Question

我想通过点击照片个人资料转移到其他活动，我不知道该怎么做。当我定义它时，它总是给我一个错误。我想使用string-array名称中的ID移至另一项活动，请参阅 list_tutor.xml 和 strings.xml 。

a = (ImageView)findViewById(R.id.list_tutor);

如果我写的代码没有错误，但应用程序崩溃并停止工作：

11-30 05:57:30.787 7171-7171/com.example.abdullahalhajri.smarttutor D/AndroidRuntime: Shutting down VM
11-30 05:57:30.790 7171-7171/com.example.abdullahalhajri.smarttutor E/AndroidRuntime: FATAL EXCEPTION: main
  Process: com.example.abdullahalhajri.smarttutor, PID: 7171
  java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.abdullahalhajri.smarttutor/com.example.abdullahalhajri.smarttutor.activities.SearchRating}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2778)
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856)
      at android.app.ActivityThread.-wrap11(Unknown Source:0)
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589)
      at android.os.Handler.dispatchMessage(Handler.java:106)
      at android.os.Looper.loop(Looper.java:164)
      at android.app.ActivityThread.main(ActivityThread.java:6494)
      at java.lang.reflect.Method.invoke(Native Method)
      at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)
   Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.ListView.setAdapter(android.widget.ListAdapter)' on a null object reference
      at com.example.abdullahalhajri.smarttutor.activities.SearchRating.onCreate(SearchRating.java:63)
      at android.app.Activity.performCreate(Activity.java:7000)
      at android.app.Activity.performCreate(Activity.java:6991)
      at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1214)
      at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2731)
      at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2856) 
      at android.app.ActivityThread.-wrap11(Unknown Source:0) 
      at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1589) 
      at android.os.Handler.dispatchMessage(Handler.java:106) 
      at android.os.Looper.loop(Looper.java:164) 
      at android.app.ActivityThread.main(ActivityThread.java:6494) 
      at java.lang.reflect.Method.invoke(Native Method) 
      at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438) 
      at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

如果我写那个

a = (ImageView)findViewById(R.id.khalid)

（khalid是profile_pics项目中的项目见strings.xml），它在khalid上给出了红色错误：

无法解析符号“khalid”

主要活动

public class SearchRating extends Activity implements OnItemClickListener {
    ImageView a;
    String[] member_names;
    TypedArray profile_pics;
    String[] statues;
    String[] contactType;

    List<RowItem> rowItems;
    ListView mylistview;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.list_tutor);
        Intent intent0 = getIntent();

         a = (ImageView)findViewById(R.id.profile_pic);;
        a.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view1) {
               Intent myIntent = new Intent(SearchRating.this, TutorProfile.class);
            startActivity(myIntent);
                                 }
                             });
        rowItems = new ArrayList<RowItem>();

        member_names = getResources().getStringArray(R.array.Member_names);

        profile_pics = getResources().obtainTypedArray(R.array.profile_pics);

        statues = getResources().getStringArray(R.array.statues);

        contactType = getResources().getStringArray(R.array.contactType);

        for (int i = 0; i < member_names.length; i++) {
            RowItem item = new RowItem(member_names[i],
                    profile_pics.getResourceId(i, -1), statues[i],
                    contactType[i]);
            rowItems.add(item);
        }

        mylistview = (ListView) findViewById(R.id.list);
        CustomAdapter adapter = new CustomAdapter(this, rowItems);
        mylistview.setAdapter(adapter);

        mylistview.setOnItemClickListener(this);

    }

    @Override
    public void onItemClick(AdapterView<?> parent, View view, int position,
                            long id) {

        String member_name = rowItems.get(position).getMember_name();
        Toast.makeText(getApplicationContext(), "" + member_name,
                Toast.LENGTH_SHORT).show();
    }

}

CustomAdapter

package com.example.abdullahalhajri.smarttutor.activities;

/**
 * Created by Khalid on 11/27/17.
 */


import android.app.Activity;
import android.content.Context;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.BaseAdapter;
import android.widget.ImageView;
import android.widget.TextView;
import com.example.abdullahalhajri.smarttutor.R;
import java.util.List;

public class CustomAdapter extends BaseAdapter {

    Context context;
    List<RowItem> rowItems;

    CustomAdapter(Context context, List<RowItem> rowItems) {
        this.context = context;
        this.rowItems = rowItems;
    }

    @Override
    public int getCount() {
        return rowItems.size();
    }

    @Override
    public Object getItem(int position) {
        return rowItems.get(position);
    }

    @Override
    public long getItemId(int position) {
        return rowItems.indexOf(getItem(position));
    }

    /* private view holder class */
    private class ViewHolder {
        ImageView profile_pic;
        TextView member_name;
        TextView status;
        TextView contactType;
    }

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

        ViewHolder holder = null;

        LayoutInflater mInflater = (LayoutInflater) context
                .getSystemService(Activity.LAYOUT_INFLATER_SERVICE);
        if (convertView == null) {
            convertView = mInflater.inflate(R.layout.list_tutor, null);
            holder = new ViewHolder();

            holder.member_name = (TextView) convertView
                    .findViewById(R.id.member_name);
            holder.profile_pic = (ImageView) convertView
                    .findViewById(R.id.profile_pic);
            holder.status = (TextView) convertView.findViewById(R.id.status);
            holder.contactType = (TextView) convertView
                    .findViewById(R.id.contact_type);

            RowItem row_pos = rowItems.get(position);

            holder.profile_pic.setImageResource(row_pos.getProfile_pic_id());
            holder.member_name.setText(row_pos.getMember_name());
            holder.status.setText(row_pos.getStatus());
            holder.contactType.setText(row_pos.getContactType());

            convertView.setTag(holder);
        } else {
            holder = (ViewHolder) convertView.getTag();
        }

        return convertView;
    }

}

TutorProfile

package com.example.abdullahalhajri.smarttutor.activities;
import android.content.Intent;
import android.os.Bundle;
import android.support.v7.app.ActionBarActivity;

import com.example.abdullahalhajri.smarttutor.R;

public class TutorProfile extends ActionBarActivity {

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_tutorprofile);
        Intent intent0 = getIntent();
    }
}

list_tutor.xml

        <?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:padding="2dp" >

    <ImageView
        android:id="@+id/profile_pic"
        android:layout_width="70dp"
        android:layout_height="70dp"
        android:contentDescription="desc"
        android:paddingLeft="10dp"
        android:paddingRight="10dp" />

    <TextView
        android:id="@+id/member_name"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:layout_toRightOf="@+id/profile_pic"
        android:paddingBottom="10dp"
        android:text="txt"
        android:textSize="20sp" />

    <TextView
        android:id="@+id/status"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignLeft="@+id/member_name"
        android:layout_below="@+id/member_name"
        android:text="txt"
        android:textSize="16sp" />

    <TextView
        android:id="@+id/contact_type"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBaseline="@+id/member_name"
        android:layout_alignBottom="@+id/member_name"
        android:layout_alignParentRight="true"
        android:text="txt"
        android:textSize="16sp" />

</RelativeLayout>

的strings.xml

  <!-- ListviewTuruor -->
    <string name="action_settings">Settings</string>
    <string name="hello_world">Hello world!</string>
    <!-- Names -->
    <string-array name="Member_names">

        <item>Robert</item>
        <item>Shanni</item>
        <item>Rachael</item>
        <item>Maddy</item>
        <item>Kate</item>
        <item>Emma</item>
        <item>Isabella</item>
        <item>Khalid</item>
        <item>Sophia</item>
    </string-array>

    <!-- Pictures -->
    <array name="profile_pics">
        <item>@drawable/robert</item>
        <item>@drawable/shanni</item>
        <item>@drawable/rachael</item>
        <item>@drawable/maddy_pic</item>
        <item>@drawable/kate</item>
        <item>@drawable/nikhil_pic</item>
        <item>@drawable/isabella</item>
        <item>@drawable/khalid</item>
        <item>@drawable/sophia</item>
    </array>

    <!-- Status -->
    <string-array name="statues">
        <item>Math</item>
        <item>IT</item>
        <item>Biology</item>
        <item>English</item>
        <item>Art</item>
        <item>Natural Science</item>
        <item>Art</item>
        <item>Networking</item>
        <item>Chemistry</item>
    </string-array>

    <!-- contact type -->
    <string-array name="contactType">
        <item>4.7/5</item>
        <item>4.6/5</item>
        <item>4.4/5</item>
        <item>4/5</item>
        <item>3.9/5</item>
        <item>3.5/5</item>
        <item>3.5/5</item>
        <item>2.7/5</item>
        <item>2/5</item>
    </string-array>

布局 activity_search_rating

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

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

Answer 1

例外情况告诉您，在SearchRating.java文件中，您正在访问尚未初始化的ListView。

查看您的list_tutor.xml文件，该ID没有ListView，这就是SearchRating的{{1}}中抛出NullPointerException的原因。

您要为onCreate

添加ID为ListView的{{1}}

修改的

获取drawable：使用此方法（将其添加到您的活动中）

list

然后在名为list_tutor.xml

的方法中添加以下内容

public Drawable getDrawableByStringId(String strId) {
    int id = getResources().getIdentifier(strId, "drawable", getPackageName());
    return getDrawable(id);
}

您设置项目的方式不必要地复杂化。所以我回答了你项目的设置。

希望你能学到更多并意识到这一点。

Answer 2

首先，您无法定义a = (ImageView)findViewById(R.id.khalid);您需要定义它a = (ImageView)findViewById(R.id.list_tutor);

然后根据您的日志，它显示您传递给适配器的值为null。由于这个原因，你的应用程序正在崩溃。尝试使用断点调试应用程序，以检查setAdapter

时传递的值

 mylistview = (ListView) findViewById(R.id.list);
        CustomAdapter adapter = new CustomAdapter(this, rowItems); // Here might be problem.
        mylistview.setAdapter(adapter);

第三件事是定义你的

a.setOnClickListener(new View.OnClickListener() {
            public void onClick(View view1) {
               Intent myIntent = new Intent(SearchRating.this, TutorProfile.class);
            startActivity(myIntent);
                                 }
                             });

在customAdapter中

，

单击ImageView移动到另一个活动

2 个答案: