是否可以在 Android 上创建可 Parcelable 的 HashMap？

Question

我试图将 HashMap 扩展为 Parcelable，并且获得了要编译的语法，但是，在运行时它会抛出异常并返回一个空指针，试图对数据进行解组。

发送者必须转换为 (Parcelable) 来解决歧义，然而，接收者抱怨期望是 Parcelable，但却发现了 HashMap。

有人在这方面取得过成功吗？ 我的语法错误吗？ 有更好的解决方案吗？

以下是代码：

• HomeActivity.java - 发送方
• ContentViewActivity.java - 接收方
• ContentItemSimple.java - 正如其名称 暗示（包装字符串和整数）
• ContentItemCollection.java - 这是 HashMap

HomeActivity.java

package com.mobibob.android.studyparceable;

import java.util.HashMap;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.os.Parcel;
import android.os.Parcelable;
import android.text.format.Time;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class HomeActivity extends Activity implements OnClickListener {
    private static final String TAG = "HomeActivity";
    private ContentItemSimple mContentItemSimple = null;
    private ContentItemContainer mContentItemContainer = null;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.home);

        Button click = (Button) findViewById(R.id.button_clickit);
        click.setOnClickListener(this);

        mContentItemSimple = new ContentItemSimple();
        mContentItemSimple.name = "mobibob";
        mContentItemSimple.year = 2010;

        String value = "value";
        Time nowTime = new Time();
        nowTime.setToNow();
        mContentItemContainer = new ContentItemContainer();
        mContentItemContainer.put("string", new String("baseball is great!"));
        mContentItemContainer.put("integer", new Integer(1234));
//        mContentItemContainer.put("boolean", new Boolean(true));
//        mContentItemContainer.put("date", nowTime);
//        mContentItemContainer.put("parcel", new Bundle());
        Log.d(TAG, "..... " + mContentItemContainer.toString());
    }

    @Override
    public void onClick(View v) {

        Intent i = new Intent(getBaseContext(), ContentViewActivity.class);
        i.putExtra(ContentItemSimple.EXTRA_CONTENT_DETAIL, mContentItemSimple);
        i.putExtra(ContentItemContainer.EXTRA_CONTENT_CONTAINER, (Parcelable) mContentItemContainer);
        startActivityForResult(i, 0);

    }
}

ContentViewActivity

package com.mobibob.android.studyparceable;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.TextView;

import com.mobibob.android.studyparceable.ContentItemSimple;

public class ContentViewActivity extends Activity implements OnClickListener {

    private static final String TAG = "ContentViewActivity";

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

        setContentView(R.layout.content_view);

        Button gohome = (Button) findViewById(R.id.button_gohome);

        gohome.setOnClickListener(this);

        ContentItemSimple ci = null;
        ContentItemContainer cx = null;

        try {
            ci = getIntent().getParcelableExtra(ContentItemSimple.EXTRA_CONTENT_DETAIL);
            Log.i(TAG, "ci = " + ci.toString());

            cx = getIntent().getParcelableExtra(ContentItemContainer.EXTRA_CONTENT_CONTAINER);
            Log.i(TAG, "cx = " + cx.toString());

            TextView tvName = (TextView) findViewById(R.id.ci_name);
            tvName.setText(ci.name);
            TextView tvYear = (TextView) findViewById(R.id.ci_year);
            tvYear.setText(String.format("%d", ci.year));

        } catch (Exception e) {
            Log.e(TAG, e.toString());
            e.printStackTrace();
        }
    }

    @Override
    public void onClick(View v) {
        finish();
    }

}

ContentItemSimple.java

package com.mobibob.android.studyparceable;

import android.os.Parcel;
import android.os.Parcelable;
import android.util.Log;

public class ContentItemSimple implements Parcelable {
        public static final String TAG = "ContentItem";
    public static final String EXTRA_CONTENT_DETAIL = "contentDetail";
    public String name = "name";
    public Integer year = Integer.MIN_VALUE;

    ContentItemSimple() {
        name = new String("");
        year = new Integer(Integer.MIN_VALUE);
    }

    ContentItemSimple(Parcel in) {
            try {
                name = in.readString();
                year = in.readInt();
            } catch (Exception e) {
                Log.e(TAG, e.toString());
                e.printStackTrace();
        }
    }

    @Override
    public String toString() {
        return String.format("name=%s age=%d", name, year);
    }

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeString(name);
        dest.writeInt(year);
    }

    public static final Parcelable.Creator<ContentItemSimple> CREATOR = new Parcelable.Creator<ContentItemSimple>() {
        public ContentItemSimple createFromParcel(Parcel in) {
        return new ContentItemSimple(in);
        }

        public ContentItemSimple[] newArray(int size) {
        return new ContentItemSimple[size];
        }
    };

}

ContentItemContainer.java

package com.mobibob.android.studyparceable;

import java.util.HashMap;
import java.util.Iterator;

import android.os.Parcel;
import android.os.Parcelable;

public class ContentItemContainer extends HashMap<String, Object> implements Parcelable {
    /**
     * Container for wddx 'struct' elements.
     */
    private static final long serialVersionUID = 1L;
    // public String name = "?";
    // public String value = "?";
    public static final String EXTRA_CONTENT_DETAIL = "contentDetail";
    public static final String EXTRA_CONTENT_CONTAINER = "contentContainer";
    public static final String EXTRA_CONTENTDETAIL_NAME = "name";
    public static final String EXTRA_CONTENTDETAIL_VALUE = "value";

//    private static HashMap<String, Object> map = new HashMap<String, Object>();

    ContentItemContainer() {
        super();
    }

    ContentItemContainer(Parcel in) {
        in.readMap(this, ContentItemContainer.class.getClassLoader());
    }

    @Override
    public String toString() {
        StringBuilder sb = new StringBuilder("");
        Integer x = 0;
        Iterator<HashMap.Entry<String, Object>> it = this.entrySet().iterator();
        while (it.hasNext()) {
            HashMap.Entry<String, Object> pairs = (HashMap.Entry<String, Object>) it.next();
            x++;
            sb.append("\n"+x.toString()+": ").append("name=").append(pairs.getKey()).append(" value=").append(pairs.getValue().toString());
        }
        return sb.toString();
    }

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

    @Override
    public void writeToParcel(Parcel dest, int flags) {
        dest.writeMap(this);
    }

    public static final Parcelable.Creator<ContentItemContainer> CREATOR = new Parcelable.Creator<ContentItemContainer>() {
        public ContentItemContainer createFromParcel(Parcel in) {
            return new ContentItemContainer(in);
        }

        public ContentItemContainer[] newArray(int size) {
            return new ContentItemContainer[size];
        }
    };

}

Answer 1

ContentItemContainer 类的实现方式 - 作为扩展 HashMap，您的 writeToParcel 和 Parcelable.Creator 将永远不会被调用。

原因是 Map 是放入 Parcel 中的有效数据类型，因此该类会使用 HashMap 类的逻辑（而不是您的逻辑）进行扁平化。这是因为 Parcel 的实现方式会检查提供的值是否是特定顺序的某些类的后代。

当解包额外内容时，将根据对象的数据创建一个 HashMap。

要解决此问题，您可以将 HashMap 隐藏在类中，并公开 HashMap 的 getters/putters。这与 ContentValues 的实现方式完全相同，并且打包/解包它工作没有任何问题。