空指针在列表视图中实现OnClickListener的异常错误

Question

我试图实现一个列表视图，该列表视图通过调用和电子邮件选项显示一些联系人的列表。如果通话按钮被按下，那么它应该打电话给那个人，并与电子邮件按钮相同。

但问题在于： - 我在列表Activity中编写了OnClickListener，当它运行时，它给了我一个空指针异常的错误。

请指导。谢谢您的提前。

以下是我的代码。

MyActivity.java

package com.vanjasrivastava.customlistview; 

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

import android.app.Activity; 
import android.content.Intent; 
import android.net.Uri; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.ImageButton; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.SimpleAdapter; 
import android.widget.Toast; 

public class MyActivity extends Activity { 

    // Array of strings storing country names 
    String[] countries = new String[] {"Mr.Vikas Raina", "Mrs. Jeetu Sharma", "Mr.Kuashik Ghosh", "Mr.Niranjan Lal", "Ms. Swati Garg", "Ms. Manju", "Mr. M. Kakhani", }; 

    // Array of integers points to images stored in /res/drawable-ldpi/ 
    int[] flags = new int[]{R.drawable.vikas, R.drawable.jeetu, R.drawable.ghosh, R.drawable.nlal, R.drawable.swati, R.drawable.manju, R.drawable.manish}; 

    // Array of strings to store currencies 
    String[] currency = new String[]{"Assistant Professor", "Assistant Professor", "Assistant Professor", "Assistant Professor", "Assistant Professor", "Assistant Professor", "Assistant Professor",  }; 

    /** Called when the activity is first created. */ 
    @Override 
    public void onCreate(Bundle savedInstanceState) { 

    super.onCreate(savedInstanceState); 
    setContentView(R.layout.activity_my); 

    // Each row in the list stores country name, currency and flag 
    List<HashMap<String,String>> aList = new ArrayList<HashMap<String,String>>(); 

    for(int i=0;i<7;i++){ 

    HashMap<String, String> hm = new HashMap<String,String>(); 
    hm.put("txt", " " + countries[i]); 
    hm.put("cur"," " + currency[i]); 
    hm.put("flag", Integer.toString(flags[i])); 
      aList.add(hm); 
    } 

    // Keys used in Hashmap 
    String[] from = { "flag","txt","cur" }; 

    // Ids of views in listview_layout 
    int[] to = { R.id.flag,R.id.txt,R.id.cur}; 


    SpecialAdapter adapter = new SpecialAdapter(getBaseContext(), aList, R.layout.mylist, from, to); 
    // Getting a reference to listview of main.xml layout file 
    ListView listView = (ListView) findViewById(R.id.listview); 

    // Setting the adapter to the listView 
    listView.setAdapter(adapter); 

    ImageButton callButton = (ImageButton)findViewById(R.id.call); 
    ImageButton mailButton = (ImageButton)findViewById(R.id.email); 
    callButton.setOnClickListener(new View.OnClickListener() { 

    @Override 
    public void onClick(View v) { 

    if(v.getId()==R.id.email) { 

     phoneCall(); 
     } 
    } 
    }); 

    mailButton.setOnClickListener(new View.OnClickListener() { 

    @Override 
    public void onClick(View v) { 

    if(v.getId()==R.id.email) { 

      sendEmail(); 
     } 
     } 
     }); 
    } 

    private void phoneCall() { 

     String phoneCallUri ="tel:+91 1573 225001"; 
     Intent phoneCallIntent = new Intent(Intent.ACTION_CALL); 
     phoneCallIntent.setData(Uri.parse(phoneCallUri)); 
     startActivity(phoneCallIntent); 
    } 

    protected void sendEmail() { 

     Log.i("Send email", ""); 

     String[] TO = {"abc@gmail.com"}; 
     String[] CC = {"xyz@gmail.com"}; 
     Intent emailIntent = new Intent(Intent.ACTION_SEND); 
     emailIntent.setData(Uri.parse("mailto:")); 
     emailIntent.setType("text/plain"); 

     emailIntent.putExtra(Intent.EXTRA_EMAIL, TO); 
     emailIntent.putExtra(Intent.EXTRA_CC, CC); 
     emailIntent.putExtra(Intent.EXTRA_SUBJECT, "Your subject"); 
     emailIntent.putExtra(Intent.EXTRA_TEXT, "Email message goes here"); 

     try { 

      startActivity(Intent.createChooser(emailIntent, "Send mail...")); 
      finish(); 
      Log.i("Finished sending email...", ""); 
     } catch (android.content.ActivityNotFoundException ex) { 

      Toast.makeText(MyActivity.this, "There is no email client installed.", Toast.LENGTH_SHORT).show(); 
     } 
    } 
} 

SpecialAdapter.java

package com.vanjasrivastava.customlistview; 

/** 
* Created by vanjasrivastava on 11/21/14. 
*/ 
import java.util.HashMap; 
import java.util.List; 

import android.content.Context; 
import android.view.View; 
import android.view.ViewGroup; 
import android.widget.SimpleAdapter; 

public class SpecialAdapter extends SimpleAdapter { 

    private int[] colors = new int[] { 0x50888888, 0x7500aced }; 

    public SpecialAdapter(Context context, List<HashMap<String, String>> items, int resource, String[] from, int[] to) { 

     super(context, items, resource, from, to); 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 

