所有的view控件有一个findFocus方法,这个方法如下
/** * Find the view in the hierarchy rooted at this view that currently has * focus. * * @return The view that currently has focus, or null if no focused view can * be found. */ public View findFocus() { return (mPrivateFlags & PFLAG_FOCUSED) != 0 ? this : null; }
大概意思就是,获得当前试图下,拥有焦点的控件
我们可以验证下它的具体使用
看demo
xml
<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" android:orientation="vertical" android:padding="20dp" tools:context="com.example.testcode.MainActivity" > <TextView android:id="@+id/tv" android:layout_width="match_parent" android:layout_height="200dp" android:layout_marginBottom="10dp" android:clickable="true" android:focusable="true" android:textSize="30sp" android:focusableInTouchMode="true" android:background="@drawable/select" android:textColor="#ffffff" /> <LinearLayout android:id="@+id/aaa" android:layout_width="match_parent" android:layout_height="0dp" android:layout_marginBottom="10dp" android:layout_weight="1" android:orientation="horizontal" > <Button android:id="@+id/bt_1" android:layout_width="60dp" android:layout_height="60dp" android:layout_marginLeft="5dp" android:background="@drawable/select" android:focusableInTouchMode="true" android:textColor="#ffffff" /> <Button android:id="@+id/bt_2" android:layout_width="60dp" android:layout_height="60dp" android:layout_marginLeft="5dp" android:background="@drawable/select" android:focusableInTouchMode="true" android:textColor="#ffffff" /> <Button android:id="@+id/bt_3" android:layout_width="60dp" android:layout_height="60dp" android:layout_marginLeft="5dp" android:background="@drawable/select" android:focusableInTouchMode="true" android:textColor="#ffffff" /> <Button android:id="@+id/bt_4" android:layout_width="60dp" android:layout_height="60dp" android:layout_marginLeft="5dp" android:background="@drawable/select" android:focusableInTouchMode="true" android:textColor="#ffffff" /> </LinearLayout> <Button android:id="@+id/bt" android:layout_width="100dp" android:layout_height="100dp" android:background="@drawable/select" /> </LinearLayout>
activity
package com.example.testcode; import com.example.testcode.R.id; import android.app.Activity; import android.content.Intent; import android.os.Bundle; import android.view.Menu; import android.view.MenuItem; import android.view.View; import android.view.View.OnClickListener; import android.widget.Button; import android.widget.LinearLayout; import android.widget.TextView; public class MainActivity extends Activity { private TextView textView; private Button button; private LinearLayout relativeLayout; @Override protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); textView = (TextView) findViewById(R.id.tv); button = (Button)findViewById(R.id.bt); relativeLayout = (LinearLayout)findViewById(R.id.aaa); textView.setText("当前焦点所在view"); button.setText("显示当前focus"); button.setOnClickListener(new OnClickListener() { @Override public void onClick(View arg0) { // TODO Auto-generated method stub View view = relativeLayout.findFocus(); textView.setText(""+view); } }); } @Override public boolean onCreateOptionsMenu(Menu menu) { // Inflate the menu; this adds items to the action bar if it is present. getMenuInflater().inflate(R.menu.main, menu); return true; } @Override public boolean onOptionsItemSelected(MenuItem item) { // Handle action bar item clicks here. The action bar will // automatically handle clicks on the Home/Up button, so long // as you specify a parent activity in AndroidManifest.xml. int id = item.getItemId(); if (id == R.id.action_settings) { return true; } return super.onOptionsItemSelected(item); } }
我们看下它的效果
从上面的结果,我们可以得出结论
1.这个方法其实加在viewGroup上比较有作用,它得到的是当前拥有焦点的子控件view
2.如果焦点不在这个控件内的话,返回的是一个null
3.如果你把这个方法加在ListView上的话,返回的是它的item
另外,我们还发现了另外一个跟focus相关的方法,如下
/** * Find the nearest view in the specified direction that can take focus. * This does not actually give focus to that view. * * @param direction One of FOCUS_UP, FOCUS_DOWN, FOCUS_LEFT, and FOCUS_RIGHT * * @return The nearest focusable in the specified direction, or null if none * can be found. */ public View focusSearch(@FocusRealDirection int direction) { if (mParent != null) { return mParent.focusSearch(this, direction); } else { return null; } }
这个方法,其实是代码获得某个控件获得焦点以后,下一个焦点移动到的控件。如果我们没有对这个控件的焦点进行操作,它就遵循android本身的焦点顺序。如果我们进行了操作,例如
<Button android:id="@+id/bt_3" android:layout_width="60dp" android:layout_height="60dp" android:layout_marginLeft="5dp" android:background="@drawable/select" android:focusableInTouchMode="true" android:nextFocusRight="@+id/tv" android:textColor="#ffffff" />
增加了nextfocus 属性,我们得到的其实就是这个里面焦点跳转view