我想让它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。这是日志:
nullpointerexception at com.shoppinglist.ShoppingList$1$2.onClick(ShoppingList.java:50) at android.view.View.performClick(View.java:2344) at android.view.View.onTouchEvent(View.java:4133) at android.widget.TextView.onTouchEvent(TextView.java:6510) at android.view.View.dispatchTouchEvent(View.java:3672) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882) at android.view.ViewGroup.dispatchTouchEvent(ViewGroup.java:882)
这是我的 .java 文件:
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("");
}
}
);
}
});
}
}
这是我的 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>
这是我的对话框 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>
最佳答案
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);
在您的代码中,您使用 setContentView
到 R.layout.main
。然后你尝试在 R.layout.main
中找到 R.id.edittext
但 edittext
存在于 maindialog.xml
。
所以当你调用
final EditText et = (EditText) findViewById(R.id.edittext);
et
将为 null
并且对 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("");
}
});
}
});
关于由于 onClick 处出现 java.lang.NullPointerException,Android 应用程序在启动时崩溃,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/4775812/