java.lang.NullPointerException：尝试在空对象引用上调用虚拟方法'Rec
我正在尝试实现一个recyclerview持有人以动态添加和删除卡。但是，为什么在尝试将cardview动态添加到recyclerview时却得到null指针异常？
MAINACTIVITY.JAVA此类负责动态创建卡片视图并将卡片添加到recyclerview。
package net.simplifiedlearning.recyclerviewexample;
import android.app.Dialog;
import android.content.Context;
import android.content.SharedPreferences;
import android.graphics.Color;
import android.graphics.Typeface;
import android.support.constraint.ConstraintLayout;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.support.v7.widget.CardView;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.support.v7.widget.SimpleItemAnimator;
import android.util.TypedValue;
import android.view.View;
import android.webkit.WebView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import java.util.ArrayList;
import java.util.List;
import android.view.LayoutInflater;
import android.widget.TextView;
import android.widget.Toast;
import android.widget.ToggleButton;
import android.widget.Toolbar;
public class MainActivity extends AppCompatActivity {
public Button buttonScan1;
private Button dev_but1;
public WebView wv1;
private Dialog add_dev;
private View v1;
private EditText text2;
private EditText dev_id1;
private EditText dev_name1;
private TextView dev_text1;
private CardView cardview2;
private LinearLayout.LayoutParams layoutparams1;
private ConstraintLayout.LayoutParams layoutparams2;
private LinearLayout lay1;
private LinearLayout lay2;
private LinearLayout lay3;
private ToggleButton sw1;
private ToggleButton sw2;
private ToggleButton sw3;
private ToggleButton sw4;
private LinearLayout ahomeLayout;
private Toolbar toolbar;
private LinearLayout lay4;
private LinearLayout lay6;
private LinearLayout lay5;
private LinearLayout.LayoutParams layoutparams3;
private Button sw0;
public TextView atv;
String ids[] = new String[100];
String names[] = new String[100];
String name_key[] = {"A","B","C","D","F","G","H","I","J"};
String id_key[] = {"A","B","C","D","F","G","H","I","J"};
public SharedPreferences mSettings2;
int mCount,j;
String name;
private Context mCtx;
//a list to store all the products
List<Product> productList;
RelativeLayout l1;
//the recyclerview
RecyclerView recyclerView;
Button end;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
//View view = getLayoutInflater().inflate(R.layout.layout_products,null);
end = findViewById(R.id.button2);
//getting the recyclerview from xml
recyclerView = findViewById(R.id.recyclerView);
recyclerView.setHasFixedSize(true);
recyclerView.setLayoutManager(new LinearLayoutManager(this));
//((SimpleItemAnimator) recyclerView.getItemAnimator()).setSupportsChangeAnimations(false);
end.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
cards();
}
});
//initializing the productlist
productList = new ArrayList<>();
//adding some items to our list
//productList.add(new Product(1,"sdc","sfs"));
//creating recyclerview adapter
ProductAdapter adapter = new ProductAdapter(this, productList);
//setting adapter to recyclerview
recyclerView.setAdapter(adapter);
}
public void cards()
{
/*text2 = v1.findViewById(R.id.dev_name);
dev_id1 = v1.findViewById(R.id.dev_id);*/
cardview2 = new CardView(getApplicationContext());
cardview2.setFocusable(false);
cardview2.setClickable(false);
layoutparams1 = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.WRAP_CONTENT);
layoutparams1.setMargins(19, 83, 19, 0);
lay1 = new LinearLayout(getApplicationContext());
lay1.setOrientation(LinearLayout.VERTICAL);
layoutparams2 = new ConstraintLayout.LayoutParams(ConstraintLayout.LayoutParams.MATCH_PARENT, 115);
lay2 = new LinearLayout(getApplicationContext());
lay2.setLayoutParams(layoutparams2);
lay2.setOrientation(LinearLayout.HORIZONTAL);
