Android：EditText

Android的编辑框控件EditText在平常编程时会经常用到，有时候会对编辑框增加某些限制，如限制只能输入数字，最大输入的文字个数，不能输入一些非法字符等，这些需求有些可以使用android控件属性直接写在布局xml文件里，比如android:numeric="integer"（只允许输入数字）；

对于一些需求，如非法字符限制（例如不允许输入#号，如果输入了#给出错误提示），做成动态判断更方便一些，而且容易扩展；

在Android里使用TextWatcher接口可以很方便的对EditText进行监听；TextWatcher中有3个函数需要重载：

 public void beforeTextChanged(CharSequence s, int start,                                  int count, int after);    public void onTextChanged(CharSequence s, int start, int before, int count);    public void afterTextChanged(Editable s);

从函数名就可以知道其意思，每当敲击键盘编辑框的文字改变时，上面的三个函数都会执行，beforeTextChanged可以给出变化之前的内容，onTextChanged和afterTextChanged给出追加上新的字符之后的文本；

所以对字符的限制判断可以在afterTextChanged函数中进行，如果检查到新追加的字符为认定的非法字符，则在这里将其delete掉，那么他就不会显示在编辑框里了：

private final TextWatcher mTextWatcher = new TextWatcher() {    public void beforeTextChanged(CharSequence s, int start, int count, int after) {    }     public void onTextChanged(CharSequence s, int start, int before, int count) {    }     public void afterTextChanged(Editable s) {        if (s.length() > 0) {            int pos = s.length() - 1;            char c = s.charAt(pos);            if (c == '#') {//这里限制在字串最后追加#                s.delete(pos,pos+1);                Toast.makeText(MyActivity.this, "Error letter.",Toast.LENGTH_SHORT).show();            }        }    }};

注册监听：

EditText mEditor = (EditText)findViewById(R.id.editor_input);mEditor.addTextChangedListener(mTextWatcher);

android 中如何限制 EditText 最大输入字符数:

方法一：

在 xml 文件中设置文本编辑框属性作字符数限制

如：android:maxLength="10" 即限制最大输入字符个数为10

方法二：

在代码中使用InputFilter 进行过滤

//editText.setFilters(new InputFilter[]{new InputFilter.LengthFilter(20)}); 即限定最大输入字符数为20

[java] view plain copy print ?

public class TextEditActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
EditText editText = (EditText)findViewById(R.id.entry);
editText.setFilters(new InputFilter[]{new InputFilter.LengthFilter(20)});
}
}

public class TextEditActivity extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);                EditText editText = (EditText)findViewById(R.id.entry);        editText.setFilters(new InputFilter[]{new InputFilter.LengthFilter(20)});    }}

方法三：

利用 TextWatcher 进行监听

[java] view plain copy print ?

package cie.textEdit;
import android.text.Editable;
import android.text.Selection;
import android.text.TextWatcher;
import android.widget.EditText;
/*
* 监听输入内容是否超出最大长度，并设置光标位置
* */
public class MaxLengthWatcher implements TextWatcher {
private int maxLen = 0;
private EditText editText = null;
public MaxLengthWatcher(int maxLen, EditText editText) {
this.maxLen = maxLen;
this.editText = editText;
}
public void afterTextChanged(Editable arg0) {
// TODO Auto-generated method stub
}
public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,
int arg3) {
// TODO Auto-generated method stub
}
public void onTextChanged(CharSequence arg0, int arg1, int arg2, int arg3) {
// TODO Auto-generated method stub
Editable editable = editText.getText();
int len = editable.length();
if(len > maxLen)
{
int selEndIndex = Selection.getSelectionEnd(editable);
String str = editable.toString();
//截取新字符串
String newStr = str.substring(0,maxLen);
editText.setText(newStr);
editable = editText.getText();
//新字符串的长度
int newLen = editable.length();
//旧光标位置超过字符串长度
if(selEndIndex > newLen)
{
selEndIndex = editable.length();
}
//设置新光标所在的位置
Selection.setSelection(editable, selEndIndex);
}
}
}

package cie.textEdit;import android.text.Editable;import android.text.Selection;import android.text.TextWatcher;import android.widget.EditText;/* * 监听输入内容是否超出最大长度，并设置光标位置 * */public class MaxLengthWatcher implements TextWatcher {private int maxLen = 0;private EditText editText = null;public MaxLengthWatcher(int maxLen, EditText editText) {this.maxLen = maxLen;this.editText = editText;}public void afterTextChanged(Editable arg0) {// TODO Auto-generated method stub}public void beforeTextChanged(CharSequence arg0, int arg1, int arg2,int arg3) {// TODO Auto-generated method stub}public void onTextChanged(CharSequence arg0, int arg1, int arg2, int arg3) {// TODO Auto-generated method stubEditable editable = editText.getText();int len = editable.length();if(len > maxLen){int selEndIndex = Selection.getSelectionEnd(editable);String str = editable.toString();//截取新字符串String newStr = str.substring(0,maxLen);editText.setText(newStr);editable = editText.getText();//新字符串的长度int newLen = editable.length();//旧光标位置超过字符串长度if(selEndIndex > newLen){selEndIndex = editable.length();}//设置新光标所在的位置Selection.setSelection(editable, selEndIndex);}}}

对应的 activity 部分的调用为：

[java] view plain copy print ?

package cie.textEdit;
import android.app.Activity;
import android.os.Bundle;
import android.text.InputFilter;
import android.widget.EditText;
public class TextEditActivity extends Activity {
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
EditText editText = (EditText) findViewById(R.id.entry);
editText.addTextChangedListener(new MaxLengthWatcher(10, editText));
}
}

package cie.textEdit;import android.app.Activity;import android.os.Bundle;import android.text.InputFilter;import android.widget.EditText;public class TextEditActivity extends Activity {    /** Called when the activity is first created. */    @Override    public void onCreate(Bundle savedInstanceState) {        super.onCreate(savedInstanceState);        setContentView(R.layout.main);EditText editText = (EditText) findViewById(R.id.entry);editText.addTextChangedListener(new MaxLengthWatcher(10, editText));    }}

限制输入字符数为10个

main.xml 文件

[html] view plain copy print ?

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<TextView
android:id="@+id/label"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:text="Type here:"/>
<EditText
android:id="@+id/entry"
android:singleLine="true"
android:layout_width="fill_parent"
android:layout_height="wrap_content"
android:background="@android:drawable/editbox_background"
android:layout_below="@id/label"/>
<Button
android:id="@+id/ok"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_below="@id/entry"
android:layout_alignParentRight="true"
android:layout_marginLeft="10dip"
android:text="OK" />
<Button
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_toLeftOf="@id/ok"
android:layout_alignTop="@id/ok"
android:text="Cancel" />
</RelativeLayout>

<?xml version="1.0" encoding="utf-8"?><RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"    android:layout_width="fill_parent"    android:layout_height="fill_parent">    <TextView        android:id="@+id/label"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:text="Type here:"/>    <EditText        android:id="@+id/entry"        android:singleLine="true"        android:layout_width="fill_parent"        android:layout_height="wrap_content"        android:background="@android:drawable/editbox_background"        android:layout_below="@id/label"/>    <Button        android:id="@+id/ok"        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_below="@id/entry"        android:layout_alignParentRight="true"        android:layout_marginLeft="10dip"        android:text="OK" />    <Button        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_toLeftOf="@id/ok"        android:layout_alignTop="@id/ok"        android:text="Cancel" /></RelativeLayout>

效果为输入了10个字符后，光标停在末尾

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