Question

我的应用程序有两个活动和一个扩展ArrayAdapter的java文件。

MainActivity.java

package com.prajjwal.myfreight_0;

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.view.View;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.RadioButton;
import android.widget.RadioGroup;
import android.widget.Spinner;
import android.widget.TextView;

public class MainActivity extends Activity {

final String[] comptype ={"Exporter","Shipper","Freight Forwarder","Custom House Agent","Transporter"};
String ss;
TextView tv1,tv2;
RadioGroup rg1;
RadioButton rb1;
Button b1;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    tv1=(TextView)findViewById(R.id.textView1);
    tv2=(TextView)findViewById(R.id.textView2);
    rg1=(RadioGroup)findViewById(R.id.radioGroup1);
    b1=(Button)findViewById(R.id.button1);

    b1.setOnClickListener(new View.OnClickListener() {

        @Override
        public void onClick(View v) {
            // TODO Auto-generated method stub
            final int selid=rg1.getCheckedRadioButtonId(); 
            rb1=(RadioButton)findViewById(selid);
            ss="did";

            if(rb1.getText().toString().equals(comptype[0])) {
                Intent i1=new Intent(MainActivity.this,FreeActivity.class);
                i1.putExtra("did", comptype[0]);
                startActivity(i1);
            }
        }
    });



}

FreeActivity.java

import android.os.Bundle;
import android.app.Activity;
import android.content.Intent;
import android.view.Menu;
import android.widget.ListView;

public class FreeActivity extends Activity {

ListView lw;
final String[] fields={"Name","User Name","E-mail","Company","Company E-mail"};
LoginListView llv1;
String s;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_exp);
    Intent i1;
    i1=getIntent();
    s=i1.getStringExtra("did");

    llv1=new LoginListView(this,fields);
    lw.setAdapter(llv1);


}

LoginListView助手类

package com.prajjwal.myfreight_0;

import android.app.Activity;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ArrayAdapter;
import android.widget.TextView;

public class LoginListView extends ArrayAdapter<String> {

private final Activity a1;
private final String[] s1;

public LoginListView(Activity a, String[] s){
    super(a,R.layout.loginlist,s);
    s1=s;
    a1=a;
}

public View getView(int i,View v,ViewGroup vg) {
    LayoutInflater li=a1.getLayoutInflater();
    View v1=li.inflate(R.layout.loginlist, null, true);
    TextView tv;
    tv=(TextView)v1.findViewById(R.id.textView0);
    tv.setText(s1[i]);
    return v1;
    }

    }

loginlist.xml有一个TableLayout，其中一个TableRow包含一个TextView和一个EditText

activity_exp.xml有一个ListView和一个ImageView。我使用扩展ArrayAdapter的LoginListView类在listview中使用。每当我切换到FreeActivity.class时，我都会得到java.lang.NPE。我似乎无法解决错误。

Answer 1

在使用ListView之前实例化ListView。我很确定您的LogCat会告诉您一些相关信息。

public class FreeActivity extends Activity {

ListView lw;
final String[] fields={"Name","User Name","E-mail","Company","Company E-mail"};
LoginListView llv1;
String s;


@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_exp);
    Intent i1;
    i1=getIntent();
    s=i1.getStringExtra("did");

    llv1=new LoginListView(this,fields);
    lw = new ListView(this);//add this
    lw.setAdapter(llv1);


}

此外，练习使用适当的变量名称以提高可读性。使用毫无意义的字母会让你和我们在努力帮助你时变得困难。

无法在我的Android应用程序中切换活动，获取java.lang.NullPointerexception

1 个答案: