Android开发，addlistener和setlistener的区别
做Android开发稍微久一点的都知道，android之前的监听器基本都是setlistener，比如setOnClickListener，setTextChangeListener。
但是后来，android中很多的setlistener都被废弃了，用addlistener来替代，比如上面的setTextChangeListener。
本文主要就是用于探讨setlistener和addlistener的区别。
我们就以setOnClickListener和addTextChangedListener举例
1、查看源码
/**
* Register a callback to be invoked when this view is clicked. If this view is not
* clickable, it becomes clickable.
*
* @param l The callback that will run
*
* @see #setClickable(boolean)
*/
public void setOnClickListener(@Nullable OnClickListener l) {
if (!isClickable()) {
setClickable(true);
}
getListenerInfo().mOnClickListener = l;
}/**
* Adds a TextWatcher to the list of those whose methods are called
* whenever this TextView's text changes.
*
* In 1.0, the {@link TextWatcher#afterTextChanged} method was erroneously
* not called after {@link #setText} calls. Now, doing {@link #setText}
* if there are any text changed listeners forces the buffer type to
* Editable if it would not otherwise be and does call this method.
*/
public void addTextChangedListener(TextWatcher watcher) {
if (mListeners == null) {
mListeners = new ArrayList();
}
mListeners.add(watcher);
}
而addListener是将该listener添加到了一个arraylsit集合里面。
从这里我们可以猜测，setListener只能设置一个，addListenr可以设置多个。
下面我们来看看具体。
2、测试setListener
我在xml中设置了一个按钮class ListenerTestActivity : AppCompatActivity() {
override fun onCreate(savedInstanceState: Bundle?) {
super.onCreate(savedInstanceState)
setContentView(R.layout.activity_listener_test)
btn_test_setListener.setOnClickListener {
Log.e("set1", "1-listener is clicked")
}
btn_test_setListener.setOnClickListener {
Log.e("set2", "2-listener is clicked")
}
}
}可以看到，我连续设置了两个点击事件给按钮。
11-08 11:10:56.508 16788-16788/com.stanny.xbtest E/set2: 2-listener is clicked
11-08 11:10:57.475 16788-16788/com.stanny.xbtest E/set2: 2-listener is clicked
11-08 11:10:57.866 16788-16788/com.stanny.xbtest E/set2: 2-listener is clicked
3、测试addListener
et_test_addListener.addTextChangedListener(object : TextWatcher {
override fun afterTextChanged(p0: Editable?) {
}
override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
}
override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
if (et_test_addListener.text.length == 2) {
Log.e("add1", "1-listener is changed")
}
}
})
et_test_addListener.addTextChangedListener(object : TextWatcher {
override fun afterTextChanged(p0: Editable?) {
}
override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
}
override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
if (et_test_addListener.text.length == 2) {
Log.e("add2", "2-listener is changed")
}
}
})11-08 11:14:49.050 21397-21397/com.stanny.xbtest E/add1: 1-listener is changed
11-08 11:14:49.050 21397-21397/com.stanny.xbtest E/add2: 2-listener is changed可以看到，两个监听，都被打印了。
4、进一步测试addListener
et_test_addListener.addTextChangedListener(object : TextWatcher {
override fun afterTextChanged(p0: Editable?) {
}
override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
}
override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
if (et_test_addListener.text.length == 2) {
finish()//修改位置
}
}
})
et_test_addListener.addTextChangedListener(object : TextWatcher {
override fun afterTextChanged(p0: Editable?) {
}
override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
}
override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
if (et_test_addListener.text.length == 2) {
Log.e("add2", "2-listener is changed")
}
}
})11-08 11:30:48.601 6465-6636/com.stanny.xbtest E/add2: 2-listener is changed那么，你可能会说了，因为这两个是同时发生的，所以才会出现仍然会执行。好，我们继续
5、再进一步测试
et_test_addListener.addTextChangedListener(object : TextWatcher {
override fun afterTextChanged(p0: Editable?) {
}
override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
}
override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
if (et_test_addListener.text.length == 2) {
finish()
}
}
})
et_test_addListener.addTextChangedListener(object : TextWatcher {
override fun afterTextChanged(p0: Editable?) {
}
override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
}
override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
if (et_test_addListener.text.length == 2) {
var timer = Timer()//修改位置
timer.schedule(object : TimerTask() {
override fun run() {
Log.e("add2", "2-listener is changed")
}
}, 1000)
}
}
})我们给第二个监听的打印，一个等待时间，而这时候，该activity已经被finish了
11-08 11:36:02.633 11617-11855/com.stanny.xbtest E/add2: 2-listener is changed也是会执行的，我们的手机上，明明此时activity已经返回了上一级，但是log仍然打印出来了。
那还有没有什么问题？
有的，因为我们现在只是简单的打印了文字，和当前的activity的数据或者控件都没有联系，所以，会不会是这个原因呢？
6、最后一步测试
et_test_addListener.addTextChangedListener(object : TextWatcher {
override fun afterTextChanged(p0: Editable?) {
}
override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
}
override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
if (et_test_addListener.text.length == 2) {
finish()
}
}
})
et_test_addListener.addTextChangedListener(object : TextWatcher {
override fun afterTextChanged(p0: Editable?) {
}
override fun beforeTextChanged(s: CharSequence?, start: Int, count: Int, after: Int) {
}
override fun onTextChanged(s: CharSequence?, start: Int, before: Int, count: Int) {
if (et_test_addListener.text.length == 2) {
var timer = Timer()
timer.schedule(object : TimerTask() {
override fun run() {
Log.e("add2", "2-listener is changed")
btn_test_setListener.setText("123")//修改位置
}
}, 1000)
}
}
})之前我们怀疑因为没涉及到控件，所以不会报错，这次，我们测试在activity被finish掉之后，对控件进行操作。
因为已经finish了，我们也看不到按钮是否改变了文字，但是，我可以确定，没有产生崩溃，没有报错信息。
那么，我们想知道，这个activity真的已经被finish掉了么？还是说，要等到添加的监听都实现完了才会被finish。
这个问题，等有时间，我再来研究。