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首页 > 解决方案 > 当按下 menuItem 以在 android 中显示用于列表视图的自定义适配器时，应用程序崩溃

android - 当按下 menuItem 以在 android 中显示用于列表视图的自定义适配器时，应用程序崩溃

问题描述

每当按下 menuItem 时，我都会尝试显示一个列表视图。我想显示自定义布局，因为我需要用于无法正常工作且我的应用程序崩溃的列表视图的自定义适配器。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......前一个也停止工作了，我不知道为什么！我也在许多论坛上看到了几乎所有与此相关的问题，但对我没有任何帮助。请帮助我哪里错了..

下面是我的菜单项代码..

  @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“debach”的菜单项时，我开始新的活动，我打算在其中显示自定义列表视图，我收到错误和应用程序崩溃..

该部分的代码如下...

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 DisplayDebcha 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>

我收到以下错误..

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.

非常感谢任何帮助:)

标签： androidandroid-studioandroid-listviewandroid-arrayadaptercustom-adapter

解决方案

我的错...这只是一个愚蠢的错误，视图构造函数中的错字使 Dnumber 为空:(

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

我正在初始化 2 次 Dname。

经验教训：请检查您的错字:)

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