Warum stört diese einfache Android-App nach der Verwendung von ListView?

Question

Ich schrieb eine Android-App, um das Konzept von ListView zu verstehen.

Die MainActivity.java Datei ist:

package com.example.swasik.firstday; 

import android.os.ParcelFileDescriptor; 
import android.support.v7.app.AppCompatActivity; 
import android.os.Bundle; 
import android.widget.ArrayAdapter; 
import android.widget.AutoCompleteTextView; 
import android.widget.ListAdapter; 
import android.widget.ListView; 

public class MainActivity extends AppCompatActivity { 

    String Age[] = {"11","222","33","44444","551"}; 
    String City[] = {"Pune","Delhi","Chennai","Kolkata"}; 


    @Override 
    protected void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 


     AutoCompleteTextView a = (AutoCompleteTextView) findViewById(R.id.autoCompleteTextView); 
     ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line,Age); 
     a.setAdapter(adapter); 

     ListView b = (ListView) findViewById(R.id.listView); 
     ArrayAdapter listAdapter = new ArrayAdapter<String>(this, android.R.layout.activity_list_item, City); 
     b.setAdapter(listAdapter); 

    } 
} 

Die activity_main.xml Datei ist:

<?xml version="1.0" encoding="utf-8"?> 
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android" 
    xmlns:tools="http://schemas.android.com/tools" 
    android:layout_width="match_parent" 
    android:layout_height="match_parent" 
    android:paddingBottom="@dimen/activity_vertical_margin" 
    android:paddingLeft="@dimen/activity_horizontal_margin" 
    android:paddingRight="@dimen/activity_horizontal_margin" 
    android:paddingTop="@dimen/activity_vertical_margin" 
    tools:context="com.example.swasik.firstday.MainActivity"> 

    <AutoCompleteTextView 
     android:layout_width="match_parent" 
     android:layout_height="wrap_content" 
     android:id="@+id/autoCompleteTextView" 
     android:completionThreshold="1" 
     /> 

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

    </ListView> 


</RelativeLayout> 

Die AndroidManifest.xml Datei ist:

<?xml version="1.0" encoding="utf-8"?> 
<manifest xmlns:android="http://schemas.android.com/apk/res/android" 
    package="com.example.swasik.firstday"> 

    <application 
     android:allowBackup="true" 
     android:icon="@mipmap/ic_launcher" 
     android:label="@string/app_name" 
     android:supportsRtl="true" 
     android:theme="@style/AppTheme"> 
     <activity android:name=".MainActivity"> 
      <intent-filter> 
       <action android:name="android.intent.action.MAIN" /> 

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

</manifest> 

im App läuft Auf Mobilgeräten wird folgende Meldung angezeigt: "Die App wurde leider gestoppt" Wie behebe ich dies?

Die logcat Datei zeigt:

04-17 22:50:21.794 1576-1576/com.example.swasik.firstday E/AndroidRuntime: FATAL EXCEPTION: main 
                      java.lang.IllegalStateException: ArrayAdapter requires the resource ID to be a TextView 
                       at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:386) 
                       at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362) 
                       at android.widget.AbsListView.obtainView(AbsListView.java:2465) 
                       at android.widget.ListView.measureHeightOfChildren(ListView.java:1250) 
                       at android.widget.ListView.onMeasure(ListView.java:1162) 
                       at android.view.View.measure(View.java:15598) 
                       at android.widget.RelativeLayout.measureChild(RelativeLayout.java:602) 
                       at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:415) 
                       at android.view.View.measure(View.java:15598) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118) 
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
                       at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135) 
                       at android.view.View.measure(View.java:15598) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118) 
                       at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:391) 
                       at android.view.View.measure(View.java:15598) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118) 
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
                       at android.view.View.measure(View.java:15598) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118) 
                       at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1396) 
                       at android.widget.LinearLayout.measureVertical(LinearLayout.java:681) 
                       at android.widget.LinearLayout.onMeasure(LinearLayout.java:574) 
                       at android.view.View.measure(View.java:15598) 
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118) 
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310) 
                       at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2423) 
                       at android.view.View.measure(View.java:15598) 
                       at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2006) 
                       at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1245) 
                       at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1420) 
                       at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1138) 
                       at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4645) 
                       at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725) 
                       at android.view.Choreographer.doCallbacks(Choreographer.java:555) 
                       at android.view.Choreographer.doFrame(Choreographer.java:525) 
                       at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711) 
                       at android.os.Handler.handleCallback(Handler.java:615) 
                       at android.os.Handler.dispatchMessage(Handler.java:92) 
                       at android.os.Looper.loop(Looper.java:174) 
                       at android.app.ActivityThread.main(ActivityThread.java:4952) 
                       at java.lang.reflect.Method.invokeNative(Native Method) 
                       at java.lang.reflect.Method.invoke(Method.java:511) 
                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027) 
                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794) 
                       at dalvik.system.NativeStart.main(Native Method) 
                      Caused by: java.lang.ClassCastException: android.widget.LinearLayout cannot be cast to android.widget.TextView 
                       at android.widget.ArrayAdapter.createViewFromResource(ArrayAdapter.java:379) 
                       at android.widget.ArrayAdapter.getView(ArrayAdapter.java:362)  
                       at android.widget.AbsListView.obtainView(AbsListView.java:2465)  
                       at android.widget.ListView.measureHeightOfChildren(ListView.java:1250)  
                       at android.widget.ListView.onMeasure(ListView.java:1162)  
                       at android.view.View.measure(View.java:15598)  
                       at android.widget.RelativeLayout.measureChild(RelativeLayout.java:602)  
                       at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:415)  
                       at android.view.View.measure(View.java:15598)  
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118)  
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)  
                       at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:135)  
                       at android.view.View.measure(View.java:15598)  
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118)  
                       at android.support.v7.widget.ActionBarOverlayLayout.onMeasure(ActionBarOverlayLayout.java:391)  
                       at android.view.View.measure(View.java:15598)  
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118)  
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)  
                       at android.view.View.measure(View.java:15598)  
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118)  
                       at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1396)  
                       at android.widget.LinearLayout.measureVertical(LinearLayout.java:681)  
                       at android.widget.LinearLayout.onMeasure(LinearLayout.java:574)  
                       at android.view.View.measure(View.java:15598)  
                       at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5118)  
                       at android.widget.FrameLayout.onMeasure(FrameLayout.java:310)  
                       at com.android.internal.policy.impl.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2423)  
                       at android.view.View.measure(View.java:15598)  
                       at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2006)  
                       at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1245)  
                       at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1420)  
                       at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1138)  
                       at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:4645)  
                       at android.view.Choreographer$CallbackRecord.run(Choreographer.java:725)  
                       at android.view.Choreographer.doCallbacks(Choreographer.java:555)  
                       at android.view.Choreographer.doFrame(Choreographer.java:525)  
                       at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:711)  
                       at android.os.Handler.handleCallback(Handler.java:615)  
                       at android.os.Handler.dispatchMessage(Handler.java:92)  
                       at android.os.Looper.loop(Looper.java:174)  
                       at android.app.ActivityThread.main(ActivityThread.java:4952)  
                       at java.lang.reflect.Method.invokeNative(Native Method)  
                       at java.lang.reflect.Method.invoke(Method.java:511)  
                       at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1027)  
                       at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:794)  
                       at dalvik.system.NativeStart.main(Native Method)  
04-17 22:50:30.614 1576-1576/com.example.swasik.firstday I/Process: Sending signal. PID: 1576 SIG: 9 

Answer 1

diese Verwendung wird Ihr Problem lösen:

ArrayAdapter listAdapter = new ArrayAdapter<String (this,android.R.layout.simple_list_item_1, City); 

Answer 2

Der ArrayAdapter <> Konstruktor Sie verwenden nicht eine Textview-vorausgesetzt, es braucht. Verwenden Sie stattdessen den folgenden Konstruktor.

ArrayAdapter<String> adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, android.R.id.text1, Age); 

Answer 3

ArrayAdapter erwartet, dass das Layout Ressource Sie eine Textview als Wurzelelement enthält, sonst funktioniert es nicht, wie die Daten in die Ansicht zu binden. Wenn Sie ein komplexeres Layout angeben möchten, verwenden Sie den Konstruktor, der sowohl eine Layout-Ressource und die ID eines Textview in diesem Layout nimmt:

ArrayAdapter<String> adapter = new ArrayAdapter<>(this, 
     R.layout.activity_list_item, R.id.some_textview, City); 

vorwärts bewegen, können Sie feststellen, dass Ihre Daten komplizierter wird und dass ArrayAdapter ist einfach nicht genug, um zu erreichen, was Sie wollen. An diesem Punkt sollten Sie eine eigene ListAdapter-Klasse schreiben. Ich würde Sie auf ein altes Video mit der Bezeichnung The World Of ListView verweisen, das die Grundlagen von LIstViews behandelt. (An einem gewissen Punkt sollten Sie RecyclerView anstelle von ListView verwenden).