Question

我使用newInstance方法初始化片段。然后我尝试在onCreate方法中获取参数。

public class ShowCostsFragment extends Fragment {
public static final String TAG = "ShowCostsFragment";

private static final String ARG_COSTS = "costs";

private List<Cost> mCosts;

public ShowCostsFragment() {
}

public static ShowCostsFragment newInstance(List<Cost> costs) {
    ShowCostsFragment fragment = new ShowCostsFragment();
    Bundle args = new Bundle();
    args.putParcelableArrayList(ARG_COSTS, (ArrayList<? extends Parcelable>) costs);
    fragment.setArguments(args);
    Log.d(TAG, "newInstance(). Costs size: " + costs.size());
    return fragment;
}

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    if (getArguments() != null) {
        mCosts = getArguments().getParcelableArrayList(ARG_COSTS);
        Log.d(TAG, "onCreate(). Costs size: " + mCosts.size());
    }
}

在MainActivity中，我运行此片段以显示一些数据。

private void startShowCostsFragment() {
    List<Cost> costs = mDBHelper.getAllCosts();
    Log.d(TAG, "startShowCostsFragment(). Costs size: " + costs.size());
    Fragment showCostsFragment = ShowCostsFragment.newInstance(costs);
    showFragment(showCostsFragment);
}

private void showFragment(Fragment fragment) {
    getSupportFragmentManager()
            .beginTransaction()
            .setCustomAnimations(android.R.anim.slide_in_left, android.R.anim.slide_out_right,
                    android.R.anim.slide_in_left, android.R.anim.slide_out_right)
            .replace(R.id.content_main, fragment)
            .addToBackStack(null)
            .commit();
}

当我运行方法startShowCostsFragment时，片段中的第二个和后续时间参数未正确设置。虽然新值已传递给方法，但mCosts列表不会更改其值。有时onCreate方法根本不会调用。当片段动态替换多次时，如何正确地将参数放入片段？

成本等级：

public class Cost implements Parcelable {
private int id;
private int value;
private String date;
private String description;
private List<Tag> tags = new ArrayList<>();

public Cost(int id, String date, int value, String description, List<Tag> tags) {
    this.id = id;
    this.value = value;
    this.date = date;
    this.description = description;
    this.tags = tags;
}

public Cost(int value, String date, String description, List<Tag> tags) {
    this.value = value;
    this.date = date;
    this.description = description;
    this.tags = tags;
}

public Cost() {

}

public int getId() {
    return id;
}

public int getValue() {
    return value;
}

public String getDate() {
    return date;
}

public String getDescription() {
    return description;
}

public List<Tag> getTags() {
    return tags;
}

public void setId(int id) {
    this.id = id;
}

public void setValue(int value) {
    this.value = value;
}

public void setDate(String date) {
    this.date = date;
}

public void setDescription(String description) {
    this.description = description;
}

public void setTags(List<Tag> tags) {
    this.tags = tags;
}

@Override
public int describeContents() {
    return 0;
}

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeInt(this.id);
    dest.writeInt(this.value);
    dest.writeString(this.date);
    dest.writeString(this.description);
    dest.writeTypedList(this.tags);
}

protected Cost(Parcel in) {
    this.id = in.readInt();
    this.value = in.readInt();
    this.date = in.readString();
    this.description = in.readString();
    this.tags = in.createTypedArrayList(Tag.CREATOR);
}

public static final Creator<Cost> CREATOR = new Creator<Cost>() {
    @Override
    public Cost createFromParcel(Parcel source) {
        return new Cost(source);
    }

    @Override
    public Cost[] newArray(int size) {
        return new Cost[size];
    }
};

}

Answer 1

Cost类必须实现Parcelable才能将其作为捆绑包发送。

编辑：

如果您的Cost班级正在实施Parcelable，那么您就不需要像(ArrayList<? extends Parcelable>) costs那样进行投射。你做演员，而不是实施。

public class Cost implement Parcelable {和实施。看看here。

片段参数未正确设置

1 个答案: