本方法基于Dialog，使用自定义布局，更能满足发杂的需求。

布局文件：dialog_must_enter.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:layout_margin="@dimen/activity_horizontal_margin" >

    <TextView
        android:id="@+id/txtUsername"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/edtUsername"
        android:layout_alignParentLeft="true"
        android:layout_alignParentTop="true"
        android:gravity="center"
        android:text="姓名: " />

    <EditText
        android:id="@+id/edtUsername"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentRight="true"
        android:layout_alignParentTop="true"
        android:layout_toRightOf="@+id/txtUsername"
        android:ems="10" >

        <requestFocus />
    </EditText>

    <TextView
        android:id="@+id/txtHorizontalCenter"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignBottom="@+id/btnOK"
        android:layout_below="@+id/edtUsername"
        android:layout_centerHorizontal="true"
        android:text="" />

    <Button
        android:id="@+id/btnOK"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_below="@+id/edtUsername"
        android:layout_toLeftOf="@+id/txtHorizontalCenter"
        android:text="确定" />

    <Button
        android:id="@+id/btnCancel"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignTop="@+id/txtHorizontalCenter"
        android:layout_toRightOf="@+id/txtHorizontalCenter"
        android:text="取消" />

</RelativeLayout>

Java代码：

import android.app.Activity;
import android.app.Dialog;
import android.os.Bundle;
import android.text.TextUtils;
import android.view.View;
import android.view.View.OnClickListener;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

public class MainActivity extends Activity {
	private Button btnOpenDialog;
	private Activity activity;


	@Override
	protected void onCreate(Bundle savedInstanceState) {
		super.onCreate(savedInstanceState);
		setContentView(R.layout.activity_main);
		activity = this;
		btnOpenDialog = (Button) findViewById(R.id.btnOpenDialog);
		btnOpenDialog.setOnClickListener(new OnClickListener() {

			@Override
			public void onClick(View v) {
				final Dialog dialog = new Dialog(activity);
				dialog.setContentView(R.layout.dialog_must_enter);
				dialog.setTitle("必填项Demo");

				final EditText edtUserName = (EditText) dialog.findViewById(R.id.edtUsername);
				Button btnOKOfDialog = (Button) dialog.findViewById(R.id.btnOK);
				btnOKOfDialog.setOnClickListener(new OnClickListener() {
					@Override
					public void onClick(View v) {
						if (!TextUtils.isEmpty(edtUserName.getText().toString().trim())) {
							dialog.dismiss();
						} else {
							Toast.makeText(activity, "姓名不能为空！", Toast.LENGTH_LONG).show();
						}

					}
				});

				Button btnCancelOfDialog = (Button) dialog.findViewById(R.id.btnCancel);
				btnCancelOfDialog.setOnClickListener(new OnClickListener() {
					@Override
					public void onClick(View v) {
						dialog.dismiss();
					}
				});

				dialog.show();

			}
		});
	}
}

    _textField.frame = CGRectMake(0, 0, 200, 50);
    _textField.delegate = self;
    _textField.text = str;
    
    [_textField becomeFirstResponder];
    
    
    /*
     设置背景色、背景图片。设置了背景图片后，背景色设置无效
     如果background为nil，disabledBackground无效
     */
    _textField.background = [UIImage imageNamed:@"返回-按下"];
    _textField.disabledBackground = [UIImage imageNamed:@"返回-未激活"];
//    _textField.enabled = NO;
    _textField.backgroundColor = [UIColor blueColor];
    _textField.placeholder = @"输入文本…";
    
    /*
     设置为YES时文本会自动缩小以适应文本窗口大小.默认是保持原来大小,而让长文本滚动
     */
    _textField.adjustsFontSizeToFitWidth = YES;
    //设置自动缩小显示的最小字体大小，adjustsFontSizeToFitWidth为YES才会起作用
    _textField.minimumFontSize = 20;
    _textField.font = [UIFont systemFontOfSize:30.0f];
    
    /*
     内容对齐方式
     内容的垂直对齐方式  UITextField继承自UIControl,此类中有一个属性contentVerticalAlignment
     */
    _textField.textAlignment = UITextAlignmentLeft;
    _textField.contentVerticalAlignment = UIControlContentVerticalAlignmentCenter;
    
    /*
     typedef enum {
     UITextBorderStyleNone,
     UITextBorderStyleLine,
     UITextBorderStyleBezel,
     UITextBorderStyleRoundedRect
     } UITextBorderStyle;
     */
    _textField.borderStyle = UITextBorderStyleBezel;

    /*
     每输入一个字符就变成点 用语密码输入
     */
    _textField.secureTextEntry = NO;
    
    /*
     //输入框中是否有个叉号，在什么时候显示，用于一次性删除输入框中的内容
     typedef enum {
     UITextFieldViewModeNever,　重不出现
     UITextFieldViewModeWhileEditing, 编辑时出现
     UITextFieldViewModeUnlessEditing,　除了编辑外都出现
     UITextFieldViewModeAlways 　一直出现
     } UITextFieldViewMode;
     */
    _textField.clearButtonMode = UITextFieldViewModeWhileEditing;
    
