问题
I am developing a math app for kids. After the user customizes the question options, I want to start another activity. I want to send a QuestionOptions object to the activity so that it can generate questions according to the options. So I created a QuestionnOptions class and implement Parcelable as the other answers showed me. However, there is an enum in my class. So I don't know what to do and let Android Studio generate the stuff needed:
package com.smartkidslovemaths;
import android.os.Parcel;
import android.os.Parcelable;
public class QuestionOptions implements Parcelable{
protected QuestionOptions(Parcel in) {
digitCount = in.readInt ();
}
public static final Creator<QuestionOptions> CREATOR = new Creator<QuestionOptions> () {
@Override
public QuestionOptions createFromParcel(Parcel in) {
return new QuestionOptions (in);
}
@Override
public QuestionOptions[] newArray(int size) {
return new QuestionOptions[size];
}
};
public QuestionOptions (OperationType operationType, int digitCount, boolean timerEnabled) {
this.operationType = operationType;
this.digitCount = digitCount;
this.timerEnabled = timerEnabled;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
}
@Override
public int hashCode () {
int value;
switch (operationType) {
case ADDITION:
value = 0;
break;
case SUBTRACTION:
value = 4;
break;
case ADD_AND_SUB:
value = 8;
case MULTIPLICATION:
value = 12;
break;
default:
value = 0;
break;
}
value += digitCount;
if (timerEnabled)
value += 100;
return value;
}
@Override
public boolean equals(Object o) {
return o.hashCode() == this.hashCode();
}
public enum OperationType {
ADDITION,
SUBTRACTION,
ADD_AND_SUB,
MULTIPLICATION
}
public boolean isTimerEnabled() {
return timerEnabled;
}
public void setTimerEnabled(boolean timerEnabled) {
this.timerEnabled = timerEnabled;
}
public OperationType getOperationType() {
return operationType;
}
public void setOperationType(OperationType operationType) {
this.operationType = operationType;
}
public int getDigitCount() {
return digitCount;
}
public void setDigitCount(int digitCount) {
this.digitCount = digitCount;
}
private OperationType operationType;
private int digitCount;
private boolean timerEnabled;
}
Now I send the QuestionOptions to the other activity:
QuestionOptions options = new QuestionOptions (
operation, digitCount,
cbTimerEnabled.isChecked ());
Intent i = new Intent (MainActivity.this, QuestionsActivity.class);
i.putExtra ("com.smartkidslovemaths.option", options);
startActivity (i);
I don't know whether I called the putExtra method correctly, but I continued to write code to get the question options in the other activity:
Intent i = getIntent ();
options = i.getExtras ().getParcelable ("com.smartkidslovemaths.options");
System.out.println (options.getDigitCount ());
System.out.println (options.getOperationType ());
System.out.println (options.isTimerEnabled ());
I printed out the options just because I want to see whether it has the correct stuff. But when I run the code, a NullPointerException occurred. Now I really don't know why this is happening. I tried changing the second line to
options = i.getExtras ().getParcelable ("options");
but the result is still the same. I think I must be doing something wrong in the QuestionOptions class, possibly because I didn't write to parcel but there's an enum! There isn't a method called writeEnum()! So can you tell me what I did wrong and how to fix it? And if I did something else wrong please tell me as well.
EDIT:
Here is my logcat:
08-24 16:14:20.841 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 251 | 750 |qvp_rtp_handle_signals iRet : 0
08-24 16:14:20.841 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 238 | 750 |qvp_rtp_handle_signals qpDplMainLoop: Calling imsSignalHandler
08-24 16:14:20.841 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 155 | 750 |qpdpl:imsSignalHandler: GLobal data NULL or Event list size is 0
08-24 16:14:20.841 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 243 | 750 |qvp_rtp_handle_signals add read fd : 9
08-24 16:14:22.823 389-389/? E/Parcel﹕ Reading a NULL string not supported here.
08-24 16:14:22.823 389-389/? E/Parcel﹕ Reading a NULL string not supported here.
08-24 16:14:25.836 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 251 | 750 |qvp_rtp_handle_signals iRet : 0
08-24 16:14:25.836 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 238 | 750 |qvp_rtp_handle_signals qpDplMainLoop: Calling imsSignalHandler
08-24 16:14:25.836 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 155 | 750 |qpdpl:imsSignalHandler: GLobal data NULL or Event list size is 0
08-24 16:14:25.836 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 243 | 750 |qvp_rtp_handle_signals add read fd : 9
08-24 16:14:29.730 7104-7104/? E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.smartkidslovemaths/com.smartkidslovemaths.QuestionsActivity}: java.lang.NullPointerException
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2266)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2316)
at android.app.ActivityThread.access$600(ActivityThread.java:150)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1298)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:213)
at android.app.ActivityThread.main(ActivityThread.java:5225)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:741)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
at dalvik.system.NativeStart.main(Native Method)
Caused by: java.lang.NullPointerException
at com.smartkidslovemaths.QuestionsActivity.onCreate(QuestionsActivity.java:16)
at android.app.Activity.performCreate(Activity.java:5133)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2230)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2316)
at android.app.ActivityThread.access$600(ActivityThread.java:150)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1298)
at android.os.Handler.dispatchMessage(Handler.java:99)
at android.os.Looper.loop(Looper.java:213)
at android.app.ActivityThread.main(ActivityThread.java:5225)
at java.lang.reflect.Method.invokeNative(Native Method)
at java.lang.reflect.Method.invoke(Method.java:525)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:741)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:557)
at dalvik.system.NativeStart.main(Native Method)
08-24 16:14:30.842 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 251 | 750 |qvp_rtp_handle_signals iRet : 0
08-24 16:14:30.842 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 238 | 750 |qvp_rtp_handle_signals qpDplMainLoop: Calling imsSignalHandler
08-24 16:14:30.842 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 155 | 750 |qpdpl:imsSignalHandler: GLobal data NULL or Event list size is 0
08-24 16:14:30.842 530-750/? E/Diag_Lib﹕ [IMS_FATAL]| 243 | 750 |qvp_rtp_handle_signals add read fd : 9
The exception occurred when executing the line:
System.out.println (options.getDigitCount ());
回答1:
I've tried your code and it seems the problem is with the parcelable object. Please update the following and it will work:
The constructor that accepts a Parcel object.
protected QuestionOptions(Parcel in) {
this.operationType = OperationType.valueOf(in.readString());
this.digitCount = in.readInt();
this.timerEnabled = in.readByte() != 0;
}
and the writeToParcel method.
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.operationType.name());
dest.writeInt(this.digitCount);
dest.writeByte((byte) (this.timerEnabled ? 1 : 0));
}
You can get the object from the intent in the following way:
final QuestionOptions options = getIntent().getParcelableExtra("com.smartkidslovemaths.option");
来源：https://stackoverflow.com/questions/32177391/how-to-send-an-object-to-another-activity-with-special-stuff