Android addTextChangedListener方法介绍

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文本变化监听器addTextChangedListener中TextWatcher方法三个方法意义

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EditText editText = findViewById(R.id.et_test);
editText.addTextChangedListener(new TextWatcher() {
// charSequence为在你按键之前显示的字符串
start为新字符串与charSequence开始出现差异的下标
count表示原字符串的count个字符
after表示将会被after个字符替换
@Override
public void beforeTextChanged(CharSequence charSequence, int start, int count, int after) {
Log.i(TAG, "beforeTextChanged: charSequence=" + charSequence + ", start=" + start + ", count=" + count + ", after=" + after);
}
// 按键之前字符串的start位置的before个字符已经被count个字符替换形成新字符串charSequence
@Override
public void onTextChanged(CharSequence charSequence, int start, int before, int count) {
Log.i(TAG, "onTextChanged: charSequence=" + charSequence + ", start=" + start + ", before=" + before + ", count=" + count);
}
// afterTextChanged中 editable为EditText显示的内容
@Override
public void afterTextChanged(Editable editable) {
Log.i(TAG, "afterTextChanged: editable=" + editable);
}
});

通过上面注释已经可以理解了,此处附上测试log

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// 输入a
com.nan.myapplication I/breeze: beforeTextChanged: s=, start=0, count=0, after=1
com.nan.myapplication I/breeze: onTextChanged: s=a, start=0, before=0, count=1
// 继续输入b
com.nan.myapplication I/breeze: beforeTextChanged: s=a, start=1, count=0, after=1
com.nan.myapplication I/breeze: onTextChanged: s=ab, start=1, before=0, count=1
// 继续输入GG
com.nan.myapplication I/breeze: beforeTextChanged: s=ab, start=2, count=0, after=2
com.nan.myapplication I/breeze: onTextChanged: s=abGG, start=2, before=0, count=2
// 删除最后一个G
com.nan.myapplication I/breeze: beforeTextChanged: s=abGG, start=3, count=1, after=0
com.nan.myapplication I/breeze: onTextChanged: s=abG, start=3, before=1, count=0
// 将bG选中替换为嘿嘿
com.nan.myapplication I/breeze: beforeTextChanged: s=abG, start=1, count=2, after=2
com.nan.myapplication I/breeze: onTextChanged: s=a嘿嘿, start=1, before=2, count=2