Why is assigning an OnClickListener to AutoCompleteTextView giving a NullPointerException?

问题

Whenever I assign an android:onClick attribute to an AutoCompleteTextView, my application immediately crashes upon loading the activity. I've tested AutoCompleteTextView without assigning an onClick method and it seems to work fine, as does assigning onClick to other views (including EditText, Spinners, TextViews, Buttons and ImageButtons). I've managed to narrow down the error to specifically to line 24 (setContentView(R.layout.activity_main)). Can anyone shed some light on this?

MainActivity.java

    package com.example.matt.testapp;

import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.AutoCompleteTextView;

public class MainActivity extends AppCompatActivity {
    public AutoCompleteTextView actv;
    public String[] continents = {"North America",
            "South America",
            "Antarctica",
            "Europe",
            "Africa",
            "Asia",
            "Australia"
    };


    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        actv = (AutoCompleteTextView) findViewById(R.id.actv);
        ArrayAdapter<String> adapter = new ArrayAdapter<>(this, android.R.layout.simple_list_item_1, continents);
        actv.setAdapter(adapter);
    }

    public void actvClick (View view) {}
}

activity_main.xml

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

    <AutoCompleteTextView
        android:id="@+id/actv"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:onClick="actvClick" >
    </AutoCompleteTextView>
</LinearLayout>

Logcat

java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.matt.testapp/com.example.matt.testapp.MainActivity}: android.view.InflateException: Binary XML file line #7: Binary XML file line #7: Error inflating class AutoCompleteTextView
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2817)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)
Caused by: android.view.InflateException: Binary XML file line #7: Binary XML file line #7: Error inflating class AutoCompleteTextView
Caused by: android.view.InflateException: Binary XML file line #7: Error inflating class AutoCompleteTextView
Caused by: java.lang.NullPointerException: Attempt to write to field 'android.view.View$OnClickListener android.widget.AutoCompleteTextView$PassThroughClickListener.mWrapped' on a null object reference
at android.widget.AutoCompleteTextView$PassThroughClickListener.-set0(Unknown Source:0)
at android.widget.AutoCompleteTextView.setOnClickListener(AutoCompleteTextView.java:307)
at android.view.View.<init>(View.java:5008)
at android.widget.TextView.<init>(TextView.java:824)
at android.widget.EditText.<init>(EditText.java:88)
at android.widget.AutoCompleteTextView.<init>(AutoCompleteTextView.java:220)
at android.widget.AutoCompleteTextView.<init>(AutoCompleteTextView.java:193)
at android.widget.AutoCompleteTextView.<init>(AutoCompleteTextView.java:172)
at android.support.v7.widget.AppCompatAutoCompleteTextView.<init>(AppCompatAutoCompleteTextView.java:68)
at android.support.v7.widget.AppCompatAutoCompleteTextView.<init>(AppCompatAutoCompleteTextView.java:64)
at android.support.v7.app.AppCompatViewInflater.createView(AppCompatViewInflater.java:130)
at android.support.v7.app.AppCompatDelegateImplV9.createView(AppCompatDelegateImplV9.java:1026)
at android.support.v7.app.AppCompatDelegateImplV9.onCreateView(AppCompatDelegateImplV9.java:1083)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:772)
at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:730)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:863)
at android.view.LayoutInflater.rInflateChildren(LayoutInflater.java:824)
at android.view.LayoutInflater.inflate(LayoutInflater.java:515)
at android.view.LayoutInflater.inflate(LayoutInflater.java:423)
at android.view.LayoutInflater.inflate(LayoutInflater.java:374)
at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:289)
at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:139)
at com.example.matt.testapp.MainActivity.onCreate(MainActivity.java:24)
at android.app.Activity.performCreate(Activity.java:6975)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1213)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2770)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2892)
at android.app.ActivityThread.-wrap11(Unknown Source:0)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1593)
at android.os.Handler.dispatchMessage(Handler.java:105)
at android.os.Looper.loop(Looper.java:164)
at android.app.ActivityThread.main(ActivityThread.java:6541)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.Zygote$MethodAndArgsCaller.run(Zygote.java:240)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:767)

回答1:

This looks like to be a bug in AutoCompleteTextView.

What happens:

Inflating the XML invokes AutoCompleteTextView constructor, and it invokes View constructor.
View constructor sees the onClick attribute and calls setOnClickListener().
AutoCompleteTextView has overridden setOnClickListener() which writes to an internal mPassThroughClickListener field. It is only initialized at the end of AutoCompleteTextView constructor, and this init code has not been run yet.

Reference

To work around it, remove the onClick attrtibute from your XML and call setOnClickListener() programmatically in your code.

I filed a bug about this in Android issue tracker.

来源：https://stackoverflow.com/questions/46363110/why-is-assigning-an-onclicklistener-to-autocompletetextview-giving-a-nullpointer

标签

android