체크박스 체크된 것을 앱 종료 후 다시 실행해도 그대로 유지하기 위해서
SharedPreferences를 이용해서 UI에 그대로 적용해주고 싶어서 아래와 같이 구현 했습니다.
그런데 check.setChecked(chk); 부분에서 java.lang.NullPointerException 에러가 납니다.
이게 겨우 안드로이드 입문에서 어려움이 많습니다.
고수님들의 조언 부탁 드립니다.
아래 소스와 에러로그 남깁니다.
그럼, 부탁 드리겠습다.
-------------------소스-----------------------------
package org.tacademy.listview;
import java.util.List;
import android.app.Activity;
import android.content.Context;
import android.content.BroadcastReceiver;
import android.content.Intent;
import android.content.IntentFilter;
import android.net.wifi.ScanResult;
import android.net.wifi.WifiInfo;
import android.net.wifi.WifiManager;
import android.os.Bundle;
import android.util.Log;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.CheckBox;
import android.widget.ListView;
import android.view.Menu;
import android.view.MenuItem;
import android.widget.TextView;
import android.content.SharedPreferences;
public class WifiListViewActivity extends Activity {
private String[] values = new String[50];
WifiManager mainWifi;
WifiReceiver receiverWifi;
ScreenReceiver receiverScreen;
List<ScanResult> wifiList;
StringBuilder sb = new StringBuilder();
WifiInfo wifiInfo; // hwjang
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
mainWifi = (WifiManager) getSystemService(Context.WIFI_SERVICE);
wifiInfo = mainWifi.getConnectionInfo(); // hwjang
//String name = wifiInfo.getSSID(); // hwjang
/* Wifi Broadcast*/
receiverWifi = new WifiReceiver();
registerReceiver(receiverWifi, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
if (!mainWifi.isWifiEnabled()) {
mainText.setText("isWifiEnabled failed\n");
return;
}
mainWifi.startScan();
mainText.setText("\nStarting Scan...\n");
/* Screen Broadcast*/
IntentFilter filter = new IntentFilter(Intent.ACTION_SCREEN_ON);
filter.addAction(Intent.ACTION_SCREEN_OFF);
BroadcastReceiver mReceiver = new ScreenReceiver();
registerReceiver(mReceiver, filter);
// 레이아웃 파일의 리스트뷰를 가져와 커스텀어답터를 세팅한다.
final ListView listView = (ListView) findViewById(R.id.listView);
AreaList al = new AreaList(this, 0);
listView.setAdapter(al);
}
public boolean onCreateOptionsMenu(Menu menu) {
menu.add(0, 0, 0, "Refresh");
return super.onCreateOptionsMenu(menu);
}
// 어플리케이션이 화면에서 사라질 때
@Override
protected void onStop() {
// TODO Auto-generated method stub
super.onStop();
/*
// UI 상태를 저장
SharedPreferences pref = getSharedPreferences("pref", Activity.MODE_PRIVATE);
SharedPreferences.Editor editor = pref.edit(); // Editor를 불러옴
CheckBox check = (CheckBox)findViewById(R.id.checkBox);
// 저장할 값들을 입력
editor.putBoolean("Check", check.isChecked());
// 저장
editor.commit();
*/
}
public boolean onMenuItemSelected(int featureId, MenuItem item) {
mainWifi.startScan();
mainText.setText("Starting Scan");
return super.onMenuItemSelected(featureId, item);
}
protected void onPause() {
unregisterReceiver(receiverWifi);
super.onPause();
}
protected void onResume() {
registerReceiver(receiverWifi, new IntentFilter(WifiManager.SCAN_RESULTS_AVAILABLE_ACTION));
super.onResume();
// Shared Preference를 불러옴
SharedPreferences pref = getSharedPreferences("pref", Activity.MODE_PRIVATE);
CheckBox check = (CheckBox)findViewById(R.id.checkBox);
// 저장된 값들을 불러옴
Boolean chk = pref.getBoolean("SlientMode", false);
System.out.println(chk);
if(pref != null)
check.setChecked(chk);
else
check.setChecked(true);
}
class WifiReceiver extends BroadcastReceiver {
public void onReceive(Context c, Intent intent) {
//sb = new StringBuilder();
wifiList = mainWifi.getScanResults();
System.out.println(values.length);
System.out.println(wifiList.size());
for(int i = 0; i < (wifiList.size()); i++) {
//sb.append(new Integer(i+1).toString() + ".");
values[i] = (wifiList.get(i)).SSID;
//sb.append("\n\n");
}
//mainText.setText(sb);
}
private void println(String string) {
// TODO Auto-generated method stub
}
}
class ScreenReceiver extends BroadcastReceiver {
public void onReceive(Context c, Intent intent) {
if (intent.getAction().equals(Intent.ACTION_SCREEN_OFF)) {
// turn Wi-Fi off
//mainWifi.setWifiEnabled(false);
} else if (intent.getAction().equals(Intent.ACTION_SCREEN_ON)) {
// turn Wi-Fi on
//mainWifi.setWifiEnabled(true);
}
}
}
private class AreaList extends ArrayAdapter<STRING> {
public AreaList(Context context, int textViewResourceId) {
super(context, textViewResourceId);
}
// 배열의 길이를 리턴하여 리스트의 개수를 계산한다.
