我们正在开发一个Android应用程序。在其中一个页面中，我们有15个拨动开关。当用户切换开关（为ON）时，布尔值将存储在共享首选项中。当用户在登录后重新访问页面时，切换开关将按照之前的选择显示。现在我们想将可以切换到ON的开关数量限制为9.在这方面，您的帮助最为明显。
我在这里放样本代码
import android.widget.CompoundButton;
import android.widget.CompoundButton.OnCheckedChangeListener;
public class favorites extends ActionBarActivity implements CompoundButton.OnCheckedChangeListener {
int c = 0;
String accdet;
String SessionID;
String favacctno,DATOFBIRTH;
Boolean isInternetPresent = false;
ConnectionDetector cd;
private ProgressDialog progressDialog;
CountDownTimer countDownTimer;
Logout lg;
String LastLogin;
String uname3;
String Custid;
String acountno;
String acctdet;
Switch tg,tg1,tg2,tg3,tg4,tg5,tg6,tg7,tg8,tg9,tga,tgb,tgc,tgd,tge,tgch;
private TextView switchStatus;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);
setContentView(R.layout.favorites);
final SharedPreferences sp = PreferenceManager
.getDefaultSharedPreferences(this);
tg.setOnCheckedChangeListener(this);
tg1.setOnCheckedChangeListener(this);
tg2.setOnCheckedChangeListener(this);
tg3.setOnCheckedChangeListener(this);
tg4.setOnCheckedChangeListener(this);
tg5.setOnCheckedChangeListener(this);
tg6.setOnCheckedChangeListener(this);
tg7.setOnCheckedChangeListener(this);
tg8.setOnCheckedChangeListener(this);
tg9.setOnCheckedChangeListener(this);
tga.setOnCheckedChangeListener(this);
tgb.setOnCheckedChangeListener(this);
tgc.setOnCheckedChangeListener(this);
tgd.setOnCheckedChangeListener(this);
tge.setOnCheckedChangeListener(this);
tgch.setOnCheckedChangeListener(this);
countDownTimer= new CountDownTimer(5*60000, 1000) {
public void onTick(long millisUntilFinished) {
// TextView tv10 = (TextView)findViewById(R.id.textView10);
// tv10.setText("" + millisUntilFinished / 1000);
}
public void onFinish() {
SessionID="L";
Editor edit = sp.edit();
edit.putString("SessionID", SessionID);
edit.commit();
Intent intent = new Intent(getApplicationContext(),Auth.class);
intent.setFlags(Intent.FLAG_ACTIVITY_CLEAR_TOP);
// intent.putExtra("EXIT", true);
intent.putExtra("Exp", "Expired");
startActivity(intent);
countDownTimer.cancel();
//showAlertDialog(AcctDetails.this, "Error","Session Expired.Kindly login once again.", false);
// finish() ;// finish ActivityB
}
}.start();
try{
String uname = sp.getString("UserName", "User");
SessionID=sp.getString("SessionID","SessionID");
favacctno=sp.getString("favacctno", "favacctno");
DATOFBIRTH=sp.getString("DATOFBIRTH", "DATOFBIRTH");
LastLogin = sp.getString("LastLogin", "LastLogin");
String usname = "Welcome " + uname;
TextView DispUName = (TextView) findViewById(R.id.textView9);
DispUName.setText(usname);
final String uname3=uname +"||"+SessionID+"||"+"No"+"||"+favacctno+"||"+DATOFBIRTH+"||"+LastLogin;
Custid = getIntent().getStringExtra("Custid");
}
catch
{
Toast.makeText(getBaseContext(),"Exception Occured.Kindly try again.",Toast.LENGTH_SHORT).show();
System.out.println( e);
}
}
final SharedPreferences sp = PreferenceManager
.getDefaultSharedPreferences(this);
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
// TODO Auto-generated method stub
if (isChecked)
{
c++;
}else
{
c--;
}
if (c<=9)
{
if (buttonView.getId()==R.id.accdet_Switch1)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("chqbkreq", true);
editor.commit();
}
else if (buttonView.getId()==R.id.acctsumm_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("accsumm", true);
editor.commit();
}
else if (buttonView.getId()==R.id.accstmt_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("accstmt", true);
editor.commit();
}
else if (buttonView.getId()==R.id.CRL_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("CRL", true);
editor.commit();
}
else if (buttonView.getId()==R.id.CSE_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("CSE", true);
editor.commit();
}
else if (buttonView.getId()==R.id.inwchq_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("inwchq", true);
editor.commit();
}
else if (buttonView.getId()==R.id.Unclramt_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("unclramt", true);
editor.commit();
}
