首先来看一下TextWatcher的源代码
package android.text; /**
* When an object of a type is attached to an Editable, its methods will
* be called when the text is changed.
*/
public interface TextWatcher extends NoCopySpan {
/**
* This method is called to notify you that, within <code>s</code>,
* the <code>count</code> characters beginning at <code>start</code>
* are about to be replaced by new text with length <code>after</code>.
* It is an error to attempt to make changes to <code>s</code> from
* this callback.
*/
public void beforeTextChanged(CharSequence s, int start,
int count, int after);
/**
* This method is called to notify you that, within <code>s</code>,
* the <code>count</code> characters beginning at <code>start</code>
* have just replaced old text that had length <code>before</code>.
* It is an error to attempt to make changes to <code>s</code> from
* this callback.
*/
public void onTextChanged(CharSequence s, int start, int before, int count); /**
* This method is called to notify you that, somewhere within
* <code>s</code>, the text has been changed.
* It is legitimate to make further changes to <code>s</code> from
* this callback, but be careful not to get yourself into an infinite
* loop, because any changes you make will cause this method to be
* called again recursively.
* (You are not told where the change took place because other
* afterTextChanged() methods may already have made other changes
* and invalidated the offsets. But if you need to know here,
* you can use {@link Spannable#setSpan} in {@link #onTextChanged}
* to mark your place and then look up from here where the span
* ended up.
*/
public void afterTextChanged(Editable s);
}
下面通过通过一个小实例来学习TextWatcher的相关用法
实现该接口
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) {
mDetailView.setText(s);
}
@Override
public void afterTextChanged(Editable s) {
editStart = mEditText.getSelectionStart();
editEnd = mEditText.getSelectionEnd();
if (temp.length() > 11) {
Toast.makeText(MainActivity.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);
}
}
};再注册这个监听
TextView mDetailView;
EditText mEditText; @Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
mDetailView = (TextView) findViewById(R.id.mDetailView);
mEditText = (EditText) findViewById(R.id.mEditText);
mEditText.addTextChangedListener(mTextWatcher);
}
看运行效果
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作者：欧阳鹏 欢迎转载，与人分享是进步的源泉！
转载请保留原文地址：http://blog.csdn.net/ouyang_peng
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