Android SharedReference-空指针异常
我正在尝试使用以下代码将某些内容保存到SharedReferences:Android SharedReference-空指针异常,android,sharedpreferences,Android,Sharedpreferences,我正在尝试使用以下代码将某些内容保存到SharedReferences: public class SignupActivity extends Activity { String str; @Override protected void onCreate(Bundle savedInstanceState) { // TODO Auto-generated method stub super.onCreate(savedInstan
public class SignupActivity extends Activity {
String str;
@Override
protected void onCreate(Bundle savedInstanceState) {
// TODO Auto-generated method stub
super.onCreate(savedInstanceState);
setContentView(R.layout.signup);
str = PreferenceManager.getDefaultSharedPreferences(this).getString(
"signedUp", null);
SharedPreferences app_preferences = PreferenceManager
.getDefaultSharedPreferences(this);
String text = app_preferences.getString("signedUp", null);
if(str.equals("YES")){
startActivity(new Intent("com.mobi.job.scout.MyTabActivity"));
}
markAsSignedUp();
}
public void markAsSignedUp() {
SharedPreferences.Editor localEditor = PreferenceManager
.getDefaultSharedPreferences(getBaseContext()).edit();
localEditor.putString("signedUp", "YES");
localEditor.commit();
Log.d("Signed Up!", ":)");
}
}
我在互联网上阅读并遵循了一些教程,但我发现了下面的错误。
这是logcat:
10-23 01:47:27.061: E/AndroidRuntime(408): FATAL EXCEPTION: main
10-23 01:47:27.061: E/AndroidRuntime(408): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.mobi.job.scout/com.mobi.job.scout.SignupActivity}: java.lang.NullPointerException
10-23 01:47:27.061: E/AndroidRuntime(408): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663)
10-23 01:47:27.061: E/AndroidRuntime(408): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679)
10-23 01:47:27.061: E/AndroidRuntime(408): at android.app.ActivityThread.access$2300(ActivityThread.java:125)
10-23 01:47:27.061: E/AndroidRuntime(408): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033)
10-23 01:47:27.061: E/AndroidRuntime(408): at android.os.Handler.dispatchMessage(Handler.java:99)
10-23 01:47:27.061: E/AndroidRuntime(408): at android.os.Looper.loop(Looper.java:123)
10-23 01:47:27.061: E/AndroidRuntime(408): at android.app.ActivityThread.main(ActivityThread.java:4627)
10-23 01:47:27.061: E/AndroidRuntime(408): at java.lang.reflect.Method.invokeNative(Native Method)
10-23 01:47:27.061: E/AndroidRuntime(408): at java.lang.reflect.Method.invoke(Method.java:521)
10-23 01:47:27.061: E/AndroidRuntime(408): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
10-23 01:47:27.061: E/AndroidRuntime(408): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
10-23 01:47:27.061: E/AndroidRuntime(408): at dalvik.system.NativeStart.main(Native Method)
10-23 01:47:27.061: E/AndroidRuntime(408): Caused by: java.lang.NullPointerException
10-23 01:47:27.061: E/AndroidRuntime(408): at com.mobi.job.scout.SignupActivity.onCreate(SignupActivity.java:28)
10-23 01:47:27.061: E/AndroidRuntime(408): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
10-23 01:47:27.061: E/AndroidRuntime(408): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627)
10-23 01:47:27.061: E/AndroidRuntime(408): ... 11 more
请让我知道我正在使用的代码有什么问题,我总是以武力接近而告终。谢谢
str = PreferenceManager.getDefaultSharedPreferences(this).getString(
"signedUp", null);
变量str为null,因为“signedUp”的值以前没有设置过值。检查if语句中的null
if(str != null && str.equals("YES")){
If将不会继续通过str!=如果为空,则为空
变量str为null,因为“signedUp”的值以前没有设置过值。检查if语句中的null
if(str != null && str.equals("YES")){
If将不会继续通过str!=null
如果为真。您还可以将getString的默认返回值从null更改为空字符串“”良好点。理想情况下,您希望使用一个常量值作为首选项的默认值,即private static final String default_SIGNEDUP_value=“”,或者在我的示例中为null。任何一种方法都可以。您还可以将getString的默认返回值从null更改为空字符串“”好的点。理想情况下,您希望使用一个常量值作为首选项的默认值,即private static final String default_SIGNEDUP_value=“”,或者在我的示例中为null。两种方法都可以。