@Override
public int getCount() {
return values.length;
}
// 배열의 개수만큼 리스트를 만든다.
@Override
public View getView(int position, View convertView, ViewGroup parent) {
if (convertView == null) {
LayoutInflater vi = (LayoutInflater) getSystemService(Context.LAYOUT_INFLATER_SERVICE);
convertView = vi.inflate(R.layout.list_items, null);
}
if (values[position] != null) {
TextView tv = (TextView) convertView.findViewById(R.id.textView);
if (tv != null) {
tv.setText(values[position]);
}
}
return convertView;
}
}
}
-------------------에러로그-----------------------------
01-23 18:43:15.917: D/AndroidRuntime(5547): Shutting down VM
01-23 18:43:15.917: W/dalvikvm(5547): threadid=1: thread exiting with uncaught exception (group=0x4001d7f0)
01-23 18:43:15.921: E/AndroidRuntime(5547): FATAL EXCEPTION: main
01-23 18:43:15.921: E/AndroidRuntime(5547): java.lang.RuntimeException: Unable to resume activity {org.tacademy.listview/org.tacademy.listview.WifiListViewActivity}: java.lang.NullPointerException
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3128)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3143)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2684)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.os.Handler.dispatchMessage(Handler.java:99)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.os.Looper.loop(Looper.java:123)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.ActivityThread.main(ActivityThread.java:4627)
01-23 18:43:15.921: E/AndroidRuntime(5547): at java.lang.reflect.Method.invokeNative(Native Method)
01-23 18:43:15.921: E/AndroidRuntime(5547): at java.lang.reflect.Method.invoke(Method.java:521)
01-23 18:43:15.921: E/AndroidRuntime(5547): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:858)
01-23 18:43:15.921: E/AndroidRuntime(5547): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
01-23 18:43:15.921: E/AndroidRuntime(5547): at dalvik.system.NativeStart.main(Native Method)
01-23 18:43:15.921: E/AndroidRuntime(5547): Caused by: java.lang.NullPointerException
01-23 18:43:15.921: E/AndroidRuntime(5547): at org.tacademy.listview.WifiListViewActivity.onResume(WifiListViewActivity.java:120)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1149)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.Activity.performResume(Activity.java:3823)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3118)
01-23 18:43:15.921: E/AndroidRuntime(5547): ... 12 more
에러분석은 쉽습니다. 먼저 에러가 난 지점에서 뜨는 로그는 함수의 콜스택 순서대로 쌓이는 점을 명시하시고요,
01-23 18:43:15.921: E/AndroidRuntime(5547): Caused by: java.lang.NullPointerException
01-23 18:43:15.921: E/AndroidRuntime(5547): at org.tacademy.listview.WifiListViewActivity.onResume(WifiListViewActivity.java:120)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1149)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.Activity.performResume(Activity.java:3823)
01-23 18:43:15.921: E/AndroidRuntime(5547): at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3118)
이 부분이 핵심인데 스택이니 맨 위부터 보시면 되겠습니다. org.tacademy.listview.WifiListViewActivity 라는 class 의 onResume 함수에서 난 에러군요. 120번째 줄이라.. 거길 보시면 되겠네요.
Null Pointer Exception 은 문자그대로 널값을 읽으려고 해서 생긴 에러입니다.
String str = NULL;
str.toString(); <- 요러면 str이 널값이라 안에 아무것도 없으므로 위에서 String이라고 선언해줬어도 컴파일러는 얘가 뭔지 모릅니다.
이 부분을 유의하셔서 찾으시면 되겠네요.
(사실 120번째 줄이 어딘지 몰라서 못찾아드리겠..)