ViewGroup getChildDrawingOrder与焦点Focus放大遮挡

做AndroidTV项目时，通常都会要实现如下图的功能，某个控件获取焦点后放大，并且显示在最上层。

可以通过getChildDrawingOrder方法实现。



代码如下

RecyclerView

package com.test.wanglu.ordertest;

import android.content.Context;
import android.graphics.Canvas;
import android.support.annotation.Nullable;
import android.support.v7.widget.RecyclerView;
import android.util.AttributeSet;

public class ScaleRecyclerView extends RecyclerView
{
private int mSelectedPosition=0;

public ScaleRecyclerView(Context context) {
super(context);
init();
}

public ScaleRecyclerView(Context context, @Nullable AttributeSet attrs) {
super(context, attrs);
init();
}

public ScaleRecyclerView(Context context, @Nullable AttributeSet attrs, int defStyle) {
super(context, attrs, defStyle);
init();
}

private void init() {
//启用子视图排序功能
setChildrenDrawingOrderEnabled(true);
}

@Override
public void onDraw(Canvas c) {
mSelectedPosition = getChildAdapterPosition(getFocusedChild());
super.onDraw(c);
}

@Override
protected int getChildDrawingOrder(int childCount, int i) {
int position = mSelectedPosition;
if (position < 0) {
return i;
} else {
if (i == childCount - 1) {
if (position > i) {
position = i;
}
return position;
}
if (i == position) {
return childCount - 1;
}
}
return i;
}
}

Activity

package com.test.wanglu.ordertest;

import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.support.v7.widget.GridLayoutManager;
import android.support.v7.widget.LinearLayoutManager;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;

import java.util.List;

/**
* Created by l.wang(516066490@qq.com) on 2017/8/25.
*/
public class MainActivity extends AppCompatActivity
{

private ScaleRecyclerView rv;

@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_main);
rv = findViewById(R.id.rv);
rv.setLayoutManager(new GridLayoutManager(this,3, LinearLayoutManager.VERTICAL,false));
rv.setAdapter(new CommonRVAdapter<String>()
{
@Override
public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent, int viewType) {
View v = LayoutInflater.from(MainActivity.this).inflate(R.layout.item_subnav, parent, false);
return new RecyclerView.ViewHolder(v)
{
};
}

@Override
public void onBindViewHolder(final RecyclerView.ViewHolder holder, int position) {
ImageView iv =holder.itemView.findViewById(R.id.iv);
iv.setOnFocusChangeListener(new View.OnFocusChangeListener()
{
@Override
public void onFocusChange(View view, boolean b) {
rv.invalidate();//这句不能少
if(b){
view.animate().scaleX(1.2f).scaleY(1.2f).setDuration(300).start();
}else {
view.animate().scaleX(1).scaleY(1).setDuration(300).start();
}
}
});
}

@Override
public int getItemCount() {
return 10;
}
});
}

public  abstract class CommonRVAdapter<T> extends RecyclerView.Adapter
{
private List<T> data;

public CommonRVAdapter() {
}

public CommonRVAdapter(List<T> data) {
this.data = data;
}

@Override
public int getItemCount() {
return data == null ? 0 : data.size();
}

public List<T> getData() {
return data;
}

public void setData(List<T> data) {
this.data = data;
}
}
}

activity_main.xml

<?xml version="1.0" encoding="utf-8"?>
<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"
tools:context="com.test.wanglu.ordertest.MainActivity">

<com.test.wanglu.ordertest.ScaleRecyclerView
android:id="@+id/rv"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:clipChildren="false"
android:clipToPadding="false"
android:descendantFocusability="afterDescendants"
/>
</LinearLayout>

android:descendantFocusability=”afterDescendants”不能少,childView优先获取焦点

item_subnav.xml

<?xml version="1.0" encoding="utf-8"?>
<ImageView
android:id="@+id/iv"
xmlns:android="http://schemas.android.com/apk/res/android"
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:adjustViewBounds="true"
android:focusable="true"
android:focusableInTouchMode="true"
android:clickable="true"
android:src="@drawable/menu_date"/>

因为imageview默认不能获取焦点，我用的手机测试的，所以加上

android:focusable=”true”

android:focusableInTouchMode=”true”

这2句，

android:clickable=”true”也不能少，不然手机测试时，点击无法获取焦点