[英]Null pointer exception while using Parcelable
我做了一个Java类'store',它只存储我通过2个微调器提供的值和一个edittext ...我使用parcelable将此类的对象传递给中间类Spinpizza.java和Bill.java ... 。它将显示正确的输出,直到SpinPizza ..(显示通过spinner n edittext输入的值),但它在Bill.java中给出了NULL POINTER EXCEPTION::-(请帮助我...我坚持了4天以上。 。
这是我的代码...
Store.java
package com.Lak;
import android.os.Parcel;
import android.os.Parcelable;
public class store implements Parcelable {
/**
*
*/
private static final long serialVersionUID = 1L;
private String pizzaname;
private String pizzasize;
private int n;
public void setOrder(String name,String size,int qty)
{
pizzaname = name;
pizzasize = size;
n = qty;
}
public String getPizzaName()
{
return pizzaname;
}
public int getQuantity()
{return n;}
public String getPizzaSize() {
// TODO Auto-generated method stub
return pizzasize;
}
public int describeContents() {
// TODO Auto-generated method stub
return 0;
}
@SuppressWarnings("rawtypes")
public static final Parcelable.Creator CREATOR = new Parcelable.Creator() {
public store createFromParcel(Parcel in) {
return new store(in);
}
public store[] newArray(int size) {
return new store[size];
}
};
public void writeToParcel(Parcel dest, int flags) {
dest.writeInt(n);
dest.writeString(pizzaname);
dest.writeString(pizzasize);
}
public store()
{}
public store(Parcel source){
/*
* Reconstruct from the Parcel
*/
n = source.readInt();
pizzaname = source.readString();
pizzasize = source.readString();
}
/** Called when the activity is first created. */
}
(SpinPizza.java)
package com.Lak;
import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.KeyEvent;
import android.view.View;
import android.view.View.OnKeyListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Spinner;
import android.widget.TextView;
import android.widget.Toast;
public class SpinPizza extends Activity{
/**
*
*/
private static final long serialVersionUID = 1L;
store B[]= new store[10];
Spinner s=null,s1=null;
EditText edittext=null;
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.drop);
s = (Spinner) findViewById(R.id.spinner);
ArrayAdapter<?> adapter = ArrayAdapter.createFromResource(
this, R.array.pizzaarray, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
s.setAdapter(adapter);
s1 = (Spinner) findViewById(R.id.spinner1);
ArrayAdapter<?> adapter1 = ArrayAdapter.createFromResource(
this, R.array.sizearray, android.R.layout.simple_spinner_item);
adapter.setDropDownViewResource(android.R.layout.simple_spinner_dropdown_item);
s1.setAdapter(adapter1);
edittext = (EditText) findViewById(R.id.edittext);
edittext.setOnKeyListener(new OnKeyListener() {
public boolean onKey(View v, int keyCode, KeyEvent event) {
// If the event is a key-down event on the "enter" button
if ((event.getAction() == KeyEvent.ACTION_DOWN) &&
(keyCode == KeyEvent.KEYCODE_ENTER || keyCode == KeyEvent.KEYCODE_DPAD_CENTER)) {
// Perform action on key press
int i=0;
B[i]=new store();
int n=Integer.parseInt(edittext.getText().toString());
B[i].setOrder(s.getSelectedItem().toString(), s1.getSelectedItem().toString(),n );
TextView objText=(TextView) findViewById(R.id.pl);
TextView objText1=(TextView) findViewById(R.id.pl2);
objText.setText(B[i].getPizzaName());
objText1.setText(B[i].getPizzaSize());
i++;
Toast.makeText(SpinPizza.this, edittext.getText(), Toast.LENGTH_SHORT).show();
return true;
}
return false;
}
});
Button next1 = (Button) findViewById(R.id.bill);
next1.setOnClickListener(new View.OnClickListener() {
public void onClick(View view) {
Intent myIntent = new Intent(view.getContext(), Bill.class);
for(int i =0;i<B.length;i++)
{
myIntent.putExtra("myclass"+i,B[i]);
}
myIntent.putExtra("length",B.length);
startActivityForResult(myIntent, 0);
}
});
}
}
(Bill.java)
package com.Lak;
import android.app.Activity;
import android.os.Bundle;
import android.view.ViewGroup.LayoutParams;
import android.widget.TableLayout;
import android.widget.TableRow;
import android.widget.TextView;
public class Bill extends Activity {
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
this.setContentView(R.layout.calc);
store B[] = new store[10];
Bundle bj=getIntent().getExtras();
int length = bj.getInt("length");
for(int i = 0 ;i<length;i++)
{
B[i] = (store)bj.getParcelable("myClass"+i);
}
// B = (store[]) bj.get("myClass");
/* Find Tablelayout defined in main.xml */
TableLayout tl = (TableLayout)findViewById(R.id.myTable);
/* Create a new row to be added. */
TableRow tr = new TableRow(this);
tr.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
/* Create TEXTVIEWS to be the row-content. */
for(int i=0;i<length;i++)
{ TextView b = new TextView(this);
b.setText(B[i].getPizzaName()); // NULL POINTER EXCEPTION :(
TextView b1 = new TextView(this);
b1.setText(B[i].getPizzaSize());
TextView b2 = new TextView(this);
b2.setText(B[i].getQuantity());
b.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
b1.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
b2.setLayoutParams(new LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
/* Add TextViews to row. */
tr.addView(b);
tr.addView(b1);
tr.addView(b2);
/* Add row to TableLayout. */
tl.addView(tr,new TableLayout.LayoutParams(
LayoutParams.FILL_PARENT,
LayoutParams.WRAP_CONTENT));
}}
}
好吧,如果此行引发异常:
b.setText(B[i].getPizzaName());
然后的选项是:
b
为null(绝对不是;在前一行中为其分配了非null值) B
为空 B[i]
为空 我的钱就到最后了。 这是初始化数组的方式:
for(int i = 0 ;i<length;i++)
{
B[i] = (store)bj.getParcelable("myClass"+i);
}
有什么说法说getParcelable
不会返回null吗?
返回与给定键关联的值;如果不存在给定键的所需类型的映射,或者为该键显式关联一个空值,则返回null。
所以我的猜测是getParcelable
返回null。 现在,您需要找出原因并进行修复。 我还建议为类和变量使用更常规和更具描述性的名称。
这篇文章很老,但是这里最常见的问题是为您的类实现Parcelable接口,然后触摸字段和方法,这可能需要您重新实现Parcelable接口或仅添加缺失的接口。
我建议您为Android Studio或Eclipse安装Parcelable插件,然后重新创建样板。
确实,这是一个非常古老的问题,但我是通过简单的搜索于2018年到达这里的,并且正在使用Kotlin,因此将来会对此进行回答。
您实际上无法对final \\ val字段进行修改,因为Parcelable接口无法在其中写入和重新写入其中的值,要么丢弃final \\ val字段,要么不将它们与您的包裹方案合并。
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