Android应用程序在启动时因onClick上的java.lang.NullPointerException而崩溃
我想让用户点击一个按钮来启动一个对话框。当我点击按钮时,它崩溃了。下面是日志: android.view.view.performClick(view.java:2344)上的com.shoppinglist.shoppinglist$1$2.onClick(shoppinglist.java:50)上的nullpointerexception在android.view.view.onTouchEvent(view.java:4133)上的android.widget.TextView.onTouchEvent(TextView.java:6510)上的dispatchTouchEvent(view.java:3672)android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)的android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)的android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)的android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)的android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)位于android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) 这是我的.java文件:Android应用程序在启动时因onClick上的java.lang.NullPointerException而崩溃,android,crash,Android,Crash,我想让用户点击一个按钮来启动一个对话框。当我点击按钮时,它崩溃了。下面是日志: android.view.view.performClick(view.java:2344)上的com.shoppinglist.shoppinglist$1$2.onClick(shoppinglist.java:50)上的nullpointerexception在android.view.view.onTouchEvent(view.java:4133)上的android.widget.TextView.onTo
package com.shoppinglist;
import java.util.ArrayList;
import android.app.Dialog;
import android.app.ListActivity;
import android.os.Bundle;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.ArrayAdapter;
import android.widget.Button;
import android.widget.EditText;
import android.widget.ListView;
public class ShoppingList extends ListActivity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final EditText et = (EditText) findViewById(R.id.edittext);
ListView lv = (ListView) findViewById(android.R.id.list);
final ArrayList<String> items = new ArrayList<String>();
final ArrayAdapter<String> adapter;
adapter = new ArrayAdapter<String>(
this, android.R.layout.simple_list_item_1, items);
lv.setAdapter(adapter);
Button button1main = (Button) findViewById(R.id.add);
button1main.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
final Dialog additem = new Dialog(ShoppingList.this);
additem.setContentView(R.layout.maindialog);
additem.setTitle("Type your item");
additem.setCancelable(true);
et.setHint("Type the name of an item...");
Button button = (Button) findViewById(R.id.cancel);
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
additem.dismiss();
}
});
additem.show();
Button ok = (Button) findViewById(R.id.ok);
ok.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
items.add(et.getText().toString());
adapter.notifyDataSetChanged();
additem.dismiss();
et.setText("");
}
}
);
}
});
}
}
package.com.shoppinglist;
导入java.util.ArrayList;
导入android.app.Dialog;
导入android.app.ListActivity;
导入android.os.Bundle;
导入android.view.view;
导入android.view.view.OnClickListener;
导入android.widget.ArrayAdapter;
导入android.widget.Button;
导入android.widget.EditText;
导入android.widget.ListView;
公共类ShoppingList扩展了ListActivity{
/**在首次创建活动时调用*/
@凌驾
创建时的公共void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
最终EditText et=(EditText)findViewById(R.id.EditText);
ListView lv=(ListView)findViewById(android.R.id.list);
最终ArrayList项=新ArrayList();
最终阵列适配器;
适配器=新阵列适配器(
这,android.R.layout.simple_list_item_1,items);
低压设置适配器(适配器);
按钮button1main=(按钮)findViewById(R.id.add);
button1main.setOnClickListener(新的OnClickListener(){
@凌驾
公共void onClick(视图v){
最终对话框additem=新对话框(ShoppingList.this);
additem.setContentView(R.layout.maindialog);
additem.setTitle(“键入您的项目”);
additem.setCancelable(真);
et.setHint(“键入项目名称…”);
按钮按钮=(按钮)findViewById(R.id.cancel);
setOnClickListener(新的OnClickListener(){
@凌驾
公共void onClick(视图v){
additem.discouse();
}
});
additem.show();
按钮ok=(按钮)findViewById(R.id.ok);
ok.setOnClickListener(新的OnClickListener(){
@凌驾
公共void onClick(视图v){
添加(et.getText().toString());
adapter.notifyDataSetChanged();
additem.discouse();
et.setText(“”);
}
}
);
}
});
}
}
下面是我的main.xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#FF9900"
android:padding="10dp"
android:orientation="vertical">
<Button
android:id="@+id/add"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Add item..."
