java可分块数组对象列表

Question

我试图将Person对象的ArrayList从MainActivity传递到SecondActivity，以便在自定义listView适配器中打印Person的详细信息

应用程序运行，但在通过人员的ArrayList后到达第二个活动的startActivity()时崩溃

Person实现Parcelable

public Person(String id, String name) {
    this.id = id;
    this.name = name;
}

public Person(Parcel in) {
    id = in.readString();
    name = in.readString();
}

public void writeToParcel(Parcel out, int flags) {
    out.writeString(id);
    out.writeString(name);
}

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

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

主要活动

List<Person> list = new ArrayList<Person>();

public void onButtonClick() {
    Intent intent = new Intent(getApplicationContext(), SecondActivity.class);
    intent.putExtra("personObject", list);
    startActivity(intent);
}

二等活动

protected void onCreate() {
    Intent i = getIntent();
    ArrayList<Person> person = (ArrayList<Person>) i.getParcelableExtra("personObject");

    //Get the Arraylist of Persons from MainActivity 
    listView.setAdapter(new personAdapter(this, R.layout.person_list_layout, person));

编辑：堆栈错误跟踪

E/AndroidRuntime(16698): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.testApp/com.example.testApp.SecondActivity}: java.lang.NullPointerException
E/AndroidRuntime(16698):    at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2212)
E/AndroidRuntime(16698):    at 安卓.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2271)
E/AndroidRuntime(16698):    at 安卓.app.ActivityThread.access$800(ActivityThread.java:144)
E/AndroidRuntime(16698):    at 安卓.app.ActivityThread$H.handleMessage(ActivityThread.java:1205)
E/AndroidRuntime(16698):    at 安卓.os.Handler.dispatchMessage(Handler.java:102)
E/AndroidRuntime(16698):    at 安卓.os.Looper.loop(Looper.java:136)
E/AndroidRuntime(16698):    at 安卓.app.ActivityThread.main(ActivityThread.java:5146)
E/AndroidRuntime(16698):    at java.lang.reflect.Method.invokeNative(Native Method)
E/AndroidRuntime(16698):    at java.lang.reflect.Method.invoke(Method.java:515)
E/AndroidRuntime(16698):    at com.安卓.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:732)
E/AndroidRuntime(16698):    at com.安卓.internal.os.ZygoteInit.main(ZygoteInit.java:566)
E/AndroidRuntime(16698):    at dalvik.system.NativeStart.main(Native Method)
E/AndroidRuntime(16698): Caused by: java.lang.NullPointerException
E/AndroidRuntime(16698):    at com.example.testApp.SecondActivity.onCreate(SecondActivity.java:35)
E/AndroidRuntime(16698):    at 安卓.app.Activity.performCreate(Activity.java:5231)
E/AndroidRuntime(16698):    at 安卓.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
E/AndroidRuntime(16698):    at 安卓.app.ActivityThread.performLaunchActivity(ActivityThread.java:2169)

EDIT2:错误日志第35行

listView.setAdapter(new personAdapter(this, R.layout.person_list_layout, person));

Answer 1

你应该使用另一个函数：intent.putParcelableArrayListExtra(String name, ArrayList<? extends Parcelable> value)Google site在main Activity中，然后intent.getParcelableArrayListExtra进入第二个Activity。 希望这有帮助

Answer 2

ArrayList不实现Parcelable，但它实现了Serializable，因此不能使用getParcelableExtra来接收数据，必须使用getSerializableExtra

ArrayList<Person> person = (ArrayList<Person>) i.getSerializableExtra("personObject");

Person类也必须实现Serializable，下面是代码示例：

Person implements Serializable{
   private static final long serialVersionUID = 0L;
   String id;
   String name;
}

更新：

另一种解决方案：使用putParcelableArrayListExtra和getParcelableArrayListExtra

第一项活动：

ArrayList<Person> list = new ArrayList<Person>();

public void onButtonClick() {
    Intent intent = new Intent(getApplicationContext(), SecondActivity.class);
    intent.putParcelableArrayListExtra("personObject", list);
    startActivity(intent);
}

第二项活动：

ArrayList<Person> person = (ArrayList<Person>) i.getParcelableArrayListExtra("personObject");

注意：Parcelable比Serializable快，所以如果想要传递大量数据，第二种解决方案更好

Answer 3

一,。用一个按钮创建FirstActivity

package com.appkart.sdcardconnection;

import java.util.ArrayList;

import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;

public class FirstActivity extends ActionBarActivity {

    private Button btn;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.first_activity);

        btn = (Button) findViewById(R.id.btn);
        btn.setOnClickListener(new OnClickListener() {

            @Override
            public void onClick(View v) {
                Intent intent = new Intent(FirstActivity.this, SecondActivity.class);
                ArrayList<Person> personList = new ArrayList<Person>();

                personList.add(new Person("10", "Arun"));
                personList.add(new Person("20", "Ankit"));          

                intent.putExtra("person_list", personList);
                startActivity(intent);              
            }
        });
    }
}

二,。xml文件

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:paddingBottom="@dimen/activity_vertical_margin"
    android:paddingLeft="@dimen/activity_horizontal_margin"
    android:paddingRight="@dimen/activity_horizontal_margin"
    android:paddingTop="@dimen/activity_vertical_margin"
    tools:context="com.appkart.sdcardconnection.FirstActivity" >

    <Button
        android:id="@+id/btn"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Second Activity" />

</RelativeLayout>

三,。第二项活动

package com.appkart.sdcardconnection;

import java.util.ArrayList;
import java.util.List;

import android.app.Activity;
import android.os.Bundle;
import android.util.Log;

public class SecondActivity extends Activity {

    private static final String TAG = SecondActivity.class.getSimpleName();

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.second_activity);

        List<Person> personList = (ArrayList<Person>) getIntent()
                .getSerializableExtra("person_list");

        for (Person person : personList) {
            Log.d(TAG, "id  : " + person.getId());
            Log.d(TAG, "name  : " + person.getName());

        }
    }
}

四,。波乔

package com.appkart.sdcardconnection;

import java.io.Serializable;

public class Person implements Serializable {

    private String id;
    private String name;

    public Person(String id, String name) {
        this.id = id;
        this.name = name;
    }

    public String getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

使用Serializable代替Parcelable。根据ArrayList java文档，它实现了可序列化Array list java doc