以下是我的Android代码:
package com.example.to_dolsit;
import java.util.ArrayList;
import android.app.Activity;
import android.os.Bundle;
import android.util.Log;
import android.view.KeyEvent;
import android.view.Menu;
import android.view.View;
import android.view.View.OnKeyListener;
import android.widget.ArrayAdapter;
import android.widget.EditText;
import android.widget.ListView;
public class MainActivity extends Activity {
int KeyCode;
ListView myListView = (ListView) findViewById(R.id.listView1);
final EditText myEditText = (EditText) findViewById(R.id.editText1);
String tag = "Events";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
//setContentView(R.layout.activity_main);
Log.d( tag,"ohkkkkkkkkkkkkkkkkkkkkkkkkkkkkk.......................");
// create the list of to do items
final ArrayList<String> todoItems = new ArrayList<String>();
// craeate the array adapter to bind the aray to the list
final ArrayAdapter<String> aa;
aa = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, todoItems);
myListView.setAdapter(aa);
myEditText.setOnKeyListener(new OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
if (event.getAction() == KeyEvent.ACTION_DOWN)
if (KeyCode == KeyEvent.KEYCODE_DPAD_CENTER) {
todoItems.add(0, myEditText.getText().toString());
aa.notifyDataSetChanged();
myEditText.setText("");
return true;
}
return false;
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}
布局代码为: -
<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"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >
<EditText
android:id="@+id/editText1"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:inputType="text"
android:drawableLeft="@drawable/ic_launcher"
android:text="@string/EditText" >
</EditText>
<ListView
android:id="@+id/listView1"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:layout_alignLeft="@+id/editText1"
android:layout_below="@+id/editText1"
android:layout_marginLeft="15dp"
android:layout_marginTop="54dp" >
</ListView>
</RelativeLayout>
它给了我以下错误:
02-14 01:31:31.601: E/AndroidRuntime(10689): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.to_dolsit/com.example.to_dolsit.MainActivity}: java.lang.NullPointerException
02-14 01:31:31.601: E/AndroidRuntime(10689): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1573)
02-14 01:31:31.601: E/AndroidRuntime(10689): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1667)
答案 0 :(得分:0)
您的ListView
最有可能导致nullpointer。在致电findViewById()
之前,请勿致电setContentView()
。将您的代码更改为以下内容。
public class MainActivity extends Activity {
int KeyCode;
String tag = "Events";
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
final ListView myListView = (ListView) findViewById(R.id.listView1);
final EditText myEditText = (EditText) findViewById(R.id.editText1);
// create the list of to do items
final ArrayList<String> todoItems = new ArrayList<String>();
// craeate the array adapter to bind the aray to the list
final ArrayAdapter<String> aa;
aa = new ArrayAdapter<String>(this,
android.R.layout.simple_list_item_1, todoItems);
myListView.setAdapter(aa);
myEditText.setOnKeyListener(new OnKeyListener() {
@Override
public boolean onKey(View v, int keyCode, KeyEvent event) {
// TODO Auto-generated method stub
if (event.getAction() == KeyEvent.ACTION_DOWN) {
if (KeyCode == KeyEvent.KEYCODE_DPAD_CENTER) {
todoItems.add(0, myEditText.getText().toString());
aa.notifyDataSetChanged();
myEditText.setText("");
return true;
}
return false;
}
});
}
@Override
public boolean onCreateOptionsMenu(Menu menu) {
// Inflate the menu; this adds items to the action bar if it is present.
getMenuInflater().inflate(R.menu.main, menu);
return true;
}
}