[按下menuItem在android中显示列表视图的自定义适配器时，应用程序崩溃

问题描述 投票：0回答：1

我试图在按下menuItem时显示一个列表视图。我想显示自定义布局，为此，我需要用于列表视图的自定义适配器，该适配器无法正常工作，并且我的应用崩溃了。我的android应用程序中有3-4个自定义适配器，它们工作正常，但是自从我添加了另一个适配器后，...上一个也停止了工作，我不知道为什么！在许多论坛上，我几乎也看到了与此相关的每个问题，但对我来说却无济于事。请在我错的地方帮助我。.

下面是我的menuItems代码。

  @Override
    public boolean onOptionsItemSelected(MenuItem menuItem){
        switch (menuItem.getItemId()){
            case R.id.settings:
                Intent intent = new Intent(this, OpenSettings.class);
                startActivity(intent);
                break;
            case R.id.debacha:
                Intent intent1 = new Intent(AyahsDisplay.this,DebachaDisplay.class);
                this.startActivity(intent1);
                break;
        }
        return super.onOptionsItemSelected(menuItem);
    }

当按下ID为“ debacha”的菜单项时，我正在启动新的活动，在该活动中，我将显示自定义列表视图，该错误和应用程序崩溃。

该部分的代码在下面...

public class DebachaDisplay extends AppCompatActivity {

    ListView list1;
    ArrayList<debacha> debachas = new ArrayList<>();
    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_debacha_display);

        try {
            parseXML(); //here i am parsing XML file to load data in "debachas" which is working fine
        } catch (XmlPullParserException e) { }
        catch (IOException e) { }

    }

private void printDebacha(ArrayList<debacha> debachas){
    list1 = findViewById(R.id.debachaList);
    CustomDebachaview customDebachaview = new CustomDebachaview(DebachaDisplay.this,debachas);
    list1.setAdapter(customDebachaview);
}

下面是DisplayDebacha活动的布局文件
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res-auto"
    xmlns:tools="http://schemas.android.com/tools"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    tools:context=".DebachaDisplay">

    <ListView
        android:id="@+id/debachaList"
        android:background="#FDFFE9"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        >
    </ListView>

</LinearLayout>

下面是我的自定义适配器类的代码...
package com.example.demo;

import android.app.Activity;
import android.content.Intent;
import android.util.TypedValue;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.TextView;
import android.widget.Toast;

import androidx.annotation.NonNull;
import androidx.annotation.Nullable;

import java.util.ArrayList;

public class CustomDebachaview extends ArrayAdapter<debacha> {
    private ArrayList<debacha> debachas;
    private Activity context;
    public CustomDebachaview(Activity context,ArrayList<debacha> debachas){
        super(context,R.layout.debacha_list_view,debachas);
        this.debachas = debachas;
        this.context = context;
    }
    @NonNull
    @Override
    public View getView(final int position , @Nullable View convertView , @Nullable final ViewGroup parent){
        View r = convertView;
        CustomDebachaview.viewHolder viewHolder = null;
        if(r == null){
            LayoutInflater layoutInflater = context.getLayoutInflater();
            r = layoutInflater.inflate(R.layout.debacha_list_view,null,true);
            viewHolder = new CustomDebachaview.viewHolder(r);
            r.setTag(viewHolder);
        }
        else {
            viewHolder = (CustomDebachaview.viewHolder) r.getTag();
        }

        viewHolder.Dnumber.setText("﴾ " + debachas.get(position).getDNumber() + " ﴿");
        viewHolder.Dname.setText(debachas.get(position).getDName());

        return r;
    }

    class viewHolder{
        TextView Dnumber;
        TextView Dname;
        viewHolder(View v){
            Dname = v.findViewById(R.id.Dnumber);
            Dname = v.findViewById(R.id.Dname);
        }
    }
}

下面是自定义适配器列表视图布局文件代码...
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <TextView
        android:id="@+id/Dnumber"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="debacha number"
        android:paddingLeft="5dp"
        android:textSize="17dp"
        android:textColor="#297B16"
        android:textStyle="bold"
        />
    <TextView
        android:id="@+id/Dname"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:text="Dname"
        android:textSize="25dp"
        android:textColor="#226A12"

        />

</LinearLayout>

我遇到以下错误。。
E/AndroidRuntime: FATAL EXCEPTION: main
    Process: com.example.demo, PID: 1040
    java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
        at com.example.demo.CustomDebachaview.getView(CustomDebachaview.java:42)
        at android.widget.AbsListView.obtainView(AbsListView.java:3219)
        at android.widget.ListView.makeAndAddView(ListView.java:2219)
        at android.widget.ListView.fillDown(ListView.java:827)
        at android.widget.ListView.fillFromTop(ListView.java:888)
        at android.widget.ListView.layoutChildren(ListView.java:1958)
        at android.widget.AbsListView.onLayout(AbsListView.java:2991)
        at android.view.View.layout(View.java:22407)
        at android.view.ViewGroup.layout(ViewGroup.java:6589)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutHorizontal(LinearLayout.java:1801)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1567)
        at android.view.View.layout(View.java:22407)
        at android.view.ViewGroup.layout(ViewGroup.java:6589)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:22407)
        at android.view.ViewGroup.layout(ViewGroup.java:6589)
        at androidx.appcompat.widget.ActionBarOverlayLayout.onLayout(ActionBarOverlayLayout.java:444)
        at android.view.View.layout(View.java:22407)
        at android.view.ViewGroup.layout(ViewGroup.java:6589)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at android.view.View.layout(View.java:22407)
        at android.view.ViewGroup.layout(ViewGroup.java:6589)
        at android.widget.LinearLayout.setChildFrame(LinearLayout.java:1812)
        at android.widget.LinearLayout.layoutVertical(LinearLayout.java:1656)
        at android.widget.LinearLayout.onLayout(LinearLayout.java:1565)
        at android.view.View.layout(View.java:22407)
        at android.view.ViewGroup.layout(ViewGroup.java:6589)
        at android.widget.FrameLayout.layoutChildren(FrameLayout.java:323)
        at android.widget.FrameLayout.onLayout(FrameLayout.java:261)
        at com.android.internal.policy.DecorView.onLayout(DecorView.java:1075)
        at android.view.View.layout(View.java:22407)
        at android.view.ViewGroup.layout(ViewGroup.java:6589)
        at android.view.ViewRootImpl.performLayout(ViewRootImpl.java:3371)
        at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:2840)
        at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1888)
        at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:8503)
        at android.view.Choreographer$CallbackRecord.run(Choreographer.java:949)
        at android.view.Choreographer.doCallbacks(Choreographer.java:761)
        at android.view.Choreographer.doFrame(Choreographer.java:696)
        at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:935)
        at android.os.Handler.handleCallback(Handler.java:873)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:214)
        at android.app.ActivityThread.main(ActivityThread.java:7073)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:964)
I/Process: Sending signal. PID: 1040 SIG: 9
Process 1040 terminated.

非常感谢您的帮助：）

我试图在按下menuItem时显示一个列表视图。我想显示自定义布局，为此，我需要用于列表视图的自定义适配器，该适配器无法正常工作，并且我的应用崩溃了。我...

android android-studio android-listview android-arrayadapter custom-adapter
1个回答
0
投票

我的糟糕……那是一个愚蠢的错误，viewholder构造函数中的一个错字使Dnumber为null：（

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