    /*
     开始编辑，清空数据
     */
    _textField.clearsOnBeginEditing = NO;
    
    /*
     //是否纠错
     typedef enum {
     UITextAutocorrectionTypeDefault, 默认
     UITextAutocorrectionTypeNo, 　不自动纠错
     UITextAutocorrectionTypeYes,　自动纠错
     } UITextAutocorrectionType;
     */
    _textField.autocorrectionType = UITextAutocorrectionTypeYes;
    
    /*
     //首字母是否大写
     typedef enum {
     UITextAutocapitalizationTypeNone, 不自动大写
     UITextAutocapitalizationTypeWords,　单词首字母大写
     UITextAutocapitalizationTypeSentences,　句子的首字母大写
     UITextAutocapitalizationTypeAllCharacters, 所有字母都大写
     } UITextAutocapitalizationType;
     */
    _textField.autocapitalizationType = UITextAutocapitalizationTypeWords;
    
    /*
     键盘
     typedef enum {
     UIKeyboardTypeDefault,     　默认键盘，支持所有字符
     UIKeyboardTypeASCIICapable,　支持ASCII的默认键盘
     UIKeyboardTypeNumbersAndPunctuation,　标准电话键盘，支持＋＊＃字符
     UIKeyboardTypeURL,            URL键盘，支持.com按钮 只支持URL字符
     UIKeyboardTypeNumberPad,            　数字键盘
     UIKeyboardTypePhonePad,　 　电话键盘
     UIKeyboardTypeNamePhonePad, 　电话键盘，也支持输入人名
     UIKeyboardTypeEmailAddress, 　用于输入电子 邮件地址的键盘
     UIKeyboardTypeDecimalPad,   　数字键盘 有数字和小数点
     UIKeyboardTypeTwitter,      　优化的键盘，方便输入@、#字符
     UIKeyboardTypeAlphabet = UIKeyboardTypeASCIICapable,
     } UIKeyboardType;
     */
    _textField.keyboardType = UIKeyboardTypeDefault;
    
    /*
     //return键变成什么键
     typedef enum {
     UIReturnKeyDefault, 默认 灰色按钮，标有Return
     UIReturnKeyGo,    　标有Go的蓝色按钮
     UIReturnKeyGoogle,标有Google的蓝色按钮，用语搜索
     UIReturnKeyJoin,标有Join的蓝色按钮
     UIReturnKeyNext,标有Next的蓝色按钮
     UIReturnKeyRoute,标有Route的蓝色按钮
     UIReturnKeySearch,标有Search的蓝色按钮
     UIReturnKeySend,标有Send的蓝色按钮
     UIReturnKeyYahoo,标有Yahoo的蓝色按钮
     UIReturnKeyYahoo,标有Yahoo的蓝色按钮
     UIReturnKeyEmergencyCall, 紧急呼叫按钮
     } UIReturnKeyType;
     */
    _textField.returnKeyType = UIReturnKeyDone;
    
    /*
     //键盘外观
     typedef enum {
     UIKeyboardAppearanceDefault， 默认外观，浅灰色
     UIKeyboardAppearanceDark，　 　深灰 石墨色
     UIKeyboardAppearanceLight 浅灰色
     } UIReturnKeyType;
     */
    _textField.keyboardAppearance=UIKeyboardAppearanceDefault;
    
    /*
     设置左右的两个view
     */
//    UIImageView *imgView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image_right"]];
//    imgView.frame = CGRectMake(0, 0, 20, 20);
//    _textField.rightView = imgView;
//    _textField.rightViewMode = UITextFieldViewModeAlways;   // 同上
    
    UIImageView *imgView = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"image_left"]];
    imgView.frame = CGRectMake(0, 0, 20, 20);
    _textField.leftView = imgView;
    _textField.leftViewMode = UITextFieldViewModeAlways;   // 同上
    
    
    /*
     重写绘制行为
     除了UITextField对象的风格选项，你还可以定制化UITextField对象，为他添加许多不同的重写方法，来改变文本字段的显示行为。这些方法都会返回一个CGRect结构，制定了文本字段每个部件的边界范围。以下方法都可以重写。
     
     – textRectForBounds:　　  　//重写来重置文字区域
     – drawTextInRect:　　      　//改变绘文字属性.重写时调用super可以按默认图形属性绘制,若自己完全重写绘制函数，就不用调用super了.
     – placeholderRectForBounds:　　//重写来重置占位符区域
     – drawPlaceholderInRect:　　//重写改变绘制占位符属性.重写时调用super可以按默认图形属性绘制,若自己完全重写绘制函数，就不用调用super了.
     – borderRectForBounds:　　//重写来重置边缘区域
     – editingRectForBounds:　　//重写来重置编辑区域
     – clearButtonRectForBounds:　　//重写来重置clearButton位置,改变size可能导致button的图片失真
     – leftViewRectForBounds:
     – rightViewRectForBounds:
     */

UITextField使用小结（二）

http://quding0308.iteye.com/admin/blogs/1681180