android - savedInstanceState 没有被恢复

Question

我刚开始使用 Android，我遇到了以下问题:

我正在尝试在打开新 Activity 时保存 InstanceState，并且我需要在 Activity 返回可见状态时恢复该状态。

这是我的 onSaveInstanceState 方法

@Override
public void onSaveInstanceState(Bundle outState) {
    super.onSaveInstanceState(outState);
    outState.putParcelableArrayList("movies", (ArrayList<Movie>) movies);

    Log.v("onSaveInstanceState ", "SAVING STATE");
    Log.v("Saving State", outState.toString());
}

这是我的 onCreate 方法，应该恢复之前保存的实例状态

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    if (savedInstanceState != null){
        Log.v("onCreate ", "EXISTING STATE");
        this.movies = savedInstanceState.getParcelableArrayList("movies");
    }else{
        Log.v("onCreate ", "EMPTY STATE");
    }

    setHasOptionsMenu(true);
}

如果您注意到，在 onSaveInstanceState 方法中，在我保存实例后，我对保存的实例执行 toString() ，它会向我显示包含我保存的值的完整实例。但是，当我恢复实例时，savedInstanceState 变量变为 null。

我正在使用一个自定义对象数组，其中每个对象都实现了 Parcelable。

下面是类:

public class Movie implements Parcelable {
private String title;
private String path;
private String overview;
private String releaseDate;
private double vote;

public Movie(String title, String overview, double vote, String releaseDate, String path) {
    this.title = title;
    this.overview = overview;
    this.vote = vote;
    this.releaseDate = releaseDate;
    this.path = path;
}

public String getTitle() {
    return title;
}

public String getPath() {
    return path;
}

public String getOverview() {
    return overview;
}

public String getReleaseDate() {
    return releaseDate;
}

public double getVote() {
    return vote;
}

protected Movie(Parcel source){
    this.title = source.readString();
    this.path = source.readString();
    this.overview = source.readString();
    this.releaseDate = source.readString();
    this.vote = source.readDouble();

}

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

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

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

@Override
public void writeToParcel(Parcel dest, int flags) {
    dest.writeString(title);
    dest.writeSerializable(path);
    dest.writeString(overview);
    dest.writeString(releaseDate);
    dest.writeDouble(vote);
}

@Override
public String toString() {
    return "Movie{" +
            "title='" + title + '\'' +
            ", path='" + path + '\'' +
            ", overview='" + overview + '\'' +
            ", releaseDate='" + releaseDate + '\'' +
            ", vote=" + vote +
            '}';
}

}

我觉得我以某种方式以错误的方式保存它。我遵循了有关如何执行此操作的教程。请让我知道我做错了什么。谢谢

Answer 1

我的问题通过添加到 list 文件中的 MainActivity 得到解决。

android:launchMode="singleTop"

创建了多个 Activity 实例，因此不会保存实例。