问题
I am getting a bit frustrated with an issue that I cannot seem to fully understand.
I have a listview with items and when I click them I want to pass an object (Parcelable) to a new activity. This is the code below:
lv_Entries.setOnItemClickListener(new AdapterView.OnItemClickListener() {
public void onItemClick(AdapterView<?> parent, View view, int position, long id) {
Intent getItchesScreen = new Intent(Home.this, Itches.class);
getItchesScreen.putExtra("i", 3);
Entry e = entries.get(position);
getItchesScreen.putExtra("entry", e);
startActivity(getItchesScreen);
}
});
Now, I have the "i" extra there for debugging purposes. I was just sending "entry" and when I got the intent on the activity it didn't work. Code below:
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_itches);
tv_date = (TextView) findViewById(R.id.tv_date);
Bundle b = getIntent().getExtras();
entry = b.getParcelable("entry");
tv_date.setText(entry.getDate());
itches = entry.getItches();
itchesAdapter = new ItchAdapter(this, itches);
ListView lv_Itches = (ListView) findViewById(R.id.lv_itches);
lv_Itches.setAdapter(itchesAdapter);
}
So when I read my bundle there is nothing at all. No "entry" key and no "i" key (I debugged to read i using watch feature)
BUT! If I don't send "entry" and only send "i" and I debug to catch "i" I do get it!
I have no idea why sending entry is ruining things but I cannot find any answer. I debugged the object and it does find it though .get(position).
Hope anyone can give me any ideas, and sorry for any trouble.
EDIT
Below is the code for Entry:
public class Entry implements Parcelable{
private String date;
private ArrayList<Itch> itches;
public Entry(String date){
this.date = date;
itches = new ArrayList<Itch>();
}
// PARCELABLE
public Entry(Parcel source){
date = source.readString();
source.readTypedList(itches, Itch.CREATOR);
}
public void AddItch(Itch itch){
itches.add(itch);
}
// get intensity average for the itches
public int IntensityAverage(){
int intensity = 0;
for(Itch i : itches){
intensity += i.getIntensity();
}
return intensity/itches.size();
}
public String getDate() {
return date;
}
public void setDate(String date) {
this.date = date;
}
public ArrayList<Itch> getItches() {
return itches;
}
public void setItches(ArrayList<Itch> itches) {
this.itches = itches;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(date);
dest.writeTypedList(itches);
}
public static final Parcelable.Creator<Entry> CREATOR =
new Parcelable.Creator<Entry>() {
public Entry createFromParcel(Parcel source) {
return new Entry(source);
}
public Entry[] newArray(int size) {
return new Entry[size];
}
};
}
Itch class is also Parceable. I am populating correctly (no crashes on Android at least) the ListView with it.
For convenience I place the code here aswell:
public class Itch implements Parcelable{
private String time;
private String local;
private int intensity;
public Itch(String time, String local, int intensity){
this.time = time;
this.local = local;
this.intensity = intensity;
}
// PARCELABLE
public Itch(Parcel source){
time = source.readString();
local = source.readString();
intensity = source.readInt();
}
public String getTime() {
return time;
}
public void setTime(String time) {
this.time = time;
}
public String getLocal() {
return local;
}
public void setLocal(String local) {
this.local = local;
}
public int getIntensity() {
return intensity;
}
public void setIntensity(int intensity) {
this.intensity = intensity;
}
@Override
public int describeContents() {
return 0;
}
@Override
public void writeToParcel(Parcel dest, int flags) {
dest.writeString(time);
dest.writeString(local);
dest.writeInt(intensity);
}
public static final Parcelable.Creator<Itch> CREATOR =
new Parcelable.Creator<Itch>() {
public Itch createFromParcel(Parcel source) {
return new Itch(source);
}
public Itch[] newArray(int size) {
return new Itch[size];
}
};
}
回答1:
Alright so... What was the problem? Simple.
The reason why the parcelable always came out null was because a stupid error was occurring. Which error?
Well, okay so take a look at this piece of code:
entry = b.getParcelable("entry");
What is it saying? It is saying that entry will be equal to the parcelable "entry" key. But what does that really mean? Look at entry constructor.
// PARCELABLE
public Entry(Parcel source){
date = source.readString();
source.readTypedList(itches, Itch.CREATOR);
}
So when you say that entry is equals to a parcelable, then you will call this constructor in the Entry class that I have posted. But why is it wrong you might ask?
Well, so take a look. We're giving ArrayList itches to the method readTypeList. but... wait a second. If that is a constructor that means that we're building from 0... So... is itches initiated? No it is not! Because I was only initiating itches in the "normal" constructor!
public Entry(String date){
this.date = date;
itches = new ArrayList<Itch>();
}
So the solution is...
// PARCELABLE
public Entry(Parcel source){
date = source.readString();
//add this if condition!
if (itches == null) {
itches = new ArrayList<Itch>();
}
source.readTypedList(itches, Itch.CREATOR);
}
And thats it. That fixes our problem! :)
If other error occurs please be aware: Make SURE that your key is correct. So check out for any typos in your getting extras.
entry = b.getParcelable("entyr");
as instead of
entry = b.getParcelable("entry");
And any other type of error like that.
That is not a good practive, you should have a variable that has the "entry" written on it so you never have this type of error mistakes. I have it in my code because I am fast-programming to build up a prototype :)
Happy coding!
回答2:
have you tried doing this in onCreate()
Intent i = getIntent();
if(i.hasExtra("entry")){
entry = i.getParcelableExtra("entry");
}else{
Log.v("EXTRAS", "entry not found");
}
来源：https://stackoverflow.com/questions/25000008/extra-with-parcelable-comes-out-null-but-without-its-fine