Question

R.id.icon已在Android API级别1中定义。但是，我在使用Android Design Support Library访问使用R.id.icon充气的imageview时，在targetSdk内部代码中获得了NPE。

注意：我不定位奥利奥，因为25目前是Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'android.view.ViewGroup$LayoutParams android.widget.ImageView.getLayoutParams()' on a null object reference at android.support.design.internal.BottomNavigationItemView.setChecked(BottomNavigationItemView.java:172) at android.support.design.internal.BottomNavigationItemView.initialize(BottomNavigationItemView.java:97) at android.support.design.internal.BottomNavigationMenuView.buildMenuView(BottomNavigationMenuView.java:276) at android.support.design.internal.BottomNavigationPresenter.updateMenuView(BottomNavigationPresenter.java:62) at android.support.design.widget.BottomNavigationView.inflateMenu(BottomNavigationView.java:238) at android.support.design.widget.BottomNavigationView.<init>(BottomNavigationView.java:167) at android.support.design.widget.BottomNavigationView.<init>(BottomNavigationView.java:116) at java.lang.reflect.Constructor.newInstance(Native Method) at java.lang.reflect.Constructor.newInstance(Constructor.java:288) at android.view.LayoutInflater.createView(LayoutInflater.java:607) at android.view.LayoutInflater.createViewFromTag(LayoutInflater.java:743) at android.view.LayoutInflater.rInflate(LayoutInflater.java:806) at android.view.LayoutInflater.inflate(LayoutInflater.java:504) at android.view.LayoutInflater.inflate(LayoutInflater.java:414) at android.view.LayoutInflater.inflate(LayoutInflater.java:365) at android.support.v7.app.AppCompatDelegateImplV9.setContentView(AppCompatDelegateImplV9.java:292) at android.support.v7.app.AppCompatActivity.setContentView(AppCompatActivity.java:140) at com.who.android.app.layout.activities.Sample_Mock.onCreate(Sample_Mock.java:40) at android.app.Activity.performCreate(Activity.java:6033) at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106) at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278) at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387) at android.app.ActivityThread.access$800(ActivityThread.java:151) at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303) at android.os.Handler.dispatchMessage(Handler.java:102) at android.os.Looper.loop(Looper.java:135) at android.app.ActivityThread.main(ActivityThread.java:5254) at java.lang.reflect.Method.invoke(Native Method) at java.lang.reflect.Method.invoke(Method.java:372) at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903) at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)。

这是stacktrace：

ImageView

经过调查，我发现BottomNavigationItemView.java中的代码正在尝试访问使用R.id.icon资源充实的空LayoutParams iconParams = (LayoutParams) mIcon.getLayoutParams();。

mIcon

其中null为mIcon = (ImageView) findViewById(R.id.icon);且已被夸大为

BottomNavigationActivity

编辑：我在Android的画廊中创建了一个新的package com.who.android.app.layout.activities; import android.os.Bundle; import android.support.annotation.NonNull; import android.support.design.widget.BottomNavigationView; import android.support.v7.app.AppCompatActivity; import android.view.MenuItem; import android.widget.TextView; import com.who.android.app.R; public class Sample_Mock extends AppCompatActivity { private TextView mTextMessage; private BottomNavigationView.OnNavigationItemSelectedListener mOnNavigationItemSelectedListener = new BottomNavigationView.OnNavigationItemSelectedListener() { @Override public boolean onNavigationItemSelected(@NonNull MenuItem item) { switch (item.getItemId()) { case R.id.navigation_home: mTextMessage.setText(R.string.title_home); return true; case R.id.navigation_dashboard: mTextMessage.setText(R.string.title_dashboard); return true; case R.id.navigation_notifications: mTextMessage.setText(R.string.title_notifications); return true; } return false; } }; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_sample__mock); mTextMessage = (TextView) findViewById(R.id.message); BottomNavigationView navigation = (BottomNavigationView) findViewById(R.id.navigation); navigation.setOnNavigationItemSelectedListener(mOnNavigationItemSelectedListener); } }，并将导航重定向到此模拟类，而不是我的。我仍然面临同样的问题。以下是原始java代码和新模拟活动的布局xml代码：

<?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:id="@+id/container"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical"
    tools:context="com._._._._.activities.Sample_Mock">

    <FrameLayout
        android:id="@+id/content"
        android:layout_width="match_parent"
        android:layout_height="0dp"
        android:layout_weight="1">

        <TextView
            android:id="@+id/message"
            android:layout_width="match_parent"
            android:layout_height="wrap_content"
            android:layout_marginBottom="@dimen/activity_vertical_margin"
            android:layout_marginLeft="@dimen/activity_horizontal_margin"
            android:layout_marginRight="@dimen/activity_horizontal_margin"
            android:layout_marginTop="@dimen/activity_vertical_margin"
            android:text="@string/title_home"/>

    </FrameLayout>

    <android.support.design.widget.BottomNavigationView
        android:id="@+id/navigation"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_gravity="bottom"
        android:background="?android:attr/windowBackground"
        app:menu="@menu/navigation"/>

</LinearLayout>

这是原始布局文件，我使用BottomNavigationView（由Android创建，我没有触及它）

com.android.support:design:25.3.1
com.android.support:appcompat-v7:25.3.1

我正在使用的Android设计支持库和Android AppCompat支持库的版本都是25.3.1

BottomNavigationActivity

任何人都可以帮助我理解为什么我从R.id.icon中获取一个空引用？此代码无法控制，因为它是Android设计支持库的内部代码。另外，正如我在新创建的Android Design Support中发现此问题一样，我使用的库版本是否存在问题？因为这个版本在过去的几个月里一直很好用。

编辑2：我创建了另一个项目，其中只有一个BottomNavigationActivity。你猜怎么着？同样的错误。所以在我看来，这是一个<?xml version="1.0" encoding="utf-8"?> <menu xmlns:android="http://schemas.android.com/apk/res/android"> <item android:id="@+id/navigation_home" android:icon="@drawable/ic_home_black_24dp" android:title="@string/title_home"/> <item android:id="@+id/navigation_dashboard" android:icon="@drawable/ic_dashboard_black_24dp" android:title="@string/title_dashboard"/> <item android:id="@+id/navigation_notifications" android:icon="@drawable/ic_notifications_black_24dp" android:title="@string/title_notifications"/> </menu>图书馆问题。

编辑3：menu / navigation.xml正如您所看到的，它是标准的。

"Launch &#128640;"

findViewById（R.id.icon）返回null

0 个答案: