ";password=" + pass + ";";
conn=DriverManager.getConnection(connUrl);
}catch(SQLException se){
Log.e("ERROR", se.getMessage());
}catch(ClassNotFoundException cl){
Log.e("ERROR", cl.getMessage());
}catch(Exception e){
Log.e("ERROR", e.getMessage());
}
return conn;
}
public void onCreate(Bundle icicle) {
super.onCreate(icicle);
setContentView(R.layout.main);
listView = (ListView) findViewById(R.id.my_list);
btnSave = (Button)findViewById(R.id.btnSave);
adapter = new MyAdapter(this,getModel());
listView.setAdapter(adapter);
if(list.isEmpty()){
Toast.makeText(getApplicationContext(), "kuldeep", Toast.LENGTH_LONG).show();
}
btnSave.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View v) {
for (int i = 0; i < list.size(); i++) {
Toast.makeText(getBaseContext(), "Name : "+list.get(i).getName() +" Selected: "+list.get(i).isSelected()+"address: "+list.get(i).getScore().toString(), Toast.LENGTH_SHORT).show();
}
}
});
}
private List<Model> getModel() {
ResultSet rs;
try{
Statement smt=connect.createStatement();
rs=smt.executeQuery("select * from friends1");
while(rs.next()){
//Toast.makeText(getApplicationContext(), "0000", Toast.LENGTH_LONG).show();
list.add(new Model(rs.getString("name")));
}
}catch(Exception e){
e.printStackTrace();
}
return list;
}
}
main.xml中
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="vertical" >
<ListView
android:id="@+id/my_list"
android:layout_width="fill_parent"
android:layout_height="250px" />
<Button
android:text="Save"
android:id="@+id/btnSave"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
</LinearLayout>
row.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:orientation="horizontal" >
<TextView
android:id="@+id/label"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="@+id/label"
android:textSize="30sp"/>
<CheckBox
android:id="@+id/check"
android:layout_width="wrap_content"
android:layout_height="wrap_content"/>
<EditText
android:text=""
android:id="@+id/txtAddress"
android:layout_width="150px"
android:layout_height="wrap_content"/>
</LinearLayout>
如果有人请建议我这个问题的正确解决方案是什么... 如何在rs中获得价值。
logcat按摩。
08-20 14:33:41.173: W/System.err(717): java.lang.NullPointerException
08-20 14:33:41.173: W/System.err(717): at com.kuldeep.mylistedittext.MainActivity.getModel(MainActivity.java:92)
08-20 14:33:41.173: W/System.err(717): at com.kuldeep.mylistedittext.MainActivity.onCreate(MainActivity.java:69)
08-20 14:33:41.173: W/System.err(717): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-20 14:33:41.183: W/System.err(717): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1611)
08-20 14:33:41.183: W/System.err(717): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1663)
08-20 14:33:41.183: W/System.err(717): at android.app.ActivityThread.access$1500(ActivityThread.java:117)
08-20 14：33：41.183：W / System.err（717）：在android.app.ActivityThread $ H.handleMessage（ActivityThread.java:931）
答案 0 :(得分：1)
视图持有者方法应如下面的代码： -
if (convertView == null) {
convertView = mInflater.inflate(R.layout.list_item_icon_text,
parent, false);
holder = new ViewHolder();
holder.text = (TextView) convertView.findViewById(R.id.text);
holder.icon = (ImageView) convertView.findViewById(R.id.icon);
convertView.setTag(holder);
}
else
{
holder = (ViewHolder) convertView.getTag();
}
更改获取视图的代码。
更多尝试以下链接： -
http://vsvydenko.blogspot.in/2011/06/android-use-viewholder.html