錯誤描述：
E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.sxau.qy.justright, PID: 5943
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.sxau.qy.justright/com.sxau.qy.justright.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2913)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.support.v7.widget.RecyclerView.setLayoutManager(android.support.v7.widget.RecyclerView$LayoutManager)' on a null object reference
at com.sxau.qy.justright.MainActivity.onCreate(MainActivity.java:67)
at android.app.Activity.performCreate(Activity.java:7136)
at android.app.Activity.performCreate(Activity.java:7127)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1271)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2893)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:3048)
at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:78)
at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1808)
at android.os.Handler.dispatchMessage(Handler.java:106)
at android.os.Looper.loop(Looper.java:193)
at android.app.ActivityThread.main(ActivityThread.java:6669)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
I/Process: Sending signal. PID: 5943 SIG: 9
Application terminated.
uj5u.com熱心網友回復：
public class MainActivity extends BaseActivity implements View.OnClickListener{//將每一個文字和圖示所在的線性布局控制元件生成（為了實作點擊監聽）。
private LinearLayout TextAndIcon_ID_justright;
private LinearLayout TextAndIcon_ID_findout;
private LinearLayout TextAndIcon_ID_news;
private LinearLayout TextAndIcon_ID_fresh;
private LinearLayout TextAndIcon_ID_self;
//將每一個圖示按鈕生成（為了換圖示）。
private ImageButton IconChange_ID_justright;
private ImageButton IconChange_ID_findout;
private ImageButton IconChange_ID_news;
private ImageButton IconChange_ID_fresh;
private ImageButton IconChange_ID_self;
//將每一個碎片布局實體化。
//將每一個碎片布局生成。
private Fragment justright_fragment;
private Fragment findout_fragment;
private Fragment news_fragment;
private Fragment fresh_fragment;
private Fragment self_fragment;
private List<JR_Pages_CardsMode> cardsList=new ArrayList<>();//new
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
requestWindowFeature(Window.FEATURE_NO_TITLE);//去掉頭頂bar
setContentView(R.layout.activity_main);//加載布局檔案
// initView();//之前所有的物體都沒有初始化，該函式是為了初始化所有
// selectTab(0);//選擇要進行顯示替換的布局，通過傳參決定
//!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!new
initCards();
RecyclerView recyclerView=findViewById(R.id.ListView);
// LinearLayoutManager layoutManager = new LinearLayoutManager(this);
LinearLayoutManager layoutManager = new LinearLayoutManager(this);
recyclerView.setLayoutManager(layoutManager);
// layoutManager.setOrientation(OrientationHelper.VERTICAL);
CardsAdapter adapter= new CardsAdapter(cardsList);
recyclerView.setAdapter(adapter);
initView();//之前所有的物體都沒有初始化，該函式是為了初始化所有
selectTab(0);//選擇要進行顯示替換的布局，通過傳參決定
}
//new
private void initCards(){
for (int i=0;i<2;i++){
JR_Pages_CardsMode one=new JR_Pages_CardsMode(R.drawable.image_userall,"user","Test");
cardsList.add(one);
JR_Pages_CardsMode two=new JR_Pages_CardsMode(R.drawable.image_userall,"user","Test");
cardsList.add(two);
JR_Pages_CardsMode three=new JR_Pages_CardsMode(R.drawable.image_userall,"user","Test");
cardsList.add(three);
// JR_Pages_CardsMode four=new JR_Pages_CardsMode(R.drawable.image_userall,"user","Test");
// cardsList.add(four);
// JR_Pages_CardsMode five=new JR_Pages_CardsMode(R.drawable.image_userall,"user","Test");
// cardsList.add(five);
}
}
//該函式是為了初始化所有
private void initView() {
//將每一個文字和圖示所在的線性布局控制元件生成（為了實作點擊監聽）
TextAndIcon_ID_justright=findViewById(R.id.linearlayout_bottomNO1_justRight);
TextAndIcon_ID_findout=findViewById(R.id.linearlayout_bottomNO2_findOut);
TextAndIcon_ID_news=findViewById(R.id.linearlayout_bottomNO3_news);
TextAndIcon_ID_fresh=findViewById(R.id.linearlayout_bottomNO4_fresh);
TextAndIcon_ID_self=findViewById(R.id.linearlayout_bottomNO5_self);
//實作點擊監聽
TextAndIcon_ID_justright.setOnClickListener(this);
TextAndIcon_ID_findout.setOnClickListener(this);
TextAndIcon_ID_news.setOnClickListener(this);
TextAndIcon_ID_fresh.setOnClickListener(this);
TextAndIcon_ID_self.setOnClickListener(this);
//將每一個圖示按鈕和布局檔案關聯
IconChange_ID_justright=findViewById(R.id.imagebutton_buttonNO1_justRight);
IconChange_ID_findout=findViewById(R.id.imagebutton_buttonNO2_findOut);
IconChange_ID_news=findViewById(R.id.imagebutton_buttonNO3_news);
IconChange_ID_fresh=findViewById(R.id.imagebutton_buttonNO4_fresh);
IconChange_ID_self=findViewById(R.id.imagebutton_buttonNO5_self);
justright_fragment=new NO1_JustRight_Fragment();
findout_fragment=new NO2_FindOut_Fragment();
news_fragment=new NO3_News_Fragment();
fresh_fragment=new NO4_Fresh_Fragment();
self_fragment=new NO5_Self_Fragment();
}
private void selectTab(int i) {
FragmentManager fm=getFragmentManager();
FragmentTransaction transaction=fm.beginTransaction();//生成可切換背景的操作物件
switch (i){
case 0:
// NO1_JustRight_Fragment justright_fragment=new NO1_JustRight_Fragment();
IconChange_ID_justright.setImageResource(R.drawable.justright_pressed);
transaction.replace(R.id.content_useForChange,justright_fragment);
break;
case 1:
// NO2_FindOut_Fragment findout_fragment=new NO2_FindOut_Fragment();
IconChange_ID_findout.setImageResource(R.drawable.findout_pressed);
transaction.replace(R.id.content_useForChange,findout_fragment);
break;
case 2:
// NO3_News_Fragment news_fragment=new NO3_News_Fragment();
IconChange_ID_news.setImageResource(R.drawable.news_pressed);
transaction.replace(R.id.content_useForChange,news_fragment);
break;
case 3:
// NO4_Fresh_Fragment fresh_fragment=new NO4_Fresh_Fragment();
IconChange_ID_fresh.setImageResource(R.drawable.fresh_pressed);
transaction.replace(R.id.content_useForChange,fresh_fragment);
break;
case 4:
// NO5_Self_Fragment self_fragment=new NO5_Self_Fragment();
IconChange_ID_self.setImageResource(R.drawable.self_pressed);
transaction.replace(R.id.content_useForChange,self_fragment);
break;
default:
break;
}
transaction.commit();
}
//將對于每個底部控制顯示的文字和圖示所在的線性布局控制元件的監聽進行了邏輯書寫
@Override
public void onClick(View arg0) {
resetImage();//自己寫的方法——為了在每一次點擊的一瞬間先進行所有圖示初始化，之后再進行選擇
switch (arg0.getId()){
case R.id.linearlayout_bottomNO1_justRight:
selectTab(0);
break;
case R.id.linearlayout_bottomNO2_findOut:
selectTab(1);
break;
case R.id.linearlayout_bottomNO3_news:
selectTab(2);
break;
case R.id.linearlayout_bottomNO4_fresh:
selectTab(3);
break;
case R.id.linearlayout_bottomNO5_self:
selectTab(4);
break;
default: break;
}
}
//先將圖示初始化
private void resetImage() {
IconChange_ID_justright.setImageResource(R.drawable.justright_nomal);
IconChange_ID_findout.setImageResource(R.drawable.findout_nomal);
IconChange_ID_news.setImageResource(R.drawable.news_nomal);
IconChange_ID_fresh.setImageResource(R.drawable.fresh_nomal);
IconChange_ID_self.setImageResource(R.drawable.self_nomal);
}
}
uj5u.com熱心網友回復：
public class CardsAdapter extends RecyclerView.Adapter<CardsAdapter.ViewHolder> {private List<JR_Pages_CardsMode> nowCardsThing;
static class ViewHolder extends RecyclerView.ViewHolder {
ImageButton userPhotoImage;
TextView userNickName;
TextView userContent;
//--------待定---------
public ViewHolder(@NonNull View view) {
super(view);
userPhotoImage=(ImageButton) view.findViewById(R.id.imagebutton_justrightPages_TouXiang);
userNickName=(TextView)view.findViewById(R.id.textview_justrightPages_UserName);
userContent=(TextView)view.findViewById(R.id.textview_justrightPages_Content);
}
}
public CardsAdapter(List<JR_Pages_CardsMode> CardsThing){
nowCardsThing=CardsThing;
}
@NonNull
@Override
public ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {
View view= LayoutInflater.from(parent.getContext()).inflate(R.layout.justrightpages_listview,parent,false);
final ViewHolder holder=new ViewHolder(view);
return holder;
}
@Override
public void onBindViewHolder(@NonNull ViewHolder holder, int position) {
JR_Pages_CardsMode cards=nowCardsThing.get(position);
holder.userPhotoImage.setImageResource(cards.getImageId());
holder.userNickName.setText(cards.getNickname());
holder.userContent.setText(cards.getContent());
}
@Override
public int getItemCount() {
return nowCardsThing.size();
}
}
uj5u.com熱心網友回復：
只看錯誤日志已經很明顯了，你的RecyclerView是空的，多半是你這個布局里沒有ListView這個id，你再檢查檢查。另外學會看錯誤日志是很重要的基礎技能哦uj5u.com熱心網友回復：
哥，我那個id是有的，按住ctrl可以跳過去，名字一模一樣??三天了真的不會解決uj5u.com熱心網友回復：
我覺得你還是在確定一下這個 ListView的id是在你的activity_main.xml里嗎？如果是在activity下的fragment里是找不到的。很明顯的錯誤uj5u.com熱心網友回復：
能跳過去只是代表有這個id，但不代表你的id在你當前activtiy的布局里
uj5u.com熱心網友回復：
1.之前遇到過同名或者名字非常像的兩個activity，除錯的時候斷點也不進去。2.雖然能跳過去，個人感覺不一定代表就在你的activity里面，找不到應該就是沒有，不用懷疑。
3.你可以在跳過去的那個布局里面再加一個布局，肯定還是找不到的。
uj5u.com熱心網友回復：
空指標例外，遇到問題，看日志，很清楚了告訴你了。學會找問題，然后分析問題。uj5u.com熱心網友回復：
我的main_activity里面是個fragment然后有好幾個頁面，點擊不用的按鈕，在main_activity切換布局，我那個list view在（姑且叫做page1）page1布局里面寫的uj5u.com熱心網友回復：
所以你需要在page1布局對應的fragment里使用這個RecyclerView，而不是在MainActivity中
uj5u.com熱心網友回復：
哥，我就在對應的頁面寫的recycleview，但是沒有涉及到切換activityuj5u.com熱心網友回復：
uj5u.com熱心網友回復：
對不起啊哥，我太菜了，沒咋聽懂??……現在似懂非懂我再看看，謝謝你uj5u.com熱心網友回復：
沒咋聽懂??……現在似懂非懂我再看看uj5u.com熱心網友回復：
哥！我弄出來了??臥槽，大哥牛逼，真的太謝謝了，一語點破了我，非常感謝，真的很謝謝，謝謝！轉載請註明出處，本文鏈接：https://www.uj5u.com/yidong/108482.html
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