从数据库中单击一个微调器数据然后它会显示一些文本。但是我无法实现这一点。使用数据库将微分数据成功添加到微调器中。 这是我的java类文件。我在onItemSelected监听器编码中有错误。请告诉我如何解决这个问题。 主要活动：
package com.samir.spinner;
import java.util.ArrayList;
import java.util.List;
import java.util.Set;
import android.app.Activity;
import android.content.Context;
import android.database.Cursor;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.view.View.OnClickListener;
import android.view.inputmethod.InputMethodManager;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
public abstract class MainActivity extends Activity implements OnClickListener,
OnItemSelectedListener {
private EditText edittext;
private Button btnAdd;
private Spinner spinner;
DatabaseHelper db;
List<String> list;
ArrayAdapter<String> adapter;
TextView tv;
Set<String> s;
protected Cursor c;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
db = new DatabaseHelper(MainActivity.this);
edittext = (EditText) findViewById(R.id.editText1);
btnAdd = (Button) findViewById(R.id.btnadd);
spinner = (Spinner) findViewById(R.id.spinner1);
btnAdd.setOnClickListener(this);
spinner.setOnItemSelectedListener(this);
}
@Override
public void onClick(View v) {
String name = edittext.getText().toString().trim();
if (TextUtils.isEmpty(name)) {
// showToast("Please Enter Your Name");
edittext.setError("Please Enter Your Name");
edittext.requestFocus();
} else {
db.insertData(name);
edittext.setText("");
// Hiding the keyboard
InputMethodManager inputmangager = (InputMethodManager) getSystemService(Context.INPUT_METHOD_SERVICE);
inputmangager.hideSoftInputFromWindow(edittext.getWindowToken(), 0);
loadSpinner();
}
}
private void loadSpinner() {
// here i used Set Because Set doesn't allow duplicates.
Set<String> set = db.getAllData();
List<String> list = new ArrayList<String>(set);
adapter = new ArrayAdapter<String>(MainActivity.this,
android.R.layout.simple_spinner_item, list);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
spinner.setAdapter(adapter);
spinner.setWillNotDraw(false);
spinner.setOnItemSelectedListener(new OnItemSelectedListener() {
@Override
public void onItemSelected(AdapterView<?> parent, View v,
int position, long id) {
Object item=parent.getItemAtPosition(position);
tv=(TextView) findViewById(R.id.txt);
tv.setText((CharSequence) item);
}
@Override
public void onNothingSelected(AdapterView<?> arg0) {
// TODO Auto-generated method stub
}
});
}
}
这是我的logcat输出： logcat的：
08-05 08:34:51.647: E/AndroidRuntime(1586): FATAL EXCEPTION: main
08-05 08:34:51.647: E/AndroidRuntime(1586): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.samir.spinner/com.samir.spinner.MainActivity}: java.lang.InstantiationException: can't instantiate class com.samir.spinner.MainActivity
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2106)
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2230)
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1234)
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.os.Handler.dispatchMessage(Handler.java:99)
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.os.Looper.loop(Looper.java:137)
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.app.ActivityThread.main(ActivityThread.java:5041)
08-05 08:34:51.647: E/AndroidRuntime(1586): at java.lang.reflect.Method.invokeNative(Native Method)
08-05 08:34:51.647: E/AndroidRuntime(1586): at java.lang.reflect.Method.invoke(Method.java:511)
08-05 08:34:51.647: E/AndroidRuntime(1586): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
08-05 08:34:51.647: E/AndroidRuntime(1586): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
08-05 08:34:51.647: E/AndroidRuntime(1586): at dalvik.system.NativeStart.main(Native Method)
08-05 08:34:51.647: E/AndroidRuntime(1586): Caused by: java.lang.InstantiationException: can't instantiate class com.samir.spinner.MainActivity
08-05 08:34:51.647: E/AndroidRuntime(1586): at java.lang.Class.newInstanceImpl(Native Method)
08-05 08:34:51.647: E/AndroidRuntime(1586): at java.lang.Class.newInstance(Class.java:1319)
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.app.Instrumentation.newActivity(Instrumentation.java:1054)
08-05 08:34:51.647: E/AndroidRuntime(1586): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2097)
08-05 08:34:51.647: E/AndroidRuntime(1586): ... 11 more
08-05 08:37:09.820: I/Process(1586): Sending signal. PID: 1586 SIG: 9
这是我的DatabaseHelper类。 DatabaseHelper.java：
package com.samir.spinner;
import java.util.HashSet;
import java.util.Set;
import android.content.ContentValues;
import android.content.Context;
import android.database.Cursor;
import android.database.sqlite.SQLiteDatabase;
import android.database.sqlite.SQLiteOpenHelper;
public class DatabaseHelper extends SQLiteOpenHelper {
private static final int DB_VERSION = 1;
private static final String DB_NAME = "mydb";
private static final String TABLE_NAME = "mytable";
private static final String _id = "_id";
private static final String name = "name";
public DatabaseHelper(Context context) {
super(context, DB_NAME, null, DB_VERSION);
}
@Override
public void onCreate(SQLiteDatabase db) {
String createTableQuery = "create table " + TABLE_NAME + "(" + _id
+ " INTEGER PRIMARY KEY," + name + " TEXT)";
db.execSQL(createTableQuery);
}
@Override
public void onUpgrade(SQLiteDatabase db, int oldVersion, int newVersion) {
db.execSQL("drop table if exists " + TABLE_NAME);
onCreate(db);
}
public void insertData(String label) {
SQLiteDatabase db = this.getWritableDatabase();
ContentValues values = new ContentValues();
values.put(name, label);
db.insert(TABLE_NAME, null, values);
db.close();
}
public Set<String> getAllData() {
Set<String> set = new HashSet<String>();
String selectQuery = "select * from " + TABLE_NAME;
SQLiteDatabase db = this.getReadableDatabase();
Cursor cursor = db.rawQuery(selectQuery, null);
if (cursor.moveToFirst()) {
do {
set.add(cursor.getString(1));
} while (cursor.moveToNext());
}
cursor.close();
db.close();
return set;
}
}
答案 0 :(得分：0)
您正在将微调器的onitemselected侦听器设置为“this”上下文。这根本不起作用，这是一个无效的论点。试试这个：
spinner.setOnItemSelectedListener(new AdapterView.OnItemSelectedListener() {
public void onItemSelected(AdapterView<?> parent, View view, int position, long id) {
Object item = parent.getItemAtPosition(position);
}
public void onNothingSelected(AdapterView<?> parent) {
}
});
编辑：根据以下评论，我认为您的错误可能在这里：
tv.setText((CharSequence) item);
尝试执行item.getText（）。toString（）。如果这不起作用，省略getText（）并执行toString（）。不过我不确定。
答案 1 :(得分：0)
更改
Object item=parent.getItemAtPosition(position);
来自
String item = (String) parent.getItemAtPosition(position);
然后简单地写
tv.setText(item); rather then
tv.setText((CharSequence) item);