关于android中DatePicker程序的查询

在android中，为什么我不能使用此程序更改当前日期，即单击按钮后没有出现对话框，此程序是否有任何错误，请详细解释。感谢您的时间和考虑。

这是错误的方法签名：

package date_program.day_program;

   import java.util.Calendar;
   import android.app.Activity;
   import android.app.DatePickerDialog;
   import android.app.Dialog;
   import android.os.Bundle;
   import android.view.View;
   import android.view.View.OnClickListener;
   import android.widget.Button;
   import android.widget.DatePicker;
   import android.widget.TextView;

   public class SampleActivity extends Activity {
    /** Called when the activity is first created. */

    private int year,month,day;
    private TextView tvdisplay;
        private Button btpress;
        static final int DATE_DIALOG_ID=999;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        tvdisplay=(TextView)findViewById(R.id.textview1);
        btpress=(Button)findViewById(R.id.button1);
    tpress.setOnClickListener(new View.OnClickListener() {

       public void onClick(View arg0) {
       // TODO Auto-generated method stub

           showDialog(DATE_DIALOG_ID);  

           }
});
        final Calendar c=Calendar.getInstance();
            year=c.get(Calendar.YEAR);
            month=c.get(Calendar.MONTH);
            day=c.get(Calendar.DAY_OF_MONTH);
            Updatedisplay();
}

    protected Dialog OnCreateDialog(int Id)  {
    switch(Id) {    
    case DATE_DIALOG_ID:
    return new DatePickerDialog(this,datepicking,year,month,day);   
    }

     return null;
  }

      private DatePickerDialog.OnDateSetListener datepicking =new 

      DatePickerDialog.OnDateSetListener(){

            public void onDateSet(DatePicker arg0, int arg1, int arg2, int arg3) {

        // TODO Auto-generated method stub
                    year=arg1;
                    month=arg2;
                    day=arg3;
                        Updatedisplay();}
 };

  private void Updatedisplay() {
tvdisplay.setText(new StringBuilder().append("Date-").
   append(month+1).append("/").append(day).append("/").append(year));   
 }
 } 

正确的重写方法是

protecteddialog onCreateDialog（int-id）

（注意开头的小写字母“o”…大小写很重要！）。您可以通过以下两个简单的规则来保护自己，防止将来出现此类错误：

按照约定，方法名称应始终以小写字母开头。这就是整个框架的运作方式

对从框架重写的所有方法使用

@Override

注释。在这种情况下，编译器会告诉您，

OnCreateDialog

是对

OnCreateDialog

package date_program.day_program;

   import java.util.Calendar;
   import android.app.Activity;
   import android.app.DatePickerDialog;
   import android.app.Dialog;
   import android.os.Bundle;
   import android.view.View;
   import android.view.View.OnClickListener;
   import android.widget.Button;
   import android.widget.DatePicker;
   import android.widget.TextView;

   public class SampleActivity extends Activity {
    /** Called when the activity is first created. */

    private int year,month,day;
    private TextView tvdisplay;
        private Button btpress;
        static final int DATE_DIALOG_ID=999;

    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);

        tvdisplay=(TextView)findViewById(R.id.textview1);
        btpress=(Button)findViewById(R.id.button1);
    tpress.setOnClickListener(new View.OnClickListener() {

       public void onClick(View arg0) {
       // TODO Auto-generated method stub

           showDialog(DATE_DIALOG_ID);  

           }
});
        final Calendar c=Calendar.getInstance();
            year=c.get(Calendar.YEAR);
            month=c.get(Calendar.MONTH);
            day=c.get(Calendar.DAY_OF_MONTH);
            Updatedisplay();
}

    protected Dialog OnCreateDialog(int Id)  {
    switch(Id) {    
    case DATE_DIALOG_ID:
    return new DatePickerDialog(this,datepicking,year,month,day);   
    }

     return null;
  }

      private DatePickerDialog.OnDateSetListener datepicking =new 

      DatePickerDialog.OnDateSetListener(){

            public void onDateSet(DatePicker arg0, int arg1, int arg2, int arg3) {

        // TODO Auto-generated method stub
                    year=arg1;
                    month=arg2;
                    day=arg3;
                        Updatedisplay();}
 };

  private void Updatedisplay() {
tvdisplay.setText(new StringBuilder().append("Date-").
   append(month+1).append("/").append(day).append("/").append(year));   
 }
 } 

protected Dialog OnCreateDialog(int Id)  {
switch(Id) {    
case DATE_DIALOG_ID:
return new DatePickerDialog(this,datepicking,year,month,day);   
}