在我的Android应用中，ViewPager，FragmentActivity创建了ViewPager。
在onCreate方法中，我尝试为OnClickListener设置Button。但在编译我的应用程序崩溃后。如果我删除所有setOnClickListener的所有内容。
你能帮助我吗？
public class MainActivity extends FragmentActivity {
AdvicePageAdapter pageAdapter;
Spinner categoriesSpinner;
Button blueButton, greenButton, pinkButton, greyButton, yellowButton;
private OnClickListener oclBtn;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
List<Fragment> fragments = getFragments();
pageAdapter = new AdvicePageAdapter(getSupportFragmentManager(), fragments);
ViewPager pager = (ViewPager)findViewById(R.id.viewpager);
pager.setAdapter(pageAdapter);
blueButton = (Button) findViewById(R.id.blueButton);
greenButton = (Button) findViewById(R.id.greenButton);
pinkButton = (Button) findViewById(R.id.pinkButton);
greyButton = (Button) findViewById(R.id.greyButton);
yellowButton = (Button) findViewById(R.id.yellowButton);
oclBtn = new OnClickListener (){
@Override
public void onClick(View v){
}
};
blueButton.setOnClickListener(oclBtn);
greenButton.setOnClickListener(oclBtn);
pinkButton.setOnClickListener(oclBtn);
greyButton.setOnClickListener(oclBtn);
yellowButton.setOnClickListener(oclBtn);
}
}
我的logcat
04-12 11:31:33.567: E/AndroidRuntime(2748): FATAL EXCEPTION: main
04-12 11:31:33.567: E/AndroidRuntime(2748): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.eugene.greatadvice/com.eugene.greatadvice.MainActivity}: java.lang.NullPointerException
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.app.ActivityThread.access$600(ActivityThread.java:141)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.os.Handler.dispatchMessage(Handler.java:99)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.os.Looper.loop(Looper.java:137)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.app.ActivityThread.main(ActivityThread.java:5103)
04-12 11:31:33.567: E/AndroidRuntime(2748): at java.lang.reflect.Method.invokeNative(Native Method)
04-12 11:31:33.567: E/AndroidRuntime(2748): at java.lang.reflect.Method.invoke(Method.java:525)
04-12 11:31:33.567: E/AndroidRuntime(2748): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
04-12 11:31:33.567: E/AndroidRuntime(2748): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
04-12 11:31:33.567: E/AndroidRuntime(2748): at dalvik.system.NativeStart.main(Native Method)
04-12 11:31:33.567: E/AndroidRuntime(2748): Caused by: java.lang.NullPointerException
04-12 11:31:33.567: E/AndroidRuntime(2748): at com.eugene.greatadvice.MainActivity.onCreate(MainActivity.java:83)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.app.Activity.performCreate(Activity.java:5133)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
04-12 11:31:33.567: E/AndroidRuntime(2748): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
04-12 11:31:33.567: E/AndroidRuntime(2748): ... 11 more
主要布局文件：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical" >
<TextView
android:id="@+id/textViewAdvice"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_centerHorizontal="true"
android:layout_centerVertical="true"
android:textAppearance="?android:attr/textAppearanceLarge" />
</RelativeLayout>
FragmentFile：
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:orientation="vertical"
android:background="@color/grey" >
<TextView
android:id="@+id/categoriesTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentTop="true"
android:layout_alignParentLeft="true"
android:layout_marginLeft = "15dip"
android:layout_marginTop = "15dip"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="@string/categoriesTitle"
android:textColor="@color/white"
android:textSize="17sp" />
<TextView
android:id="@+id/setingsTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentBottom="true"
android:layout_alignParentLeft="true"
android:layout_marginLeft = "15dip"
android:layout_marginBottom = "15dip"
android:textAppearance="?android:attr/textAppearanceLarge"
android:text="@string/settingsTitle"
android:textColor="@color/white"
android:textSize="35sp"/>
<Spinner
android:id="@+id/categorieSpinner"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_marginLeft = "15dip"
android:layout_marginRight = "15dip"
android:layout_marginTop = "15dip"
android:layout_below="@+id/categoriesTitle"
android:entries="@array/categories_array"
android:background="@color/white"
android:paddingTop="5dip"
android:paddingBottom="5dip"
android:textSize="17sp" />
<TextView
android:id="@+id/colorsTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/categorieSpinner"
android:layout_below="@+id/categorieSpinner"
android:layout_marginTop="20dp"
android:text="@string/colorsTitle"
android:textAppearance="?android:attr/textAppearanceLarge"
android:textColor="@color/white"
android:textSize="17sp" />
<View
android:id="@+id/colorsBG"
android:layout_width="84dip"
android:layout_height="84dip"
android:layout_below="@+id/colorsTitle"
android:layout_marginLeft = "13dip"
android:layout_marginTop = "13dip"
android:background="@color/white" />
<Button
android:id="@+id/blueButton"
android:layout_width="80dip"
android:layout_height="80dip"
android:layout_marginLeft = "15dip"
android:layout_marginTop = "15dip"
android:layout_below="@+id/colorsTitle"
android:background="@color/blue"
/>
<Button
android:id="@+id/greenButton"
android:layout_width="80dip"
android:layout_height="80dip"
android:layout_marginLeft = "110dip"
android:layout_marginTop = "15dip"
android:layout_below="@+id/colorsTitle"
android:background="@color/green"
/>
<Button
android:id="@+id/pinkButton"
android:layout_width="80dip"
android:layout_height="80dip"
android:layout_marginLeft = "205dip"
android:layout_marginTop = "15dip"
android:layout_below="@+id/colorsTitle"
android:background="@color/pink"
/>
<Button
android:id="@+id/greyButton"
android:layout_width="80dip"
android:layout_height="80dip"
android:layout_marginLeft = "15dip"
android:layout_marginTop = "110dip"
android:layout_below="@+id/colorsTitle"
android:background="@color/lightGrey"
/>
<Button
android:id="@+id/yellowButton"
android:layout_width="80dip"
android:layout_height="80dip"
android:layout_marginLeft = "110dip"
android:layout_marginTop = "110dip"
android:layout_below="@+id/colorsTitle"
android:background="@color/yellow"
/>
</RelativeLayout>
完整活动代码
package com.eugene.greatadvice;
import java.util.ArrayList;
import java.util.List;
import android.os.Bundle;
import android.support.v4.app.Fragment;
import android.support.v4.app.FragmentActivity;
import android.support.v4.app.FragmentManager;
import android.support.v4.app.FragmentPagerAdapter;
import android.support.v4.view.ViewPager;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.RelativeLayout.LayoutParams;
import android.widget.Spinner;
public class MainActivity extends FragmentActivity {
AdvicePageAdapter pageAdapter;
Spinner categoriesSpinner;
Button blueButton, greenButton, pinkButton, greyButton, yellowButton;
View colorsBG;
public OnClickListener oclBtn = new OnClickListener()
{
@Override
public void onClick(View v)
{
if(v == blueButton)
{
}
if(v == greenButton)
{
}
if(v == pinkButton)
{
}
if(v == greyButton)
{
}
if(v == yellowButton)
{
}
}
};
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
List<Fragment> fragments = getFragments();
pageAdapter = new AdvicePageAdapter(getSupportFragmentManager(), fragments);
ViewPager pager = (ViewPager)findViewById(R.id.viewpager);
pager.setAdapter(pageAdapter);
colorsBG = findViewById(R.id.colorsBG);
//init actions
categoriesSpinner = (Spinner) findViewById(R.id.categorieSpinner);
blueButton = (Button) findViewById(R.id.blueButton);
greenButton = (Button) findViewById(R.id.greenButton);
pinkButton = (Button) findViewById(R.id.pinkButton);
greyButton = (Button) findViewById(R.id.greyButton);
yellowButton = (Button) findViewById(R.id.yellowButton);
blueButton.setOnClickListener(oclBtn);
greenButton.setOnClickListener(oclBtn);
pinkButton.setOnClickListener(oclBtn);
greyButton.setOnClickListener(oclBtn);
yellowButton.setOnClickListener(oclBtn);
}
private List<Fragment> getFragments(){
List<Fragment> fList = new ArrayList<Fragment>();
fList.add(SettingsFragment.newInstance(""));
fList.add(AdviceFragment.newInstance(""));
return fList;
}
private class AdvicePageAdapter extends FragmentPagerAdapter {
private List<Fragment> fragments;
public AdvicePageAdapter(FragmentManager fm, List<Fragment> fragments) {
super(fm);
this.fragments = fragments;
}
@Override
public Fragment getItem(int position) {
return this.fragments.get(position);
}
@Override
public int getCount() {
return this.fragments.size();
}
}
}
答案 0 :(得分：2)
但是在编译我的应用程序后崩溃了。
NullPointerException正在发生，因为您在Fragment处于不合适状态时尝试访问onCreate()的视图。这些按钮是片段布局的一部分，该片段仅在onCreate()回调中实例化，其视图将在方法Activity之后创建，因此试图找到这些按钮不存在的片段视图将使引用为空。
您正在做的事情也是错误的，因为它不是处理这种互动的好方法。片段应该被设计为自包含的项目，可以在需要的地方插入，从Activity中搜索片段的视图中断并将片段绑定到/**
* An interface that will transmit the click events to the Activity
*/
public interface ClickDispatch {
void onClickReceived(View btn);
}
（不是提到错误的可能性很高）。为避免这种情况（以及上述问题），如果这是您想要的，请使用接口将点击事件从片段传输到活动：
public class MainActivity extends FragmentActivity implements ClickDispatch {
// code...
@Override
public void onClickReceived(View btn) {
// one of the fragment's buttons(btn) was clicked so do stuff
}
活动将实现此界面
onCreate()然后删除按钮的发现并在Activity的 ClickDispatch mListener;
// in the fragment class
@Override
public void onAttach(Activity activity) {
super.onAttach(activity);
// this is where the activity is passed to the fragment, we use this to cast the
// activity to our listener to pass it the click events
mListener = (ClickDispatch) activity;
}
// in the onCreateView method of the fragment:
View inflatedView = inflater.inflate(/*your layout*/);
blueButton = (Button) inflatedView.findViewById(R.id.blueButton);
greenButton = (Button) inflatedView.findViewById(R.id.greenButton);
pinkButton = (Button) inflatedView.findViewById(R.id.pinkButton);
greyButton = (Button) inflatedView.findViewById(R.id.greyButton);
yellowButton = (Button) inflatedView.findViewById(R.id.yellowButton);
OnClickListener oclBtn = new OnClickListener (){
@Override
public void onClick(View v){
// dispatch the click event to the Activity
if (mListener != null) {
mListener.onClickReceived(v);
}
}
};
blueButton.setOnClickListener(oclBtn);
greenButton.setOnClickListener(oclBtn);
pinkButton.setOnClickListener(oclBtn);
greyButton.setOnClickListener(oclBtn);
yellowButton.setOnClickListener(oclBtn);
方法中设置监听器，并在具有按钮的片段中执行：
{{1}}
答案 1 :(得分：1)
您的按钮和其他视图正在虚张声势，而不是您的活动，因此findViewById()正在为这些ID返回null。如果您想将Buttons等放在Activity中，请将这些元素从FragmentFile移动到activity_main.xml。否则，将View初始化和方法移动到Fragment类。