重寫的BaseAdapter：
public class MyAdapter extends BaseAdapter {
List<UserInfo> userInfos=new ArrayList<UserInfo>();
Context context;
public MyAdapter(Context c,List<UserInfo> userInfos) {
// TODO Auto-generated constructor stub
this.context=c;
this.userInfos=userInfos;
}
public void setcotext(List<UserInfo> userInfos){
this.userInfos=userInfos;
}
@Override
public int getCount() {
// TODO Auto-generated method stub
return userInfos.size();
}
@Override
public Object getItem(int arg0) {
// TODO Auto-generated method stub
return userInfos.get(arg0);
}
@Override
public long getItemId(int arg0) {
// TODO Auto-generated method stub
return userInfos.get(arg0).getId();
}
@Override
public View getView(int arg0, View arg1, ViewGroup arg2) {
// TODO Auto-generated method stub
if(arg1==null){
arg1=LayoutInflater.from(context).inflate(R.layout.book_item, null);
}
TextView _context=(TextView) arg1.findViewById(R.id.content);
TextView _datetime=(TextView) arg1.findViewById(R.id.datetime);
UserInfo u=userInfos.get(arg0);
_context.setText(u.getContent());
_datetime.setText(u.getDatetime());
return arg1;
}
}
Activity的：
public class MainActivity extends Activity implements OnClickListener{
Button add;
Button re;
SQLiteDatabase db;
ListView listView;
MyAdapter adapter;
List<UserInfo> liUse;
protected void onRestart() {
// TODO Auto-generated method stub
super.onRestart();
shuaxin();
}
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
DbInit();
add=(Button) findViewById(R.id.add);
listView=(ListView) findViewById(R.id.lv);
registerForContextMenu(listView);
adapter=new MyAdapter(this , liUse);
listView.setAdapter(adapter);
}
public List<UserInfo> selectAll(){
List<UserInfo> ls=new ArrayList<UserInfo>();
Cursor cur=db.rawQuery(" select * from user ", null);
while (cur.moveToNext()) {
UserInfo u = new UserInfo();
u.setId(cur.getInt(cur.getColumnIndex("_id")));
u.setContent(cur.getString(cur.getColumnIndex("content")));
u.setDatetime(cur.getString(cur.getColumnIndex("datetime")));
ls.add(u);
}
return liUse;
}
@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;
}
@Override
public void onClick(View arg0) {
// TODO Auto-generated method stub
switch (arg0.getId()) {
case R.id.refresh:
shuaxin();
break;
case R.id.add:
Intent intent=new Intent(this,AddConActivity.class);
startActivity(intent);
break;
default:
break;
}
}
public void DbInit(){
DBHelper dbHelper=new DBHelper(this, "Cotext.db", null, 1);
db=dbHelper.getWritableDatabase();
}
class DBHelper extends SQLiteOpenHelper{
public DBHelper(Context context, String name, CursorFactory factory,
int version) {
super(context, name, factory, version);
// TODO Auto-generated constructor stub
}
@Override
public void onCreate(SQLiteDatabase arg0) {
// TODO Auto-generated method stub
SimpleDateFormat formatter = new SimpleDateFormat ("yyyy年MM月dd日 HH:mm:ss ");
Date curDate = new Date(System.currentTimeMillis());//獲取當前時間
String str = formatter.format(curDate);
arg0.execSQL("create table user ( _id integer primary key autoincrement , datetime text not null , content varchar(100))");
ContentValues cv=new ContentValues();
cv.put("datetime", str);
cv.put("content", "測試");
arg0.insert("user", "datetime", cv);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
// TODO Auto-generated method stub
}
}
private void shuaxin() {
liUse=selectAll();
adapter.setcotext(liUse);
adapter.notifyDataSetInvalidated();
}
}
get 和 set ：
public class UserInfo implements Serializable{
private int id;
private String datetime;
private String content;
public UserInfo() {
// TODO Auto-generated constructor stub
}
public UserInfo(int id,String datetime,String content) {
// TODO Auto-generated constructor stub
this.setId(id);
this.setContent(content);
this.setDatetime(datetime);
}
public UserInfo(String datetime,String content) {
// TODO Auto-generated constructor stub
this.setContent(content);
this.setDatetime(datetime);
}
public int getId() {
return id;
}
public void setId(int id) {
this.id = id;
}
public String getDatetime() {
return datetime;
}
public void setDatetime(String datetime) {
this.datetime = datetime;
}
public String getContent() {
return content;
}
public void setContent(String content) {
this.content = content;
}
}
異常
04-23 16:48:45.585: E/AndroidRuntime(1823): FATAL EXCEPTION: main
04-23 16:48:45.585: E/AndroidRuntime(1823): Process: com.example.notepad, PID: 1823
04-23 16:48:45.585: E/AndroidRuntime(1823): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.notepad/com.example.notepad.MainActivity}: java.lang.NullPointerException
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2219)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2269)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.app.ActivityThread.access$800(ActivityThread.java:135)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1196)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.os.Handler.dispatchMessage(Handler.java:102)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.os.Looper.loop(Looper.java:136)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.app.ActivityThread.main(ActivityThread.java:5045)
04-23 16:48:45.585: E/AndroidRuntime(1823): at java.lang.reflect.Method.invokeNative(Native Method)
04-23 16:48:45.585: E/AndroidRuntime(1823): at java.lang.reflect.Method.invoke(Method.java:515)
04-23 16:48:45.585: E/AndroidRuntime(1823): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:779)
04-23 16:48:45.585: E/AndroidRuntime(1823): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:595)
04-23 16:48:45.585: E/AndroidRuntime(1823): at dalvik.system.NativeStart.main(Native Method)
04-23 16:48:45.585: E/AndroidRuntime(1823): Caused by: java.lang.NullPointerException
04-23 16:48:45.585: E/AndroidRuntime(1823): at com.example.notepad.MyAdapter.getCount(MyAdapter.java:29)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.widget.ListView.setAdapter(ListView.java:480)
04-23 16:48:45.585: E/AndroidRuntime(1823): at com.example.notepad.MainActivity.onCreate(MainActivity.java:44)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.app.Activity.performCreate(Activity.java:5231)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1104)
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2163)
04-23 16:48:45.585: E/AndroidRuntime(1823): ... 11 more
04-23 16:48:45.585: E/AndroidRuntime(1823): at android.widget.ListView.setAdapter(ListView.java:480)
List liUse; liUse沒有初始化，是空指針吧，所以後面 adapter 中getCount 是崩潰了。
開始直接初始化就不會崩潰了，
List liUse = new ArrayList<>();
