android - 为什么可打包对象在接收 Activity 中为空？

Question

我遵循 Android 开发人员指南中的 Parcelable 示例，目的是将一个更复杂的对象发送到不同的 Activity 。现在，我的类是 String 成员的包装器。如果我将对象放入 Intent 中并从 Intent 中读回它，它会按预期读取，但是，在接收方，它始终是空指针。

我的类(class):

package com.mobibob.android.myapp;

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


public class ContentItem implements Parcelable {
    public String name = "name";
    public static final String EXTRA_CONTENT_DETAIL = "contentDetail";

    ContentItem(String n) {
        name = n;
    }

    ContentItem(Parcel in) {
            in.readParcelable(ContentItem.class.getClassLoader());  <--- NEW CODE
        name = in.readString();
    }

    @Override
    public String toString() {
        return name.toString();
    }

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

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

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

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

}

我的 Intent/回读/startActivity 设置:

    ContentItem ci = new ContentItem("mobibob");
// Launch ...
Intent i = new Intent(getApplicationContext(), ContentDetailActivity.class);
i.putExtra(ContentItem.EXTRA_CONTENT_DETAIL, ci);
ContentItem readbackCi = i.getParcelableExtra(ContentItem.EXTRA_CONTENT_DETAIL);
Log.d(TAG, "\n\n\t" + readbackCi.name);
startActivity(i);

我的接收 Activity :

package com.mobibob.android.myapp;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.util.Log;
import android.widget.TextView;

public class ContentDetailActivity extends Activity {

    public static final String TAG = "ContentDetailActivity";

    @Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
        setContentView(R.layout.content_detail);

        try {
            Intent i = getIntent();
            Log.d(TAG, "intent: " + i.toString());
            Log.d(TAG, "extras: " + i.getExtras());

            ContentItem ci = (ContentItem) i.getParcelableExtra(ContentItem.EXTRA_CONTENT_DETAIL);

            Log.d(TAG, "content-item: " + ci.toString());

            ((TextView) findViewById(R.id.name_of_content)).setText(ci.name);

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

}

我的日志:

08-16 15:03:40.121 I/HomeActivity( 9840): onItemClick - AdapterView (pos=1 id=1)
08-16 15:03:40.121 D/HomeActivity( 9840): 
08-16 15:03:40.121 D/HomeActivity( 9840): 
08-16 15:03:40.121 D/HomeActivity( 9840):   Rock/Pop
08-16 15:03:40.131 I/ActivityManager( 1186): Starting activity: Intent { cmp=com.mobibob.android.myapp/.ContentDetailActivity (has extras) }
08-16 15:03:40.341 D/ContentDetailActivity( 9840): intent: Intent { cmp=com.mobibob.android.myapp/.ContentDetailActivity (has extras) }
08-16 15:03:40.341 D/ContentDetailActivity( 9840): extras: Bundle[mParcelledData.dataSize=148]
08-16 15:03:40.351 D/ContentDetailActivity( 9840): java.lang.NullPointerException
08-16 15:03:40.653 I/ActivityManager( 1186): Displayed activity com.mobibob.android.myapp/.ContentDetailActivity: 336 ms (total 336 ms)

我的堆栈回溯:

08-16 17:19:52.170 I/HomeActivity( 3147): onItemClick - AdapterView (pos=3 id=3)
08-16 17:19:52.170 D/HomeActivity( 3147): 
08-16 17:19:52.170 D/HomeActivity( 3147): 
08-16 17:19:52.170 D/HomeActivity( 3147):   mobibob
08-16 17:19:52.170 I/ActivityManager( 1202): Starting activity: Intent { cmp=com.mobibob.android.myapp/.ContentDetailActivity (has extras) }
08-16 17:19:52.410 D/ContentDetailActivity( 3147): intent: Intent { cmp=com.mobibob.android.myapp/.ContentDetailActivity (has extras) }
08-16 17:19:52.410 D/ContentDetailActivity( 3147): extras: Bundle[mParcelledData.dataSize=144]
08-16 17:19:52.410 D/ContentDetailActivity( 3147): java.lang.NullPointerException
08-16 17:19:52.410 W/System.err( 3147): java.lang.NullPointerException
08-16 17:19:52.420 W/System.err( 3147):     at java.lang.reflect.Field.getField(Native Method)
08-16 17:19:52.420 W/System.err( 3147):     at java.lang.reflect.Field.get(Field.java:247)
08-16 17:19:52.420 W/System.err( 3147):     at android.os.Parcel.readParcelable(Parcel.java:1811)
08-16 17:19:52.420 W/System.err( 3147):     at android.os.Parcel.readValue(Parcel.java:1713)
08-16 17:19:52.420 W/System.err( 3147):     at android.os.Parcel.readMapInternal(Parcel.java:1947)
08-16 17:19:52.420 W/System.err( 3147):     at android.os.Bundle.unparcel(Bundle.java:169)
08-16 17:19:52.420 W/System.err( 3147):     at android.os.Bundle.getParcelable(Bundle.java:1037)
08-16 17:19:52.430 W/System.err( 3147):     at android.content.Intent.getParcelableExtra(Intent.java:3276)
08-16 17:19:52.430 W/System.err( 3147):     at com.mobibob.android.myapp.ContentDetailActivity.onCreate(ContentDetailActivity.java:24)
08-16 17:19:52.430 W/System.err( 3147):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047)
08-16 17:19:52.430 W/System.err( 3147):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2459)
08-16 17:19:52.430 W/System.err( 3147):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2512)
08-16 17:19:52.430 W/System.err( 3147):     at android.app.ActivityThread.access$2200(ActivityThread.java:119)
08-16 17:19:52.430 W/System.err( 3147):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1863)
08-16 17:19:52.430 W/System.err( 3147):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-16 17:19:52.430 W/System.err( 3147):     at android.os.Looper.loop(Looper.java:123)
08-16 17:19:52.430 W/System.err( 3147):     at android.app.ActivityThread.main(ActivityThread.java:4363)
08-16 17:19:52.430 W/System.err( 3147):     at java.lang.reflect.Method.invokeNative(Native Method)
08-16 17:19:52.430 W/System.err( 3147):     at java.lang.reflect.Method.invoke(Method.java:521)
08-16 17:19:52.430 W/System.err( 3147):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
08-16 17:19:52.430 W/System.err( 3147):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
08-16 17:19:52.440 W/System.err( 3147):     at dalvik.system.NativeStart.main(Native Method)
08-16 17:19:52.895 I/ActivityManager( 1202): Displayed activity com.mobibob.android.myapp/.ContentDetailActivity: 582 ms (total 582 ms)

Answer 1

我猜 in.readParcelable(ContentItem.class.getClassLoader()); 已经返回了您重新创建的 ContentItem。因此，您应该将该行放入 Parcelable.Creator 的 createFromParcel-Method 中。不过只是猜测。