我尝试使用CardView使用ToogleButton实现可扩展/折叠Animating Layout Changes，允许用户隐藏或显示CardView内的内容。当我尝试运行该应用时，Android Studio向我显示了以下消息：
FATAL EXCEPTION: main
Process: com.appmac.ron.expandcards, PID: 29977
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.appmac.ron.expandcards/com.appmac.ron.expandcards.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.ViewGroup.setVisibility(int)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2298)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
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:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.view.ViewGroup.setVisibility(int)' on a null object reference
at com.appmac.ron.expandcards.MainActivity.onCreate(MainActivity.java:36)
at android.app.Activity.performCreate(Activity.java:5933)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1105)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2251)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2360)
at android.app.ActivityThread.access$800(ActivityThread.java:144)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1278)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5221)
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:899)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:694)
MainActivity.java
package com.appmac.ron.expandcards;
import android.content.Context;
import android.os.Bundle;
import android.support.design.widget.FloatingActionButton;
import android.support.design.widget.Snackbar;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.Toolbar;
import android.view.LayoutInflater;
import android.view.View;
import android.view.Menu;
import android.view.MenuItem;
import android.view.ViewGroup;
import android.widget.RelativeLayout;
import android.widget.ToggleButton;
public class MainActivity extends AppCompatActivity {
private ViewGroup mContainerView;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
Toolbar toolbar = (Toolbar) findViewById(R.id.toolbar);
setSupportActionBar(toolbar);
FloatingActionButton fab = (FloatingActionButton) findViewById(R.id.fab);
fab.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
Snackbar.make(view, "Replace with your own action", Snackbar.LENGTH_LONG)
.setAction("Action", null).show();
}
});
mContainerView = (ViewGroup) findViewById(R.id.container);
mContainerView.setVisibility(View.INVISIBLE);
}
public void changeVisibility(View view){
boolean checked = ((ToggleButton)view).isChecked();
if(checked){
mContainerView.setVisibility(View.VISIBLE);
}
else{
mContainerView.setVisibility(View.INVISIBLE);
}
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.menu_main, menu);
return true;
}
@Override
public boolean onOptionsItemSelected(MenuItem item) {
// Handle action bar item clicks here. The action bar will
// automatically handle clicks on the Home/Up button, so long
// as you specify a parent activity in AndroidManifest.xml.
int id = item.getItemId();
//noinspection SimplifiableIfStatement
if (id == R.id.action_settings) {
return true;
}
return super.onOptionsItemSelected(item);
}
}
的AndroidManifest.xml
<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
package="com.appmac.ron.expandcards">
<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"
android:label="@string/app_name"
android:theme="@style/AppTheme.NoActionBar">
<intent-filter>
<action android:name="android.intent.action.MAIN" />
<category android:name="android.intent.category.LAUNCHER" />
</intent-filter>
</activity>
</application>
</manifest>
activity_main.xml中
<?xml version="1.0" encoding="utf-8"?>
<android.support.design.widget.CoordinatorLayout 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"
android:fitsSystemWindows="true"
tools:context="com.appmac.ron.expandcards.MainActivity">
<android.support.design.widget.AppBarLayout
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:theme="@style/AppTheme.AppBarOverlay">
<android.support.v7.widget.Toolbar
android:id="@+id/toolbar"
android:layout_width="match_parent"
android:layout_height="?attr/actionBarSize"
android:background="?attr/colorPrimary"
app:popupTheme="@style/AppTheme.PopupOverlay" />
</android.support.design.widget.AppBarLayout>
<include layout="@layout/content_main" />
<android.support.design.widget.FloatingActionButton
android:id="@+id/fab"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_gravity="bottom|end"
android:layout_margin="@dimen/fab_margin"
android:src="@android:drawable/ic_dialog_email" />
<RelativeLayout 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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
app:layout_behavior="@string/appbar_scrolling_view_behavior"
tools:context="com.appmac.ron.expandcards.MainActivity"
tools:showIn="@layout/activity_main">
<android.support.v7.widget.CardView xmlns:card_view="http://schemas.android.com/apk/res-auto"
android:id="@+id/cardFacebook"
android:layout_width="fill_parent"
android:layout_height="150dp"
android:layout_marginLeft="10dp"
android:layout_marginRight="10dp"
android:layout_marginTop="10dp"
android:background="?attr/selectableItemBackground"
android:clickable="true"
card_view:cardCornerRadius="0dp">
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="50dp"
android:id="@+id/relativeLayoutTop">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="TOP"
android:id="@+id/textViewTop" />
<ToggleButton
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textOff="Show More"
android:textOn="Hide"
android:id="@+id/toggleButton"
android:layout_centerVertical="true"
android:layout_alignParentRight="true"
android:layout_alignParentEnd="true"
android:backgroundTint="#fbfbfb"
android:textColor="#006199"
android:onClick="changeVisibility"/>
</RelativeLayout>
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="100dp"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="false"
android:layout_below="@+id/container"
android:layout_marginTop="50dp"
android:divider="?android:dividerHorizontal"
android:animateLayoutChanges="true">
<TextView
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="BOTTOM"
android:id="@+id/textViewBottom" />
</RelativeLayout>
</android.support.v7.widget.CardView>
</RelativeLayout>
<
/android.support.design.widget.CoordinatorLayout>
关于TranistionLayout： http://developer.android.com/intl/es/training/animation/layout.html
坦克提供任何帮助！
答案 0 :(得分：2)
除非我错过了它，看起来你没有在任何地方定义容器ID，只有引用似乎在你的相对布局的layout_below标签中。
编辑：我会发表评论但我还无法发表评论
如果您尝试引用RelativeLayout，那么
<RelativeLayout
android:layout_width="fill_parent"
android:layout_height="100dp"
android:layout_alignParentLeft="true"
android:layout_alignParentStart="false"
android:id="@+id/container"
android:layout_marginTop="50dp"
android:divider="?android:dividerHorizontal"
android:animateLayoutChanges="true">
应该修复它，否则包括
android:id="@+id/container
标记您要查找的内容