Android学习笔记之为Dialog自定义布局，并说明空指针问题

在使用自定义布局时经常会碰见这样的问题：edit = (EditText) findViewById(R.id.edit);并不能获取到控件对象；

在后面代码中使用edit时会报错，空指针异常。意思是edit为null。

解决方案：

LayoutInflater factory = LayoutInflater.from(MyDialogActivity.this);
		final View view = factory.inflate(R.layout.dialog, null);
		edit = (EditText) view.findViewById(R.id.edit);

<pre class="java" name="code" style="background-color: rgb(255, 255, 255); font-family: System; font-size: 13px; line-height: 26px; text-align: left;"><pre class="java" name="code" style="background-color: rgb(255, 255, 255); font-family: System; font-size: 13px; line-height: 26px; text-align: left;"><pre class="java" name="code" style="background-color: rgb(255, 255, 255); font-family: System;"><pre class="java" name="code" style="background-color: rgb(255, 255, 255); font-family: System;"><span style="font-size: 13px; line-height: 26px; text-align: left;">MyDialogActivity.java 文件名称 MyDialogActivity.java</span></pre></pre></pre></pre>

R.layout.dialog：自定义布局文件 dialog.xml
如何为Dialog布局呢？
你需要定义一个布局文件，我在例子中定义了一个：dialog.xml

final View view = factory.inflate(R.layout.dialog, null);

得到view，用setView(view);方法设置布局。

具体实现：

dialog.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/dialogLayout"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:gravity="center_horizontal"
    android:orientation="vertical" >

    <EditText
        android:id="@+id/edit"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        android:gravity="top"
        android:lines="4"
        android:maxLines="4" />

</LinearLayout>

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:gravity="center_horizontal"
    android:orientation="vertical" >
    
    <TextView
        android:id="@+id/textView"
        android:layout_width="fill_parent"
        android:layout_height="wrap_content"
        />

</LinearLayout>

MyDialogActivity.java

package xiaosi.mydialog;

import android.app.Activity;
import android.app.AlertDialog;
import android.content.DialogInterface;
import android.content.DialogInterface.OnClickListener;
import android.os.Bundle;
import android.view.LayoutInflater;
import android.view.View;
import android.widget.EditText;
import android.widget.TextView;

public class MyDialogActivity extends Activity
{
	/** Called when the activity is first created. */
	private EditText edit = null;
    private TextView textview = null;
	@Override
	public void onCreate(Bundle savedInstanceState)
	{
		super.onCreate(savedInstanceState);
		setContentView(R.layout.main);
		textview = (TextView)findViewById(R.id.textView);
		LayoutInflater factory = LayoutInflater.from(MyDialogActivity.this);
		final View view = factory.inflate(R.layout.dialog, null);
		edit = (EditText) view.findViewById(R.id.edit);
		AlertDialog.Builder builder = new AlertDialog.Builder(
				MyDialogActivity.this);
		builder.setTitle("文字效果");
		builder.setIcon(R.drawable.btn_mainmenu_words_a);
		builder.setMessage("请输入你要的文字:");
		builder.setView(view);
		builder.setPositiveButton("提交", new SubmitListener());
		builder.setNegativeButton("取消", new DismissListener());
		builder.show();
	}

	private class SubmitListener implements OnClickListener
	{
		public void onClick(DialogInterface dialog, int which)
		{
			System.out.println(edit.getText().toString());
			textview.setText("测试结果:\n" + edit.getText().toString());
			dialog.dismiss();
		}
	}
	
	private class DismissListener implements OnClickListener
	{
		public void onClick(DialogInterface dialog, int which)
		{
			dialog.dismiss();
		}
	}
}