android.text.TextWatcher

最新推荐文章于 2021-01-17 17:21:43 发布

原创最新推荐文章于 2021-01-17 17:21:43 发布 · 589 阅读

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本文详细介绍了TextWatcher接口的功能与使用方法，包括beforeTextChanged、onTextChanged及afterTextChanged三个关键方法的作用与参数解释，帮助开发者更好地理解和应用此接口。

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/**
 * 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);
}

说明：

public void beforeTextChanged(CharSequence s, int start, int count, int after)

s改变前的text字符，start当前起始位置，count被替换字符的长度（删除时为0），after新替代字符的长度

public void onTextChanged(CharSequence s, int start, int before, int count)

s改变后的text字符，start替换前的起始位置（同beforeTextChanged），before被替换字符的长度，count新替代字符的长度

public void afterTextChanged(Editable s)

s改变后的text字符