Android setFocusableInTouchMode 方法使用和源码详解

是什么

一般点击一个button，就会执行onclick 事件，但是有些情况，我们想要点击button之后，先获取焦点，然后再次点击一次，才执行onClick 事件。这时候，setFocusableInTouchMode 就派上用场了。

实践出真知：

布局文件：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"xmlns:tools="http://schemas.android.com/tools"android:layout_width="match_parent"android:layout_height="match_parent"tools:context="com.example.fragment.FocusableInTouchModeFragment"android:orientation="vertical"><Buttonandroid:layout_width="match_parent"android:layout_height="50dp"android:text="bt1"android:id="@+id/bt1"/><Buttonandroid:layout_width="match_parent"android:layout_height="50dp"android:text="bt2"android:id="@+id/bt2"/></LinearLayout>

代码1：只给bt1 设置setFocusableInTouchMode

        bt1.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Log.d(TAG, "onClick: " + bt1);}});bt1.setOnFocusChangeListener(new View.OnFocusChangeListener() {@Overridepublic void onFocusChange(View v, boolean hasFocus) {Log.d(TAG, "onFocusChange: " + bt1);}});bt1.setFocusableInTouchMode(true);bt2.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Log.d(TAG, "onClick: " + bt2);}});bt2.setOnFocusChangeListener(new View.OnFocusChangeListener() {@Overridepublic void onFocusChange(View v, boolean hasFocus) {Log.d(TAG, "onFocusChange: " + bt2);}});

我们看下打印：

2021-03-29 20:24:39.201 9863-9863/com.pipiyang.cn03 D/FocusableInTouchModeFra: onFocusChange: androidx.appcompat.widget.AppCompatButton{2988e98 VFED..C.. .F.P..ID 0,0-1440,175 #7f080091 app:id/bt1}
2021-03-29 20:24:45.872 9863-9863/com.pipiyang.cn03 D/FocusableInTouchModeFra: onClick: androidx.appcompat.widget.AppCompatButton{f5b73f3 VFED..C.. ...P.... 0,175-1440,350 #7f080092 app:id/bt2}
2021-03-29 20:24:52.783 9863-9863/com.pipiyang.cn03 D/FocusableInTouchModeFra: onClick: androidx.appcompat.widget.AppCompatButton{2988e98 VFED..C.. .F.P.... 0,0-1440,175 #7f080091 app:id/bt1}

bt1 因为设置了setFocusableInTouchMode，第一次点击会获取焦点，第二次点击才会触发onClick，而bt2 直接响应了onClick.

代码2：两个bt都设置setFocusableInTouchMode

        bt1.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Log.d(TAG, "onClick: " + bt1);}});bt1.setOnFocusChangeListener(new View.OnFocusChangeListener() {@Overridepublic void onFocusChange(View v, boolean hasFocus) {Log.d(TAG, "onFocusChange: " + bt1);}});bt1.setFocusableInTouchMode(true);bt2.setOnClickListener(new View.OnClickListener() {@Overridepublic void onClick(View v) {Log.d(TAG, "onClick: " + bt2);}});bt2.setFocusableInTouchMode(true);bt2.setOnFocusChangeListener(new View.OnFocusChangeListener() {@Overridepublic void onFocusChange(View v, boolean hasFocus) {Log.d(TAG, "onFocusChange: " + bt2);}});

2021-03-29 20:26:36.830 10074-10074/com.pipiyang.cn03 D/FocusableInTouchModeFra: onFocusChange: androidx.appcompat.widget.AppCompatButton{65c8907 VFED..C.. .F.P..ID 0,175-1440,350 #7f080092 app:id/bt2}
2021-03-29 20:26:39.886 10074-10074/com.pipiyang.cn03 D/FocusableInTouchModeFra: onFocusChange: androidx.appcompat.widget.AppCompatButton{65c8907 VFED..C.. ......ID 0,175-1440,350 #7f080092 app:id/bt2}
2021-03-29 20:26:39.886 10074-10074/com.pipiyang.cn03 D/FocusableInTouchModeFra: onFocusChange: androidx.appcompat.widget.AppCompatButton{a5c551e VFED..C.. .F.P..ID 0,0-1440,175 #7f080091 app:id/bt1}
2021-03-29 20:26:49.648 10074-10074/com.pipiyang.cn03 D/FocusableInTouchModeFra: onFocusChange: androidx.appcompat.widget.AppCompatButton{a5c551e VFED..C.. ......ID 0,0-1440,175 #7f080091 app:id/bt1}
2021-03-29 20:26:49.649 10074-10074/com.pipiyang.cn03 D/FocusableInTouchModeFra: onFocusChange: androidx.appcompat.widget.AppCompatButton{65c8907 VFED..C.. .F.P..ID 0,175-1440,350 #7f080092 app:id/bt2}

如果两个都是被设置了setFocusableInTouchMode，那么只有连续两次点击一个button，才会触发onClick,如果你点了另外一个，那么本来点击的button 就会失去焦点。你需要再次点击之前的button 获取焦点，然后再点击一次才会执行onClick。

但是一旦一个view 已经获取了焦点，而且焦点没有发生变化，那么再次点击会直接执行onClick 方法。

怎么实现的？

android.view.View#onTouchEvent

    public boolean onTouchEvent(MotionEvent event) {if (clickable || (viewFlags & TOOLTIP) == TOOLTIP) {switch (action) {case MotionEvent.ACTION_UP:mPrivateFlags3 &= ~PFLAG3_FINGER_DOWN;boolean prepressed = (mPrivateFlags & PFLAG_PREPRESSED) != 0;if ((mPrivateFlags & PFLAG_PRESSED) != 0 || prepressed) {// take focus if we don't have it already and we should in// touch mode.boolean focusTaken = false;//如果是isFocusableInTouchMode 那么就调用requestFocus 方法if (isFocusable() && isFocusableInTouchMode() && !isFocused()) {focusTaken = requestFocus();}if (!mHasPerformedLongPress && !mIgnoreNextUpEvent) {// This is a tap, so remove the longpress checkremoveLongPressCallback();// Only perform take click actions if we were in the pressed state// 如果说获取了焦点 那么就不执行onClick 了if (!focusTaken) {// Use a Runnable and post this rather than calling// performClick directly. This lets other visual state// of the view update before click actions start.if (mPerformClick == null) {mPerformClick = new PerformClick();}if (!post(mPerformClick)) {performClickInternal();}}}             }break;

我们直接看View 的onTouchEvent 方法的ACTION_UP，我们发现如果你设置了setFocusableInTouchMode，并且没有获取到焦点，那么他会首先去获取焦点，不执行onClick。