Java 如何将一个对象发送到另一个具有特殊内容的活动?
我正在为孩子们开发一个数学应用程序。用户自定义问题选项后,我想开始另一个活动。我想向活动发送一个Java 如何将一个对象发送到另一个具有特殊内容的活动?,java,android,android-activity,parcelable,Java,Android,Android Activity,Parcelable,我正在为孩子们开发一个数学应用程序。用户自定义问题选项后,我想开始另一个活动。我想向活动发送一个QuestionOptions对象,以便它可以根据选项生成问题。因此,我创建了一个questionOptions类,并按照其他答案所示实现了Parcelable。但是,我的类中有一个枚举。所以我不知道该怎么做,让Android Studio生成所需的内容: package com.smartkidslovemaths; import android.os.Parcel; import android
QuestionOptions
对象,以便它可以根据选项生成问题。因此,我创建了一个questionOptions
类,并按照其他答案所示实现了Parcelable
。但是,我的类中有一个枚举。所以我不知道该怎么做,让Android Studio生成所需的内容:
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;
}
我不知道是否正确调用了putExtra
方法,但我继续编写代码以获取其他活动中的问题选项:
QuestionOptions options = new QuestionOptions (
operation, digitCount,
cbTimerEnabled.isChecked ());
Intent i = new Intent (MainActivity.this, QuestionsActivity.class);
i.putExtra ("com.smartkidslovemaths.option", options);
startActivity (i);
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 ());
我打印出选项只是因为我想看看它是否有正确的东西。但是当我运行代码时,出现了NullPointerException
。现在我真的不知道为什么会这样。我试着把第二行改成
options = i.getExtras ().getParcelable ("options");
但结果仍然是一样的。我想我一定是在QuestionOptions
类中做错了什么,可能是因为我没有向packet写信,但有一个enum!没有名为writenum()的方法。
!那么,你能告诉我我做错了什么以及如何修复它吗?如果我做错了什么,也请告诉我
编辑:
这是我的日志:
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
执行该行时发生异常:
System.out.println (options.getDigitCount ());
我试过你的代码,问题似乎出在可包裹的对象上。 请更新以下内容,它将正常工作: 接受地块对象的构造函数
protected QuestionOptions(Parcel in) {
this.operationType = OperationType.valueOf(in.readString());
this.digitCount = in.readInt();
this.timerEnabled = in.readByte() != 0;
}
以及writeToParcel方法
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.operationType.name());
dest.writeInt(this.digitCount);
dest.writeByte((byte) (this.timerEnabled ? 1 : 0));
}
您可以通过以下方式从intent获取对象:
final QuestionOptions options = getIntent().getParcelableExtra("com.smartkidslovemaths.option");
我试过你的代码,问题似乎出在可包裹的对象上。 请更新以下内容,它将正常工作: 接受地块对象的构造函数
protected QuestionOptions(Parcel in) {
this.operationType = OperationType.valueOf(in.readString());
this.digitCount = in.readInt();
this.timerEnabled = in.readByte() != 0;
}
以及writeToParcel方法
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(this.operationType.name());
dest.writeInt(this.digitCount);
dest.writeByte((byte) (this.timerEnabled ? 1 : 0));
}
您可以通过以下方式从intent获取对象:
final QuestionOptions options = getIntent().getParcelableExtra("com.smartkidslovemaths.option");
张贴日志。NPE可以直接追溯到一行代码。@ChiefTwoPencils我添加了logcat,以及异常发生的确切位置checkout答案如果您对使用第三方库感到满意,请尝试使用事件总线@Poger,但我是否以正确的方式获取了内容?发布您的logcat。NPE可以直接追踪到一行代码。@ChiefTwoPencils我添加了logcat和异常发生的确切位置checkout答案如果您对使用第三方库感到满意,请尝试事件总线@Poger,但我得到的东西正确吗?太好了!还请注意,这里的写/读顺序很重要。。。以防将来需要更新对象。太好了!还请注意,这里的写/读顺序很重要。。。以防将来需要更新对象。