     View view = super.getView(position, convertView, parent); 
     int colorPos = position % colors.length; 
     view.setBackgroundColor(colors[colorPos]); 
     return view; 
    } 
} 

mylist.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="horizontal" > 

    <ImageView 
     android:id="@+id/flag" 
     android:layout_width="110dp" 
     android:layout_height="130dp" 
     android:paddingTop="10dp" 
     android:paddingRight="10dp" 
     android:paddingBottom="10dp" /> 

    <LinearLayout 
     android:layout_width="match_parent" 
     android:layout_height="match_parent" 
     android:orientation="vertical" > 

     <TextView 
      android:id="@+id/txt" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_gravity="center_horizontal" 
      android:textSize="20dp" 
      android:paddingTop="30dp" 
      android:paddingRight="10dp" 
      android:paddingBottom="10dp" /> 

     <TextView 
      android:id="@+id/cur" 
      android:layout_width="wrap_content" 
      android:layout_height="wrap_content" 
      android:layout_gravity="center_horizontal" 
      android:textSize="15dp" 
      android:paddingTop="0.5dp" 
      android:paddingRight="5dp" 
      android:paddingBottom="5dp" /> 

     <LinearLayout 
      android:layout_width="fill_parent" 
      android:layout_height="fill_parent" 
      android:weightSum="1" 
      android:layout_gravity="center_horizontal"> 

      <ImageButton 
       android:id="@+id/call" 
       android:layout_width="40dp" 
       android:layout_height="40dp" 
       android:layout_weight="0.5" 
       android:paddingTop="10dp" 
       android:src="@drawable/cl" /> 

      <ImageButton 
       android:id="@+id/email" 
       android:layout_width="wrap_content" 
       android:layout_height="wrap_content" 
       android:layout_weight="0.5" 
       android:paddingTop="10dp" 
       android:paddingLeft="10dp" 
       android:src="@drawable/email" /> 

     </LinearLayout> 
    </LinearLayout> 
</LinearLayout> 

更新：

我做了一些变化，我的代码，但仍显示错误： at line 1. startActivity（Intent） - 错误是“无法解析方法” 2. finish（） - 错误是：“无法解析方法” 3. Toast.makeset（） - 错误是：“can not解决方法”

这里是我更新的代码：

MyActivity.java

package com.vanjasrivastava.customlistview; 
import java.util.ArrayList; 
import java.util.HashMap; 
import java.util.List; 
import android.app.Activity; 
import android.content.Intent; 
import android.net.Uri; 
import android.os.Bundle; 
import android.util.Log; 
import android.view.View; 
import android.widget.ImageButton; 
import android.widget.ImageView; 
import android.widget.ListView; 
import android.widget.SimpleAdapter; 
import android.widget.Toast; 

public class MyActivity extends Activity { 

// Array of strings storing country names 
String[] countries = new String[] { "Mr.Vikas Raina","Mrs. Jeetu Sharma","Mr.Kuashik Ghosh","Mr.Niranjan Lal","Ms. Swati Garg","Ms. Manju", "Mr. M. Kakhani",}; 
// Array of integers points to images stored in /res/drawable-ldpi/ 
int[] flags = new int[]{R.drawable.vikas,R.drawable.jeetu,R.drawable.ghosh,R.drawable.nlal,  R.drawable.swati,R.drawable.manju,R.drawable.manish}; 
// Array of strings to store currencies 
String[] currency = new String[]{"Assistant Professor","Assistant Professor","Assistant Professor",  "Assistant Professor","Assistant Professor","Assistant Professor","Assistant Professor"}; 

/** Called when the activity is first created. */ 
@Override 
public void onCreate(Bundle savedInstanceState) { 
super.onCreate(savedInstanceState); 
setContentView(R.layout.activity_my); 
// Each row in the list stores country name, currency and flag 
List<HashMap<String,String>> aList = new ArrayList<HashMap<String,String>>(); 
    for(int i=0;i<7;i++){ 
     HashMap<String, String> hm = new HashMap<String,String>(); 
     hm.put("txt", " " + countries[i]); 
     hm.put("cur"," " + currency[i]); 
     hm.put("flag", Integer.toString(flags[i])); 
     aList.add(hm); 
    } 

    // Keys used in Hashmap 
    String[] from = { "flag","txt","cur" }; 

    // Ids of views in listview_layout 
    int[] to = { R.id.flag,R.id.txt,R.id.cur}; 

    // Instantiating an adapter to store each items 
    // R.layout.listview_layout defines the layout of each item 
    //SimpleAdapter adapter = new SimpleAdapter(getBaseContext(), aList, R.layout.mylist, from, to); 
    SpecialAdapter adapter = new SpecialAdapter(getBaseContext(), aList, R.layout.mylist, from, to); 
    // Getting a reference to listview of main.xml layout file 
    ListView listView = (ListView) findViewById(R.id.listview); 

