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

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

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 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);
			
		}
	}

}

对应的 activity 部分的调用为：

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

<?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