java Android，如何在 Parcelable 类中正确使用 readTypedList 方法？
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Android, How to use readTypedList method correctly in a Parcelable class?
提问by Gen
I have two Activities, in the first one, I instanciate an ArrayList of Object myObject. In the second activity, i need to get this Arraylist. I've found a tutorial : http://prasanta-paul.blogspot.com/2010/06/android-parcelable-example.htmlI have implemented my class liked it's explain.
我有两个活动，在第一个活动中，我实例化了对象 myObject 的 ArrayList。在第二个活动中，我需要获取这个 Arraylist。我找到了一个教程：http: //prasanta-paul.blogspot.com/2010/06/android-parcelable-example.html我已经实现了我的课程，喜欢它的解释。
public class Chapitre implements Parcelable{
公共类 Chapitre 实现 Parcelable{
private int numero;
private String titre;
private String description;
private int nbVideo;
private ArrayList<Video> listeVideo;
public Chapitre(int numero, String titre, String description,
ArrayList<Video> listeVideo) {
this.numero = numero;
this.titre = titre;
this.description = description;
this.listeVideo = listeVideo;
this.nbVideo = listeVideo.size();
}
//Getters and Setters ...
private Chapitre(Parcel source) {
numero = source.readInt();
titre = source.readString();
description = source.readString();
nbVideo = source.readInt();
source.readTypedList(listeVideo, Video.CREATOR);
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(numero);
dest.writeString(titre);
dest.writeString(description);
dest.writeInt(nbVideo);
dest.writeTypedList(listeVideo);
}
public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {
public Chapitre createFromParcel(Parcel in) {
return new Chapitre(in);
}
public Chapitre[] newArray(int size) {
return new Chapitre[size];
}
};
}
}
public class Video implements Parcelable{
公共类视频实现 Parcelable{
private String titre;
private int numero;
private String url;
private String description;
private String imageUrl;
private Bitmap image;
private String duree;
/**
*
* @param nom
* @param numero
* @param url
* @param description
*/
public Video(String titre, String url, String description) {
super();
this.titre = titre;
this.url = url;
this.description = description;
}
public Video(int numero, String titre, String url, String description) {
super();
this.titre = titre;
this.url = url;
this.description = description;
this.numero = numero;
}
public Video(String titre,int numero, String url, String description, String imageUrl) {
super();
this.titre = titre;
this.url = url;
this.description = description;
this.imageUrl = imageUrl;
this.numero = numero;
setImage(fetchImage(imageUrl));
}
//Getters and Setters ...
@Override
public int describeContents() {
// TODO Auto-generated method stub
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(titre);
dest.writeInt(numero);
dest.writeString(url);
dest.writeString(description);
dest.writeString(imageUrl);
dest.writeString(duree);
}
public Video(Parcel source){
/*
* Reconstruct from the Parcel
*/
Log.v("TAG", "ParcelData(Parcel source): time to put back parcel data");
titre = source.readString();
numero = source.readInt();
url = source.readString();
description = source.readString();
imageUrl = source.readString();
duree = source.readString();
}
public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {
public Video createFromParcel(Parcel in) {
return new Video(in);
}
public Video[] newArray(int size) {
return new Video[size];
}
};
}
}
But I get nullPointException on the line "source.readTypedList(listeVideo, Video.CREATOR);" in the class Chapitre.
但是我在“source.readTypedList(listeVideo, Video.CREATOR);”这一行得到了 nullPointException 在课堂上。
07-21 10:07:28.212: ERROR/AndroidRuntime(682): FATAL EXCEPTION: main
07-21 10:07:28.212: ERROR/AndroidRuntime(682): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.genicorp.video.proto/com.genicorp.video.proto.Lecture}: java.lang.NullPointerException
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1736)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1752)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.app.ActivityThread.access00(ActivityThread.java:123)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:993)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Handler.dispatchMessage(Handler.java:99)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Looper.loop(Looper.java:126)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.app.ActivityThread.main(ActivityThread.java:3997)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at java.lang.reflect.Method.invokeNative(Native Method)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at java.lang.reflect.Method.invoke(Method.java:491)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:841)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:599)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at dalvik.system.NativeStart.main(Native Method)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): Caused by: java.lang.NullPointerException
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Parcel.readTypedList(Parcel.java:1630)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at com.genicorp.video.proto.Chapitre.<init>(Chapitre.java:70)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at com.genicorp.video.proto.Chapitre.<init>(Chapitre.java:65)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at com.genicorp.video.proto.Chapitre.createFromParcel(Chapitre.java:89)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at com.genicorp.video.proto.Chapitre.createFromParcel(Chapitre.java:1)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Parcel.readParcelable(Parcel.java:1981)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Parcel.readValue(Parcel.java:1846)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Parcel.readListInternal(Parcel.java:2092)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Parcel.readArrayList(Parcel.java:1536)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Parcel.readValue(Parcel.java:1867)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Parcel.readMapInternal(Parcel.java:2083)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Bundle.unparcel(Bundle.java:215)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.os.Bundle.getParcelableArrayList(Bundle.java:1151)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.content.Intent.getParcelableArrayListExtra(Intent.java:3634)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at com.genicorp.video.proto.Lecture.onCreate(Lecture.java:37)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1048)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1700)
07-21 10:07:28.212: ERROR/AndroidRuntime(682): ... 11 more
I've already waste 1 day on this, so if anyone could help me, it would be great,
我已经在这上面浪费了 1 天，所以如果有人可以帮助我，那就太好了，
Thanks in advance
提前致谢
回答by SBerg413
Hopefully, you've figured this out by now. But for anyone else who stumbles upon this one. The NullPointerException you were getting was caused by the ArrayList never being initialized.
希望你现在已经明白了这一点。但对于任何偶然发现这一点的人来说。您得到的 NullPointerException 是由从未初始化的 ArrayList 引起的。
This would fix it:
这将解决它：
private Chapitre(){
listVideo = new ArrayList<Video>();
}
private Chapitre(Parcel source) {
// Call the above constructor
this();
numero = source.readInt();
titre = source.readString();
description = source.readString();
nbVideo = source.readInt();
source.readTypedList(listeVideo, Video.CREATOR);
}
回答by shaobin0604
Another solution: use createTypedArrayListinstead of readTypedListwhich requires a non-nullList object reference
另一种解决方案：使用createTypedArrayList代替readTypedListwhich 需要一个非空的List 对象引用
回答by IxDay
Also keep in mind that you have to read and write parcelable object attribute in the same order! I also 2 hours because the unmarshalling was not in the same order of the marshalling.
还要记住，您必须以相同的顺序读取和写入 Parcelable 对象属性！我也是 2 小时，因为解组与编组的顺序不同。
回答by Mike Jancola
Also consider initializing the object with an immutable empty list.
还可以考虑使用不可变的空列表初始化对象。
private ArrayList<Video> listevideo = Collections.emptyList()
private ArrayList<Video> listevideo = Collections.emptyList()
More details here: Collections.emptyList() vs. new instance
此处有更多详细信息：Collections.emptyList() 与新实例