android:layout_gravity="center"/>
<ListView android:id="@android:id/list"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:background="#FFCC00"/>
</LinearLayout>
下面是我的对话框xml:
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:id="@+id/layout_root"
android:orientation="vertical"
android:background="#FFFFFF"
android:minHeight="100dp"
android:minWidth="300dp">
<EditText
android:id="@+id/edittext"
android:layout_width="fill_parent"
android:layout_height="wrap_content"/>
<LinearLayout
android:id="@+id/button_layout"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:orientation="horizontal"
android:layout_gravity="bottom">
<Button
android:id="@+id/ok"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Ok"/>
<Button
android:id="@+id/cancel"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Cancel"/>
</LinearLayout>
</LinearLayout>
如果我的行号正确,则此块中会出现空指针异常:
new OnClickListener() {
@Override
public void onClick(View v) {
items.add(et.getText().toString());
adapter.notifyDataSetChanged();
additem.dismiss();
et.setText("");
}
错误是您正在访问的变量之一为空。在此函数中,您将访问et、et.getText()、项、适配器和additem。我建议调试此部分(通过eclipse或打印日志语句)以确定哪个项为空。如果我的行号正确,则此块中会出现空指针异常:
new OnClickListener() {
@Override
public void onClick(View v) {
items.add(et.getText().toString());
adapter.notifyDataSetChanged();
additem.dismiss();
et.setText("");
}
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final EditText et = (EditText) findViewById(R.id.edittext);
ListView lv = (ListView) findViewById(android.R.id.list);
final ArrayList<String> items = new ArrayList<String>();
final ArrayAdapter<String> adapter;
adapter = new ArrayAdapter<String>(
this, android.R.layout.simple_list_item_1, items);
lv.setAdapter(adapter);
Button button1main = (Button) findViewById(R.id.add);
错误是您正在访问的变量之一为空。在此函数中,您将访问et、et.getText()、项、适配器和additem。我建议调试这个部分(通过eclipse或打印日志语句)以确定哪个项为空
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
final EditText et = (EditText) findViewById(R.id.edittext);
ListView lv = (ListView) findViewById(android.R.id.list);
final ArrayList<String> items = new ArrayList<String>();
final ArrayAdapter<String> adapter;
adapter = new ArrayAdapter<String>(
this, android.R.layout.simple_list_item_1, items);
lv.setAdapter(adapter);
Button button1main = (Button) findViewById(R.id.add);
et
将为null
,对et
的任何方法调用都将导致NullPointerException
编辑
试试这个:
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView lv = (ListView) findViewById(android.R.id.list);
final ArrayList<String> items = new ArrayList<String>();
final ArrayAdapter<String> adapter;
adapter = new ArrayAdapter<String>(
this, android.R.layout.simple_list_item_1, items);
lv.setAdapter(adapter);
Button button1main = (Button) findViewById(R.id.add);
button1main.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
final Dialog additem = new Dialog(ShoppingList.this);
additem.setContentView(R.layout.maindialog);
final EditText et = (EditText)additem.findViewById(R.id.edittext);
additem.setTitle("Type your item");
additem.setCancelable(true);
et.setHint("Type the name of an item...");
Button button = (Button) additem.findViewById(R.id.cancel);
button.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
additem.dismiss();
}
});
additem.show();
Button ok = (Button) additem.findViewById(R.id.ok);
ok.setOnClickListener(new OnClickListener() {
@Override
public void onClick(View v) {
items.add(et.getText().toString());
adapter.notifyDataSetChanged();
additem.dismiss();
et.setText("");
}
});
}
});
@覆盖
创建时受保护的void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
ListView lv=(ListView)findViewById(android.R.id.list);
最终ArrayList项=新ArrayList();
最终阵列适配器;
适配器=新阵列适配器(
这,android.R.layout.simple_list_item_1,items);
低压设置适配器(适配器);
按钮button1main=(按钮)findViewById(R.id.add);
button1main.setOnClickListener(新的OnClickListener(){
@凌驾
公共void onClick(视图v){
最终对话框additem=新对话框(ShoppingList.this);
additem.setContentView(R.layout.maindialog);
最终EditText et=(EditText)additem.findViewById(R.id.EditText);
additem.setTitle(“键入您的项目”);
additem.setCancelable(真);
et.setHint(“键入项目名称…”);
Button Button=(Button)additem.findViewById(R.id.cancel);
setOnClickListener(新的OnClickListener(){
@凌驾
公共void onClick(视图v){
additem.discouse();
}
});
additem.show();
按钮ok=(按钮)additem.findViewById(R.id.ok);
ok.setOnClickListener(新的OnClickListener(){
@凌驾
公共void onClick(视图v){
添加(et.getText().toString());
adapter.notifyDataSetChanged();
additem.discouse();
et.setText(“”);
}
});
}
});
et
将为null
,对et
的任何方法调用都将导致NullPointerException
编辑