错误，当我想从另一个列表创建一个列表视图

Question

我有两个类。在第一个类ListDataActivityInterv中，我想显示类ListViewMultipleSelectionActivity中的所有项目。所以我在第一节课，当我按下按钮添加我想要显示一个列表视图（第二课），检查一，两个项目，当我按发送按钮出现在第一课。另外我想将这些项目存储在表格中。这里是我的第一类代码：

public class ListDataActivityInterv extends Activity{ 

    private ListView lsInterventiiView = null; 
    private PacientiDB pacientiDB = null; 
    private PacientiAdapter adapter = null; 
    private ArrayList<Interventii> listInterventii = null; 
    private Button buttonCreate2 = null; 
    private String text = null; 

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

     text = getIntent().getExtras().getString("Pacienti"); 
     TextView textView1 = (TextView) findViewById(R.id.textView2); 
     textView1.setText(text); 

     buttonCreate2 = (Button) findViewById(R.id.btnCreateInt); 
     buttonCreate2.setOnClickListener(new OnClickListener() { 

      @Override 
       public void onClick(View v) { 
        Intent intent = new Intent(ListDataActivityInterv.this, ListViewMultipleSelectionActivity.class); 
        startActivity(intent); 
       } 
     }); 

      Bundle b = getIntent().getExtras();   
      String[] resultArr = b.getStringArray("selectedItems");  
      ListView lv = (ListView) findViewById(R.id.lsvListInterventii);   
      ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, resultArr);   
      lv.setAdapter(adapter); 
        } 

} 

第二类：

public class ListViewMultipleSelectionActivity extends Activity implements 
     OnClickListener { 
     Button button; 
     ListView listView;  
     ArrayAdapter<String> adapter; 
     public String text = null; 
     private PacientiDB pacientiDB = null; 

     /** Called when the activity is first created. */  
     @Override  
     public void onCreate(Bundle savedInstanceState) {  
      super.onCreate(savedInstanceState);   
      setContentView(R.layout.maincheckinterv); 
      text = getIntent().getExtras().getString("Pacienti"); 
      TextView text1 = (TextView) findViewById(R.id.textViewListInter); 
      text1.setText(text); 
      findViewsById();   
      String[] sports = getResources().getStringArray(R.array.sports_array);  
      adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_multiple_choice, sports);  
      listView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE);  
      listView.setAdapter(adapter);   
      button.setOnClickListener(this); }  

     private void findViewsById() {   
      listView = (ListView) findViewById(R.id.list);  
      button = (Button) findViewById(R.id.testbutton); }  

     public void onClick(View v) {  
      Interventii interventie = pacientiDB.getInterv(text); 
      SparseBooleanArray checked = listView.getCheckedItemPositions();  
      ArrayList<String> selectedItems = new ArrayList<String>();   
      for (int i = 0; i < checked.size(); i++) {   

       int position = checked.keyAt(i);    

       if (checked.valueAt(i))     
        selectedItems.add(adapter.getItem(position));  }  
      String[] outputStrArr = new String[selectedItems.size()];   
      for (int i = 0; i < selectedItems.size(); i++) {   
       outputStrArr[i] = selectedItems.get(i); 
       interventie = new Interventii(); 
       interventie.setDenumire(selectedItems.get(i)); 
       pacientiDB.insertI(interventie); 
       }   
      Intent intent = new Intent(getApplicationContext(), ListDataActivityInterv.class);     
      Bundle b = new Bundle();  
      b.putStringArray("selectedItems", outputStrArr);    
      intent.putExtras(b);    
      startActivity(intent); } 
     } 

我收到此错误：

04-30 19:42:55.642: E/AndroidRuntime(4899): FATAL EXCEPTION: main 
04-30 19:42:55.642: E/AndroidRuntime(4899): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.medicaldoi/com.example.medicaldoi.ListDataActivityInterv}: java.lang.NullPointerException 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2663) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2679) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.app.ActivityThread.access$2300(ActivityThread.java:125) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2033) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.os.Handler.dispatchMessage(Handler.java:99) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.os.Looper.loop(Looper.java:123) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.app.ActivityThread.main(ActivityThread.java:4627) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at java.lang.reflect.Method.invokeNative(Native Method) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at java.lang.reflect.Method.invoke(Method.java:521) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at dalvik.system.NativeStart.main(Native Method) 
04-30 19:42:55.642: E/AndroidRuntime(4899): Caused by: java.lang.NullPointerException 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at java.util.Arrays$ArrayList.<init>(Arrays.java:49) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at java.util.Arrays.asList(Arrays.java:171) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.widget.ArrayAdapter.<init>(ArrayAdapter.java:125) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at com.example.medicaldoi.ListDataActivityInterv.onCreate(ListDataActivityInterv.java:45) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1047) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2627) 
04-30 19:42:55.642: E/AndroidRuntime(4899):  ... 11 more 

有人能帮助我吗？有人有另一个想法？

Answer 1

使用下面的类，ListDataActivityInterv

package com.pranav.listviewdemo; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.ArrayAdapter; 
import android.widget.Button; 
import android.widget.ListView; 

public class ListDataActivityInterv extends Activity{ 

    private ListView lsInterventiiView = null; 
    // private PacientiDB pacientiDB = null; 
    //private PacientiAdapter adapter = null; 
    // private ArrayList<Interventii> listInterventii = null; 
    Button button ; 
    String text = null; 
    ListView lv; 

    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.listviewinterventii); 
     lv = (ListView) findViewById(R.id.listView1);   


     //text = getIntent().getExtras().getString("Pacienti"); 
     //TextView textView1 = (TextView) findViewById(R.id.textView2); 
     // textView1.setText(text); 

     button = (Button) findViewById(R.id.button1); 
     button.setOnClickListener(new OnClickListener() { 

      @Override 
       public void onClick(View v) { 
        Intent intent = new Intent(ListDataActivityInterv.this, ListViewMultipleSelectionActivity.class); 
        startActivity(intent); 
        finish(); 
       } 
     }); 
     Bundle b = getIntent().getExtras(); 
      if(b!=null && b.containsKey("selectedItems")){ 

      String[] resultArr = b.getStringArray("selectedItems");  
      ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, resultArr);   
      lv.setAdapter(adapter); } 
        } 

} 

这是ListViewMultipleSelectionActivity。

package com.pranav.listviewdemo; 

import java.util.ArrayList; 

import android.app.Activity; 
import android.content.Intent; 
import android.os.Bundle; 
import android.util.SparseBooleanArray; 
import android.view.View; 
import android.view.View.OnClickListener; 
import android.widget.ArrayAdapter; 
import android.widget.Button; 
import android.widget.ListView; 
import android.widget.TextView; 


public class ListViewMultipleSelectionActivity extends Activity implements OnClickListener { 

    Button button; 
    ListView listView; 
    ArrayAdapter<String> adapter; 
    public String text = null; 
    //private PacientiDB pacientiDB = null; 

    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.maincheckinterv); 
     //text = getIntent().getExtras().getString("Pacienti"); 
     //TextView text1 = (TextView) findViewById(R.id.textViewListInter); 
     //text1.setText(text); 
     findViewsById(); 
     String[] sports = new String[]{"Cricket","football","game1","chess"}; 
     adapter = new ArrayAdapter<String>(this, 
       android.R.layout.simple_list_item_multiple_choice, sports); 
     listView.setChoiceMode(ListView.CHOICE_MODE_MULTIPLE); 
     listView.setAdapter(adapter); 
     button.setOnClickListener(this); 
    } 

    private void findViewsById() { 
     listView = (ListView) findViewById(R.id.listView2); 
     button = (Button) findViewById(R.id.button2); 
    } 

    public void onClick(View v) { 
     //Interventii interventie = pacientiDB.getInterv(text); 
     SparseBooleanArray checked = listView.getCheckedItemPositions(); 
     ArrayList<String> selectedItems = new ArrayList<String>(); 
     for (int i = 0; i < checked.size(); i++) { 

      int position = checked.keyAt(i); 

      if (checked.valueAt(i)) 
       selectedItems.add(adapter.getItem(position)); 
     } 
     String[] outputStrArr = new String[selectedItems.size()]; 
     for (int i = 0; i < selectedItems.size(); i++) { 
      outputStrArr[i] = selectedItems.get(i); 
     // interventie = new Interventii(); 
     // interventie.setDenumire(selectedItems.get(i)); 
     // pacientiDB.insertI(interventie); 
     } 
     Intent intent = new Intent(getApplicationContext(), 
       ListDataActivityInterv.class); 
     Bundle b = new Bundle(); 
     b.putStringArray("selectedItems", outputStrArr); 
     intent.putExtras(b); 
     startActivity(intent); 
    } 
} 

布局：-listviewinterventii.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical" > 

    <Button 
     android:id="@+id/button1" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Button" /> 

    <ListView 
     android:id="@+id/listView1" 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" > 
    </ListView> 

</LinearLayout> 

布局：-maincheckinterv.xml

<?xml version="1.0" encoding="utf-8"?> 
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:orientation="vertical" > 

    <Button 
     android:id="@+id/button2" 
     android:layout_width="wrap_content" 
     android:layout_height="wrap_content" 
     android:text="Button" /> 

    <ListView 
     android:id="@+id/listView2" 
     android:layout_width="match_parent" 
     android:layout_height="390dp" > 
    </ListView> 



</LinearLayout> 

清单

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.pranav.listviewdemo" 
    android:versionCode="1" 
    android:versionName="1.0" > 

    <uses-sdk 
     android:minSdkVersion="8" 
     android:targetSdkVersion="17" /> 

    <application 
     android:allowBackup="true" 
     android:icon="@drawable/ic_launcher" 
     android:label="@string/app_name" 
     android:theme="@style/AppTheme" > 
     <activity 
      android:name="com.pranav.listviewdemo.ListDataActivityInterv" 
      android:label="@string/app_name" 
      android:launchMode="singleInstance" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.LAUNCHER" /> 
      </intent-filter> 
     </activity> 
     <activity 
      android:name="com.pranav.listviewdemo.ListViewMultipleSelectionActivity" 
      android:label="@string/app_name" 
      android:launchMode="singleInstance" > 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

       <category android:name="android.intent.category.DEFAULT" /> 
      </intent-filter> 
     </activity> 
    </application> 

</manifest> 

Answer 2

行ListView listView;在你的第二个类中创建一个对listView的引用，但是，你没有实例化这个对象。在某些时候，您需要执行以下操作;

listView = new ListView(getApplicationContext()); 

或者从该上下文中可用的另一个列表视图中为其分配一个引用。

Answer 3

您的字符串数组为null

 Bundle b = getIntent().getExtras();   
     String[] resultArr = b.getStringArray("selectedItems"); 
     if(resultArr==null) 
     finish();  
     ListView lv = (ListView) findViewById(R.id.lsvListInterventii);   
     ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_list_item_1, resultArr);   
     lv.setAdapter(adapter); 

现在检查乌尔应用比，乌尔字符串数组为null直接关闭。??

您还可以检查该捆绑包是否有字符串数组.......如果它的数组是否为null或不是。

b.containsKey(resultArr)