    // Setting the adapter to the listView 
    listView.setAdapter(adapter); 


    } 

} 

SpecialAdapter.java

package com.vanjasrivastava.customlistview; 

/** 
* Created by vanjasrivastava on 11/21/14. 
*/ 
    import java.util.HashMap; 
    import java.util.List; 
    import android.view.View; 
    import android.app.Activity; 
    import android.content.Context; 
    import android.content.Intent; 
    import android.net.Uri; 
    import android.util.Log; 
    import android.view.View; 
    import android.view.ViewGroup; 
    import android.widget.ImageButton; 
    import android.widget.SimpleAdapter; 
    import android.widget.Toast; 

    public class SpecialAdapter extends SimpleAdapter { 
    private int[] colors = new int[] { 0x50888888, 0x7500aced }; 
    ImageButton callButton; 
    ImageButton mailButton; 
    public SpecialAdapter(Context context, List<HashMap<String, String>> items, int resource, String[] from, int[] to) { 
    super(context, items, resource, from, to); 
    } 

    @Override 
    public View getView(int position, View convertView, ViewGroup parent) { 
    View view = super.getView(position, convertView, parent); 
    int colorPos = position % colors.length; 
    view.setBackgroundColor(colors[colorPos]); 


    callButton = (ImageButton) view.findViewById(R.id.call); 
    mailButton = (ImageButton) view.findViewById(R.id.email); 
    callButton.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 
     if (v.getId() == R.id.call) { 

       phoneCall(); 
      } 
     } 
    }); 
    mailButton.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 
     if (v.getId() == R.id.email) { 
       sendEmail(); 
      } 
     } 
    }); 
    return view; 
    } 
    private void phoneCall() 
    { 
     String phoneCallUri ="tel:+91 1573 225001"; 
     Intent phoneCallIntent = new Intent(Intent.ACTION_CALL); 
     phoneCallIntent.setData(Uri.parse(phoneCallUri)); 
     startActivity(phoneCallIntent); 
    } 
protected void sendEmail() { 
     Log.i("Send email", ""); 

     String[] TO = {"abc@gmail.com"}; 
     String[] CC = {"xyz@gmail.com"}; 
     Intent emailIntent = new Intent(Intent.ACTION_SEND); 
     emailIntent.setData(Uri.parse("mailto:")); 
     emailIntent.setType("text/plain"); 


     emailIntent.putExtra(Intent.EXTRA_EMAIL, TO); 
     emailIntent.putExtra(Intent.EXTRA_CC, CC); 
     emailIntent.putExtra(Intent.EXTRA_SUBJECT, "Your subject"); 
     emailIntent.putExtra(Intent.EXTRA_TEXT, "Email message goes here"); 

     try { 
      startActivity(Intent.createChooser(emailIntent, "Send mail...")); 
      finish(); 
      Log.i("Finished sending email...", ""); 
     } catch (android.content.ActivityNotFoundException ex) { 
      Toast.makeText(MyActivity.this, 
          "There is no email client installed.", Toast.LENGTH_SHORT).show(); 
     } 
    } 


} 

我该如何解决这些错误。 请指导。

Answer 1

的下面几行代码：

callButton.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 


     if(v.getId()==R.id.email) 
     { 

      phoneCall(); 

     } 
    } 
}); 

mailButton.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 
     if(v.getId()==R.id.email) 
     { 

      sendEmail(); 

     } 
    } 
}); 

移动上面的代码的SpecialAdapter的getView()方法。另外，将android:descendantFocusability="blocksDescendants"添加到mylist.xml的最顶端LinearLayout。这将工作。

Answer 2

在别的之前，你的代码无法按预期工作，因为当你按下通话按钮时，按钮ID是否为'email'，yeilds始终为false。你可以摆脱这些检查，他们是redundent。

也像别人所说的那样，您的onClick方法挂钩应该在您的自定义适配器的getView()方法中完成。

Answer 3

编写代码如下：

您SpecialAdapter.java应该像现在这样，从MyActivity.java

public class SpecialAdapter extends SimpleAdapter { 
    private int[] colors = new int[] { 0x50888888, 0x7500aced }; 
    ImageButton callButton ,mailButton; 


    public SpecialAdapter(Context context, List<HashMap<String, String>> items, int 
       resource, String[] from, int[] to) { 
      super(context, items, resource, from, to); 

     } 

@Override 
public View getView(int position, View convertView, ViewGroup parent) { 
    View view = super.getView(position, convertView, parent); 
    int colorPos = position % colors.length; 
    view.setBackgroundColor(colors[colorPos]); 

    callButton = (ImageButton)view .findViewById(R.id.call); 
    mailButton = (ImageButton)view .findViewById(R.id.email); 

    callButton.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 


     // Here you get the position of clicked item that you can retrive the value from 
     // array with the help of position 

      // phoneCall(); 


    } 
}); 

    mailButton.setOnClickListener(new View.OnClickListener() { 
    @Override 
    public void onClick(View v) { 

     // Here you get the position of clicked item that you can retrive the value from 
     // array with the help of position 

      // sendEmail(); 


    } 
    }); 

    return view; 
    } 
}