Dialog的使用(一)：用AlertDialog提示

用户输入一个地址，当查询位置失败时，弹出对话框

package com.example.androidtest;

import android.os.Bundle;
import android.app.Activity;
import android.app.AlertDialog;
import android.content.Intent;
import android.net.Uri;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.util.Log;

public class MainActivity extends Activity {
	
	public void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		
		final AlertDialog.Builder adb = new AlertDialog.Builder(this);
		final EditText addressfield = (EditText)findViewById(R.id.address);
		final Button button = (Button)findViewById(R.id.launchmap);
		button.setOnClickListener(new Button.OnClickListener() {
			public void onClick(View v) 
			{
				try {
					String address = addressfield.getText().toString();
					address = address.replace(' ', '+');
					Intent geoIntent = new Intent(Intent.ACTION_VIEW, Uri.parse("geo:0,0?q=" + address));
					startActivity(geoIntent);
				} catch (Exception e) {
					AlertDialog ad = adb.create();
					ad.setMessage("Failed to launch");
					ad.show();
				}
			}
		});
	}	
}

activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:orientation="vertical"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    >
<TextView  
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="Please enter your home address."
    />
<EditText
  android:id="@+id/address"
    android:layout_width="fill_parent" 
    android:layout_height="wrap_content" 
  android:autoText="true"
  />
<Button
  android:id="@+id/launchmap"
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content"
    android:text="Show Map"
    /> 
<TextView  
    android:layout_width="wrap_content" 
    android:layout_height="wrap_content" 
    android:text="Unlocking Android"
    />
</LinearLayout>