为什么将OnClickListener分配给AutoCompleteTextView会给出NullPointerException?

问题描述

每当我将android:onClick属性分配给AutoCompleteTextView时，加载活动时我的应用程序立即崩溃.我已经测试了AutoCompleteTextView而不分配onClick方法，它似乎可以正常工作，就像将onClick分配给其他视图(包括EditText，Spinners，TextViews，Button和ImageButtons)一样.我设法将错误缩小到第24行(setContentView(R.layout.activity_main)).谁能对此有所启发?

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)

推荐答案

这似乎是AutoCompleteTextView中的错误.

会发生什么:

1. 膨胀XML会调用AutoCompleteTextView构造函数，并且会调用View构造函数.
2. View构造函数看到onClick属性并调用setOnClickListener().
3. AutoCompleteTextView已被覆盖的setOnClickListener()覆盖了内部的mPassThroughClickListener字段.它仅在AutoCompleteTextView构造函数的末尾进行初始化，并且此初始化代码尚未运行.

1. Inflating the XML invokes AutoCompleteTextView constructor, and it invokes View constructor.
2. View constructor sees the onClick attribute and calls setOnClickListener().
3. 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.

参考

要解决此问题，请从XML中删除onClick属性，并以编程方式在代码中调用setOnClickListener().

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

我在Android问题跟踪器中对此提交了错误.

I filed a bug about this in Android issue tracker.

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