else if (buttonView.getId()==R.id.depdet_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("depdet", true);
editor.commit();
}
else if (buttonView.getId()==R.id.depsumm_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("depsumm", true);
editor.commit();
}
else if (buttonView.getId()==R.id.depstmt_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("depstmt", true);
editor.commit();
}
else if (buttonView.getId()==R.id.loandet_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("loandet", true);
editor.commit();
}
else if (buttonView.getId()==R.id.loansumm_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("loansumm", true);
editor.commit();
}
else if (buttonView.getId()==R.id.loanstmt_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("loanstmt", true);
editor.commit();
}
else if (buttonView.getId()==R.id.AM_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("AM", true);
editor.commit();
}
else if (buttonView.getId()==R.id.forex_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("forex", true);
editor.commit();
}
else if (buttonView.getId()==R.id.chqbreq_Switch)
{
SharedPreferences.Editor editor = sp.edit();
editor.putBoolean("chqbkreq", true);
editor.commit();
}
Toast.makeText(favorites.this, "Success", Toast.LENGTH_SHORT).show();
}else
{
c--;
buttonView.setChecked(false);
Toast.makeText(favorites.this, "Only 9 Options can be selected.", Toast.LENGTH_SHORT).show();
}
}
}
App崩溃
05-12 16:23:42.362: W/dalvikvm(706): threadid=1: thread exiting with uncaught exception (group=0x409961f8)
05-12 16:23:42.392: E/AndroidRuntime(706): FATAL EXCEPTION: main
05-12 16:23:42.392: E/AndroidRuntime(706): java.lang.RuntimeException: Unable to start activity ComponentInfo{kvbank.kvb_ebook/kvbank.kvb_epassbook.favorites}: java.lang.NullPointerException
05-12 16:23:42.392: E/AndroidRuntime(706): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1955)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1980)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.app.ActivityThread.access$600(ActivityThread.java:122)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1146)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.os.Handler.dispatchMessage(Handler.java:99)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.os.Looper.loop(Looper.java:137)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.app.ActivityThread.main(ActivityThread.java:4340)
05-12 16:23:42.392: E/AndroidRuntime(706): at java.lang.reflect.Method.invokeNative(Native Method)
05-12 16:23:42.392: E/AndroidRuntime(706): at java.lang.reflect.Method.invoke(Method.java:511)
05-12 16:23:42.392: E/AndroidRuntime(706): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
05-12 16:23:42.392: E/AndroidRuntime(706): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
05-12 16:23:42.392: E/AndroidRuntime(706): at dalvik.system.NativeStart.main(Native Method)
05-12 16:23:42.392: E/AndroidRuntime(706): Caused by: java.lang.NullPointerException
05-12 16:23:42.392: E/AndroidRuntime(706): at kvbank.kvb_epassbook.favorites.onCreate(favorites.java:111)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.app.Activity.performCreate(Activity.java:4465)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
05-12 16:23:42.392: E/AndroidRuntime(706): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1919)
and 11 more........................
答案 0 :(得分：2)
在您的活动中实施CompoundButton.OnCheckedChangeListener，并添加以下代码：
tg.setOnCheckedChangeListener(this);
tg1.setOnCheckedChangeListener(this);
...
tge.setOnCheckedChangeListener(this);
现在你的onCheckedChanged（）：
@Override
public void onCheckedChanged(CompoundButton buttonView, boolean isChecked) {
if (isChecked)
{
count++;
}else
{
count--;
}
if (count<=9)
{
if (buttonView.getId()==R.id.accdet_Switch1)
{
//Do respective operation
}
else if (buttonView.getId()==R.id.acctsumm_Switch)
{
//Do respective operation
}
...
Toast.makeText(MainActivity.this, "Success", Toast.LENGTH_SHORT).show();
}else
{
count--;
buttonView.setChecked(false);
Toast.makeText(MainActivity.this, "Only 9 Options can be selected.", Toast.LENGTH_SHORT).show();
}
}
count 是一个全局整数变量。