layoutparams3 = new LinearLayout.LayoutParams(LinearLayout.LayoutParams.MATCH_PARENT, LinearLayout.LayoutParams.MATCH_PARENT);
lay6 = new LinearLayout(getApplicationContext());
lay6.setWeightSum(12);
lay6.setLayoutParams(layoutparams3);
lay6.setPadding(10,40,0,0);
lay6.setOrientation(LinearLayout.HORIZONTAL);
cardview2.setLayoutParams(layoutparams1);
cardview2.setCardBackgroundColor(Color.parseColor("#2fffffff"));
cardview2.setMinimumHeight(330);
cardview2.setId(mCount);
cardview2.addView(lay1);
dev_text1 = new TextView(getApplicationContext());
dev_text1.setText("sdfasdf");
dev_text1.setPadding(20, 15,0,0);
dev_text1.setTextSize(TypedValue.COMPLEX_UNIT_DIP, 26);
dev_text1.setTypeface(null, Typeface.BOLD);
dev_text1.setTextColor(Color.GRAY);
sw1 = new ToggleButton(getApplicationContext());
sw1.setTextSize(TypedValue.COMPLEX_UNIT_DIP, 20);
sw1.setTextColor(Color.GRAY);
sw1.setLayoutParams(new LinearLayout.LayoutParams(210, 145));
sw2 = new ToggleButton(getApplicationContext());
sw2.setTextSize(TypedValue.COMPLEX_UNIT_DIP, 20);
sw2.setTextColor(Color.GRAY);
sw2.setLayoutParams(new LinearLayout.LayoutParams(210, 145));
sw3 = new ToggleButton(getApplicationContext());
sw3.setTextSize(TypedValue.COMPLEX_UNIT_DIP, 20);
sw3.setTextColor(Color.GRAY);
sw3.setLayoutParams(new LinearLayout.LayoutParams(210, 145));
sw4 = new ToggleButton(getApplicationContext());
sw4.setTextSize(TypedValue.COMPLEX_UNIT_DIP, 20);
sw4.setTextColor(Color.GRAY);
sw4.setLayoutParams(new LinearLayout.LayoutParams(210, 145));
sw0 = new Button(getApplicationContext());
sw0.setText(" X");
sw0.setTextSize(20);
sw0.setTypeface(null, Typeface.BOLD);
sw0.setBackgroundResource(0);
sw0.setTextColor(Color.GRAY);
sw0.setPadding(0,0,0,5);
sw0.setLayoutParams(new LinearLayout.LayoutParams(70, 70));
lay1.addView(lay2);
lay1.addView(lay6);
lay2.addView(dev_text1);
lay2.addView(sw0);
lay6.addView(sw1);
lay6.addView(sw2);
lay6.addView(sw3);
lay6.addView(sw4);
recyclerView.addView(cardview2);
}
}
产品.JAVA
package net.simplifiedlearning.recyclerviewexample;
public class Product {
private int id;
private String title;
private String shortdesc;
public Product(int id, String title, String shortdesc) {
this.id = id;
this.title = title;
this.shortdesc = shortdesc;
}
public int getId() {
return id;
}
public String getTitle() {
return title;
}
public String getShortdesc() {
return shortdesc;
}
}
PRODUCTADAPTER.JAVA此类在recyclerview中具有适配器。
package net.simplifiedlearning.recyclerviewexample;
import android.app.Dialog;
import android.content.Context;
import android.support.v7.widget.RecyclerView;
import android.util.TypedValue;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.webkit.WebView;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ImageView;
import android.widget.LinearLayout;
import android.widget.RelativeLayout;
import android.widget.TextView;
import android.widget.ToggleButton;
import android.widget.Toolbar;
import java.util.List;
public class ProductAdapter extends RecyclerView.Adapter<ProductAdapter.ProductViewHolder> {
//this context we will use to inflate the layout
private Context mCtx;
RelativeLayout l1;
//we are storing all the products in a list
private List<Product> productList;
//getting the context and product list with constructor
public ProductAdapter(Context mCtx, List<Product> productList) {
this.mCtx = mCtx;
this.productList = productList;
}
@Override
public ProductViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
//inflating and returning our view holder
LayoutInflater inflater = LayoutInflater.from(mCtx);
View view = inflater.inflate(R.layout.layout_products, null);
return new ProductViewHolder(view);
}
@Override
public void onBindViewHolder(final ProductViewHolder holder, int position) {
//getting the product of the specified position
