Android TextWatcher应用实例
(1)使用TextWathcer限制输入字符个数
布局中EditText在android布局中经常用到,对EditText中输入的内容也经常需要进行限制,我们可以通过TextWatcher去观察输入框中输入的内容来限制输入字符个数。
主布局:
<?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:orientation="vertical"> <TextView android:id="@+id/tv" android:layout_width="fill_parent" android:layout_height="wrap_content" android:ellipsize="marquee" android:focusable="true" android:focusableInTouchMode="true" android:marqueeRepeatLimit="marquee_forever" android:scrollHorizontally="true" android:text="Please input the text:" android:textColor="@android:color/white" /> <EditText android:id="@+id/ET" android:layout_width="match_parent" android:layout_height="wrap_content" android:inputType="number" /> </LinearLayout>
Java代码:
package com.android.text; import android.app.Activity; import android.os.Bundle; import android.text.Editable; import android.text.TextWatcher; import android.util.Log; import android.widget.EditText; import android.widget.TextView; import android.widget.Toast; public class TextWatcherDemo extends Activity { private TextView mTextView; private EditText mEditText; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.main); mTextView = (TextView)findViewById(R.id.tv); mEditText = (EditText)findViewById(R.id.ET); mEditText.addTextChangedListener(mTextWatcher); } TextWatcher mTextWatcher = new TextWatcher() { private CharSequence temp; private int editStart ; private int editEnd ; @Override public void beforeTextChanged(CharSequence s, int arg1, int arg2, int arg3) { temp = s; } @Override public void onTextChanged(CharSequence s, int arg1, int arg2, int arg3) { mTextView.setText(s); } @Override public void afterTextChanged(Editable s) { editStart = mEditText.getSelectionStart(); editEnd = mEditText.getSelectionEnd(); if (temp.length() > 10) { Toast.makeText(TextWatcherDemo.this, "你输入的字数已经超过了限制!", Toast.LENGTH_SHORT) .show(); s.delete(editStart-1, editEnd); int tempSelection = editStart; mEditText.setText(s); mEditText.setSelection(tempSelection); } } }; }
(2)使用TextWathcer实现EditeText和TextView同步
TextWatcher自身是一个接口,首先需要实现这个接口并覆盖其三个方法,分别为Text改变之前,改变之后以及改变的过程中各自发生的动作相应,这里我们只需要实现EditText在文本发生改变时候让TextView的内容跟着发生变化。
editText.addTextChangedListener(new TextWatcher(){ @Override public void afterTextChanged(Editable s) { } @Override public void beforeTextChanged(CharSequence s,int start,int count,int after){ } @Override public void onTextChanged(CharSequence s, int start, int before, int count) { textView.setText(editText.getText()); } });
可以看出TextWatcher是专门用来监听文本变化的,正因为它的这个技能,正是我们实现同步的功能所需要的。