Sharedpreferences的微调器问题

Question

Sorry,this is my first time to put questions in this site

My Function: I set two Buttons to restore and save the information in the Spinner and EditText with the function Sharedpreferences.

I execute the program at the first time. The program will appear the error state,if I click the Button "restore" to restore the information in Spinner. But I haven't met the problem when I restore the information in EditText.

This is the code in Spinner

private Spinner.OnItemSelectedListener getfeet = new OnItemSelectedListener() {
    @Override
    public void onItemSelected(AdapterView<?> parent, View v, int position,
            long id) {
        // TODO Auto-generated method stub
        feet_out = parent.getSelectedItemPosition() + 2;
        select_f = feet.getSelectedItemPosition(); //save the position you choose
        Toast.makeText(MainActivity.this,
                "you chose " + parent.getSelectedItem().toString(),
                Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {
        // TODO Auto-generated method stub
    }
};
private Spinner.OnItemSelectedListener getinch = new OnItemSelectedListener() {

    @Override
    public void onItemSelected(AdapterView<?> parent, View v, int position,
            long id) {
        // TODO Auto-generated method stub
        inch_out = parent.getSelectedItemPosition();
        select_i = inch.getSelectedItemPosition(); //save the position you choose
        Toast.makeText(MainActivity.this,
                "you chose " + parent.getSelectedItem().toString(),
                Toast.LENGTH_SHORT).show();
    }

    @Override
    public void onNothingSelected(AdapterView<?> parent) {
        // TODO Auto-generated method stub

    }

};

This is the code which executes the function of save in Sharedpreferences

private void save_() {
    settings = getSharedPreferences("DATA", 0);
    settings.edit().putInt("DATA_FEET", select_f) //store the position in DATA_FEET and DATA_INCH
            .putInt("DATA_INCH", select_i)
            .putString("DATA_WEIGHT", weight.getText().toString()).commit();
    Toast.makeText(MainActivity.this, R.string.done, Toast.LENGTH_SHORT) //save done
            .show();
}

This is the code which executes the function of restore in Sharedpreferences

private void restore_() {
    feet.setSelection(settings.getInt("DATA_FEET", select_f)); //restore the position
    inch.setSelection(settings.getInt("DATA_INCH", select_i));
    weight.setText(settings.getString("DATA_WEIGHT", "EMPTY"));

}

My problem is that I can't use the function of restore at the program executing at the first time. Is there any solution to solve the problem?? Because it is normal in EditText,but it is abnormal in Spinner. Thanks :))

This is the state. :))

    10-23 23:14:11.677: D/TextLayoutCache(26370): Using debug level: 0 - Debug Enabled: 0
    10-23 23:14:11.747: D/libEGL(26370): loaded /system/lib/egl/libGLES_android.so
    10-23 23:14:11.797: D/libEGL(26370): loaded /system/lib/egl/libEGL_mali.so
    10-23 23:14:11.827: D/libEGL(26370): loaded /system/lib/egl/libGLESv1_CM_mali.so
    10-23 23:14:11.827: D/libEGL(26370): loaded /system/lib/egl/libGLESv2_mali.so
    10-23 23:14:11.887: D/OpenGLRenderer(26370): Enabling debug mode 0
    10-23 23:14:16.762: D/AndroidRuntime(26370): Shutting down VM
    10-23 23:14:16.762: W/dalvikvm(26370): threadid=1: thread exiting with uncaught exception (group=0x40aaa210)
    10-23 23:14:16.802: E/AndroidRuntime(26370): FATAL EXCEPTION: main
    10-23 23:14:16.802: E/AndroidRuntime(26370): java.lang.NullPointerException
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at com.example.bmi.MainActivity.restore_(MainActivity.java:44)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at com.example.bmi.MainActivity.access$1(MainActivity.java:43)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at com.example.bmi.MainActivity$2.onClick(MainActivity.java:99)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at android.view.View.performClick(View.java:3574)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at android.view.View$PerformClick.run(View.java:14293)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at android.os.Handler.handleCallback(Handler.java:605)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at android.os.Handler.dispatchMessage(Handler.java:92)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at android.os.Looper.loop(Looper.java:137)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at android.app.ActivityThread.main(ActivityThread.java:4448)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at java.lang.reflect.Method.invokeNative(Native Method)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at java.lang.reflect.Method.invoke(Method.java:511)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
    10-23 23:14:16.802: E/AndroidRuntime(26370):    at dalvik.system.NativeStart.main(Native Method)

This is the method to call the restore_()

private OnClickListener reback_1 = new OnClickListener() {
    public void onClick(View v) {
        restore_();
    }
};

After I replaced the select_f and select_i into 0 , it appeared the problem

10-24 00:01:30.957: D/TextLayoutCache(28836): Using debug level: 0 - Debug Enabled: 0
10-24 00:01:31.017: D/libEGL(28836): loaded /system/lib/egl/libGLES_android.so
10-24 00:01:31.037: D/libEGL(28836): loaded /system/lib/egl/libEGL_mali.so
10-24 00:01:31.057: D/libEGL(28836): loaded /system/lib/egl/libGLESv1_CM_mali.so
10-24 00:01:31.057: D/libEGL(28836): loaded /system/lib/egl/libGLESv2_mali.so
10-24 00:01:31.087: D/OpenGLRenderer(28836): Enabling debug mode 0
10-24 00:01:36.262: D/AndroidRuntime(28836): Shutting down VM
10-24 00:01:36.262: W/dalvikvm(28836): threadid=1: thread exiting with uncaught exception (group=0x40aaa210)
10-24 00:01:36.282: E/AndroidRuntime(28836): FATAL EXCEPTION: main
10-24 00:01:36.282: E/AndroidRuntime(28836): java.lang.NullPointerException
10-24 00:01:36.282: E/AndroidRuntime(28836):    at com.example.bmi.MainActivity.restore_(MainActivity.java:44)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at com.example.bmi.MainActivity.access$1(MainActivity.java:43)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at com.example.bmi.MainActivity$2.onClick(MainActivity.java:99)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at android.view.View.performClick(View.java:3574)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at android.view.View$PerformClick.run(View.java:14293)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at android.os.Handler.handleCallback(Handler.java:605)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at android.os.Handler.dispatchMessage(Handler.java:92)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at android.os.Looper.loop(Looper.java:137)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at android.app.ActivityThread.main(ActivityThread.java:4448)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at java.lang.reflect.Method.invokeNative(Native Method)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at java.lang.reflect.Method.invoke(Method.java:511)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
10-24 00:01:36.282: E/AndroidRuntime(28836):    at dalvik.system.NativeStart.main(Native Method)
10-24 00:01:37.803: I/Process(28836): Sending signal. PID: 28836 SIG: 9

Answer 1

You are using the SharedPrefs wrong.

feet.setSelection(settings.getInt("DATA_FEET", select_f)); 

when you try to fetch the integer-value from sharedPref, you get returned null! because i think that you misunderstand how it is done:

settings.getInt("myKey", defaultValue);

returns you the value for the key "myKey". if "myKey" has no value set, then it returns you the "defaultValue". In your case it returns the current value of "select_f". And as it looks, the value of select_f is null, when you run your application for the first time.

So you have to decide whether to initialize "select_f" before you retrieve the sharedPrefs or you enter another defaultValue here.