Just learn a few days of android development, Java is not good QAQ
Now in the school's big homework problems solving

Error: under 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

Part of the code:

 private LinearLayoutManager LayoutManager. 
Private void initview () {
//get RecyclerView instance 
RecyclerView RecyclerView=the findViewById (R.i d.r ecycler); 

LayoutManager=new LinearLayoutManager (this); 
LayoutManager. SetOrientation (LinearLayoutManager. HORIZONTAL); 
RecyclerView. SetLayoutManager (LayoutManager); 
MyAdapter adapter=new MyAdapter (listpic, this); 
//complete adapter set 
RecyclerView. SetAdapter (adapter); 

} 

The complete code:

 
Package com. Xxca. Cherry. Fragments; 

The import android. Graphics. Drawable. Drawable; 
The import android. Support. The v4. App. Fragments; 
The import android. Support. The v4. App. FragmentManager; 
The import android. Support. The v4. App. FragmentTransaction; 
The import android. Support. V7. App. AppCompatActivity; 
The import android. OS. Bundle; 
The import android. Support. V7. Widget. LinearLayoutManager; 
The import android. Support. V7. Widget. OrientationHelper; 
The import android. Support. V7. Widget. RecyclerView; 
The import android. View. The view; 
The import android. Widget. TextView; 

The import com. Xxca. Cherry. R; 
The import com. Xxca. Cherry. Entity. PIC; 
The import com. Xxca. Cherry. RecycleView. MyAdapter; 

Import the Java. Util. ArrayList; 
Import the Java. Util. List; 

Public class firstActivity extends AppCompatActivity implements the View. An OnClickListener {
TextView tvmain, tvfind tvme; 
Fragments mainfragment, findfragment mefragment; 
FragmentManager FragmentManager; 
Private LinearLayoutManager LayoutManager. 
Private List Listpic=new ArrayList<> (a); 
Protected void onCreate (Bundle savedInstanceState) {
super.onCreate(savedInstanceState); 
The setContentView (R.l ayout. Activity_first); 
FragmentManager=getSupportFragmentManager ();//get manager 
Inittv ();//initialize 
Tvmain. PerformLongClick ();//simulate click 

//recyclerview 
The getid (); 
//set the RecyclerView 

Initview (); 
} 

Private void initview () {
//get RecyclerView instance 
RecyclerView RecyclerView=the findViewById (R.i d.r ecycler); 

LayoutManager=new LinearLayoutManager (this); 
LayoutManager. SetOrientation (LinearLayoutManager. HORIZONTAL); 
RecyclerView. SetLayoutManager (LayoutManager); 
MyAdapter adapter=new MyAdapter (listpic, this); 
//complete adapter set 
RecyclerView. SetAdapter (adapter); 

} 

Private void getid () {
PIC pic_1=new PIC (R.d rawable. Header_pic_ad1); 
PIC pic_2=new PIC (R.d rawable. Header_pic_ad2); 
Listpic. Add (pic_1); 
Listpic. Add (pic_2); 

} 


Private void inittv () {
Tvmain=the findViewById (R.i which vmain); 
Tvfind=the findViewById (R.i which vfind); 
Tvme=the findViewById (R.i which vme); 
Tvmain. SetOnClickListener (this); 
Tvfind. SetOnClickListener (this); 
Tvme. SetOnClickListener (this); 
} 

//hide 
Private void hideall (FragmentTransaction FragmentTransaction) 
{
If (mainfragment!=null) fragmentTransaction. Hide (mainfragment); 
If (findfragment!=null) fragmentTransaction. Hide (findfragment); 
If (mefragment!=null) fragmentTransaction. Hide (mefragment); 
} 

Private void setnormal () 
{
Drawable Drawable=getResources (). GetDrawable (R.d rawable. Nav_main_normal); 
//the top left corner starting position, the new size 
Drawable. SetBounds (0, 0, drawable getMinimumWidth (), drawable. GetMinimumHeight ()); 
//can be set in the icon, don't display set to null 
Tvmain. SetCompoundDrawables (null, drawable, null, null); 

Drawable drawable2=getResources (). GetDrawable (R.d rawable. Nav_find_normal); 
//the top left corner starting position, the new size 
Drawable2. SetBounds (0, 0, drawable2 getMinimumWidth (), drawable2. GetMinimumHeight ()); 
//can be set in the icon, don't display set to null 
Tvfind. SetCompoundDrawables (null, drawable2, null, null); 

//to get replacement picture 
Drawable drawable3=getResources (). GetDrawable (R.d rawable. Nav_me_normal); 
//the top left corner starting position, the new size 
Drawable3. SetBounds (0, 0, drawable3 getMinimumWidth (), drawable3. GetMinimumHeight ()); 
//can be set in the icon, don't display set to null 
Tvme. SetCompoundDrawables (null, drawable3, null, null); 

} 
@ Override 
Public void onClick (View View) {
FragmentTransaction FragmentTransaction=fragmentManager. BeginTransaction ();//open transaction 
//Toast. MakeText (firstActivity. This, "selected", Toast. LENGTH_LONG), show (); 
The switch (the getId ()) 
{
Case R.i which vmain: 
Setnormal (); 
//to get replacement picture 
Drawable Drawable=getResources (). GetDrawable (R.d rawable. Nav_main_click); 
//the top left corner starting position, the new size 
Drawable. SetBounds (0, 0, drawable getMinimumWidth (), drawable. GetMinimumHeight ()); 
//can be set in the icon, don't display set to null 
Tvmain. SetCompoundDrawables (null, drawable, null, null); 
Hideall (fragmentTransaction); 
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