Product product = productList.get(position);
//binding the data with the viewholder views
holder.textViewTitle.setText(product.getTitle());
holder.textViewShortDesc.setText(product.getShortdesc());
holder.end.setOnClickListener(new View.OnClickListener() {
@Override
public void onClick(View view) {
productList.remove(holder.getAdapterPosition());
notifyDataSetChanged();
}
});
}
@Override
public int getItemCount() {
return productList.size();
}
class ProductViewHolder extends RecyclerView.ViewHolder {
TextView textViewTitle, textViewShortDesc;
Button end;
public ProductViewHolder(View itemView) {
super(itemView);
l1 = itemView.findViewById(R.id.card);
textViewTitle = itemView.findViewById(R.id.textViewTitle);
textViewShortDesc = itemView.findViewById(R.id.textViewShortDesc);
end = itemView.findViewById(R.id.button);
}
}
}
布局_产品.Java
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:orientation="vertical">
<android.support.v7.widget.CardView
android:id="@+id/card1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_margin="5dp">
<RelativeLayout
android:id="@+id/card"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:padding="8dp">
<ImageView
android:id="@+id/imageView"
android:layout_width="120dp"
android:layout_height="90dp"
android:padding="4dp" />
<TextView
android:id="@+id/textViewTitle"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginLeft="5dp"
android:layout_toRightOf="@id/imageView"
android:text="Apple MacBook Air Core i5 5th Gen - (8 GB/128 GB SSD/Mac OS Sierra)"
android:textAppearance="@style/Base.TextAppearance.AppCompat.Small"
android:textColor="#000000" />
<TextView
android:id="@+id/textViewShortDesc"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/textViewTitle"
android:layout_marginLeft="5dp"
android:layout_marginTop="5dp"
android:layout_toRightOf="@id/imageView"
android:text="13.3 Inch, 256 GB"
android:textAppearance="@style/Base.TextAppearance.AppCompat.Small" />
<TextView
android:id="@+id/textViewRating"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/textViewShortDesc"
android:layout_marginLeft="5dp"
android:layout_marginTop="5dp"
android:layout_toRightOf="@id/imageView"
android:background="@color/colorPrimary"
android:paddingLeft="15dp"
android:paddingRight="15dp"
android:text="4.7"
android:textAppearance="@style/Base.TextAppearance.AppCompat.Small.Inverse"
android:textStyle="bold" />
<TextView
android:id="@+id/textViewPrice"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/textViewRating"
android:layout_marginLeft="5dp"
android:layout_marginTop="5dp"
android:layout_toRightOf="@id/imageView"
android:text="INR 56990"
android:textAppearance="@style/Base.TextAppearance.AppCompat.Large"
android:textStyle="bold" />
<Button
android:id="@+id/button"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Button" />
</RelativeLayout>
</android.support.v7.widget.CardView>
</LinearLayout>
activity_main.xml
<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
tools:context="net.simplifiedlearning.recyclerviewexample.MainActivity">
<android.support.v7.widget.RecyclerView
android:id="@+id/recyclerView"
android:layout_width="match_parent"
android:layout_height="match_parent" />
<Button
android:id="@+id/button2"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_marginTop="500dp"
android:text="ADD" />
</RelativeLayout>
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像这样更改onCreateViewHolder。
@Override public ProductViewHolder onCreateViewHolder(ViewGroup parent, int viewType) { //inflating and returning our view holder LayoutInflater inflater = LayoutInflater.from(mCtx); View view = inflater.inflate(R.layout.layout_products,parent, false); return new ProductViewHolder(view); }2020-01-19 11:40:53赞同 展开评论 打赏
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