Question

我正在创建一个listview与checkbox的项目列表。我想将选中的选项传递给下一个activity。

为此，我使用字符串数组将结果传递给other activity。一切都很顺利但是当我点击按钮将数据传递给下一个活动时，应用程序停止时出现logcat错误NullPointerException。它可能是一个非常简单的概念，但我不知道它，因为我是android的新手。

任何帮助将不胜感激..

Java文件..

package com.example.travelplanner;

import java.util.ArrayList;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.util.Log;
import android.util.SparseBooleanArray;
import android.view.Menu;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.ListView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;

public class TailoredtwoActivity extends Activity implements OnItemClickListener, OnClickListener{

    String[] builder;
    Button btn1;
    ListView mListView;
    String[] array = new String[] {"Ham", "Turkey", "Bread"};

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

        ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_checked, array);

        mListView = (ListView) findViewById(R.id.listViewcity);
        mListView.setAdapter(adapter);
        mListView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);

        Button button = (Button) findViewById(R.id.btn_tailortwo_submit);
        button.setOnClickListener(this);
    }

    public void onClick(View view) {
        SparseBooleanArray positions = mListView.getCheckedItemPositions();
        for(int index = 0; index < array.length; index++) {
            if(positions.get(index)==true)
            {
                 builder[index] = array[index];
            }
        }
        Intent i1 = new Intent(this, TailoredthreeActivity.class);
        Bundle b = new Bundle();
        b.putStringArray("city", builder);
        i1.putExtras(b);
        startActivity(i1);
    }

    @Override
    public void onItemClick(AdapterView<?> arg0, View arg1, int arg2, long arg3) {
        // TODO Auto-generated method stub

    }
}

这是logcat：

07-12 10:48:49.686: E/AndroidRuntime(13047): FATAL EXCEPTION: main
07-12 10:48:49.686: E/AndroidRuntime(13047): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.travelplanner/com.example.travelplanner.TailoredthreeActivity}: java.lang.NullPointerException
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1967)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1992)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.app.ActivityThread.access$600(ActivityThread.java:127)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1158)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.os.Handler.dispatchMessage(Handler.java:99)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.os.Looper.loop(Looper.java:137)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.app.ActivityThread.main(ActivityThread.java:4448)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at java.lang.reflect.Method.invokeNative(Native Method)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at java.lang.reflect.Method.invoke(Method.java:511)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:823)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:590)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at dalvik.system.NativeStart.main(Native Method)
07-12 10:48:49.686: E/AndroidRuntime(13047): Caused by: java.lang.NullPointerException
07-12 10:48:49.686: E/AndroidRuntime(13047):    at com.example.travelplanner.TailoredthreeActivity.onCreate(TailoredthreeActivity.java:59)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.app.Activity.performCreate(Activity.java:4465)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1049)
07-12 10:48:49.686: E/AndroidRuntime(13047):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1931)
07-12 10:48:49.686: E/AndroidRuntime(13047):    ... 11 more

Answer 1

我建议您使用arraylist添加所选项目并将arraylist传递给第二个活动

   checked = new ArrayList<String>();
   public void onClick(View view) {
        SparseBooleanArray positions = mListView.getCheckedItemPositions();
        for(int index = 0; index < array.length; index++) {
            if(positions.get(index)==true)
            {
                 checked.add(array[index]);
            }
        }
        Intent i1 = new Intent(MainActivity.this, TailoredthreeActivity.class);
            i1.putStringArrayListExtra("list",checked);
        startActivity(i1);
    }

接收

 ArrayList<String> getChecked;   
 Bundle extras = getIntent().getExtras();
    if(extras!=null)
    {
      getChecked = extras.getStringArrayList("list");

   }

Answer 2

您需要首先初始化数组，因为每个数组都是java中的对象

public void onClick(View view) {
        SparseBooleanArray positions = mListView.getCheckedItemPositions();
         builder= new String[array.length];
        for(int index = 0; index < array.length; index++) {
            if(positions.get(index)==true)
            {
                 builder[index] = array[index];
            }
        }

将复选框数据传递给下一个活动

2 个答案: