Android自定义ViewGroup之CustomGridLayout(一)

时间:2021-05-20

之前写了两篇关于自定义view的文章,本篇讲讲自定义ViewGroup的实现。

我们知道ViewGroup就是View的容器类,我们经常用的LinearLayout,RelativeLayout等都是ViewGroup的子类。并且我们在写布局xml的时候,会告诉容器(凡是以layout为开头的属性,都是为用于告诉容器的),我们的宽度(layout_width)、高度(layout_height)、对齐方式(layout_gravity)等;于是乎,ViewGroup的职能为:给childView计算出建议的宽和高和测量模式 ;决定childView的位置;为什么只是建议的宽和高,而不是直接确定呢,别忘了childView宽和高可以设置为wrap_content,这样只有childView才能计算出自己的宽和高。

View的根据ViewGroup传入的测量值和模式,对自己宽高进行确定(onMeasure中完成),然后在onDraw中完成对自己的绘制。ViewGroup需要给View传入view的测量值和模式(onMeasure中完成),而且对于此ViewGroup的父布局,自己也需要在onMeasure中完成对自己宽和高的确定。此外,需要在onLayout中完成对其childView的位置的指定。

因为ViewGroup有很多子View,所以它的整个绘制过程相对于View会复杂一点,但是还是遵循三个步骤measure,layout,draw,我们依次说明。
本文我们来写一个类似于GridView的网格容器吧,姑且叫做CustomGridView。

自定义属性/获取属性值

<?xml version="1.0" encoding="utf-8"?><resources> <declare-styleable name="CustomGridView"> <attr name="numColumns" format="integer" /> <attr name="hSpace" format="integer" /> <attr name="vSpace" format="integer" /> </declare-styleable></resources> public CustomGridView(Context context, AttributeSet attrs, int defStyle) { super(context, attrs, defStyle); if (attrs != null) { TypedArray a = getContext().obtainStyledAttributes(attrs, R.styleable.CustomGridView); colums = a.getInteger(R.styleable.CustomGridLayout_numColumns, 3); hSpace = a.getInteger(R.styleable.CustomGridLayout_hSpace, 10); vSpace = a.getInteger(R.styleable.CustomGridLayout_vSpace, 10); a.recycle(); } } public MyGridLayout(Context context, AttributeSet attrs) { this(context, attrs, 0); } public MyGridLayout(Context context) { this(context, null); }

LayoutParams

ViewGroup还有一个很重要的知识LayoutParams,LayoutParams存储了子View在加入ViewGroup中时的一些参数信息,在继承ViewGroup类时,一般也需要新建一个新的LayoutParams类,就像SDK中我们熟悉的LinearLayout.LayoutParams,RelativeLayout.LayoutParams类等一样,那么可以这样做,在你定义的ViewGroup子类中,新建一个LayoutParams类继承与ViewGroup.LayoutParams。

public static class LayoutParams extends ViewGroup.LayoutParams { public int left = 0; public int top = 0; public LayoutParams(Context arg0, AttributeSet arg1) { super(arg0, arg1); } public LayoutParams(int arg0, int arg1) { super(arg0, arg1); } public LayoutParams(android.view.ViewGroup.LayoutParams arg0) { super(arg0); } }

那么现在新的LayoutParams类已经有了,如何让我们自定义的ViewGroup使用我们自定义的LayoutParams类来添加子View呢,ViewGroup同样提供了下面这几个方法供我们重写,我们重写返回我们自定义的LayoutParams对象即可。

@Override public ViewGroup.LayoutParams generateLayoutParams(AttributeSet attrs) { return new CustomGridLayout.LayoutParams(getContext(), attrs); } @Override protected ViewGroup.LayoutParams generateDefaultLayoutParams() { return new LayoutParams(LayoutParams.WRAP_CONTENT, LayoutParams.WRAP_CONTENT); } @Override protected ViewGroup.LayoutParams generateLayoutParams(ViewGroup.LayoutParams p) { return new LayoutParams(p); } @Override protected boolean checkLayoutParams(ViewGroup.LayoutParams p) { return p instanceof CustomGridLayout.LayoutParams; }

measure
在onMeasure中需要做两件事:
•计算childView的测量值以及模式
measureChildren(widthMeasureSpec, heightMeasureSpec);
measureChild(child, widthMeasureSpec, heightMeasureSpec);
child.measure(WidthMeasureSpec, HeightMeasureSpec);
•设置ViewGroup自己的宽和高
测量ViewGroup的大小,如果layout_width和layout_height是match_parent或具体的xxxdp,就很简答了,直接调用setMeasuredDimension()方法,设置ViewGroup的宽高即可,如果是wrap_content,就比较麻烦了,我们需要遍历所有的子View,然后对每个子View进行测量,然后根据子View的排列规则,计算出最终ViewGroup的大小。
注意:在自定义View第一篇讲SpecMode时,曾说到UNSPECIFIED一般都是父控件是AdapterView,通过measure方法传入的模式。在这里恰好就用到了。

@Override protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { int widthMode = MeasureSpec.getMode(widthMeasureSpec); int heightMode = MeasureSpec.getMode(heightMeasureSpec); int sizeWidth = MeasureSpec.getSize(widthMeasureSpec); int sizeHeight = MeasureSpec.getSize(heightMeasureSpec); //UNSPECIFIED一般都是父控件是AdapterView,通过measure方法传入的模式 final int childWidthMeasureSpec = MeasureSpec.makeMeasureSpec(sizeWidth, MeasureSpec.UNSPECIFIED); final int childHeightMeasureSpec = MeasureSpec.makeMeasureSpec(sizeHeight, MeasureSpec.UNSPECIFIED); measureChildren(childWidthMeasureSpec, childHeightMeasureSpec); int childCount = this.getChildCount(); int line = childCount % colums == 0 ? childCount / colums : (childCount + colums) / colums; //宽布局为wrap_content时,childWidth取childView宽的最大值,否则动态计算 if (widthMode == MeasureSpec.AT_MOST) { for (int i = 0; i < childCount; i++) { View child = this.getChildAt(i); childWidth = Math.max(childWidth, child.getMeasuredWidth()); } } else if (widthMode == MeasureSpec.EXACTLY) { childWidth = (sizeWidth - (colums - 1) * hSpace) / colums; } //高布局为wrap_content时,childHeight取childView高的最大值,否则动态计算 if (heightMode == MeasureSpec.AT_MOST) { for (int i = 0; i < childCount; i++) { View child = this.getChildAt(i); childHeight = Math.max(childHeight, child.getMeasuredHeight()); } } else if (heightMode == MeasureSpec.EXACTLY) { childHeight = (sizeHeight - (line - 1) * vSpace) / line; } //遍历每个子view,将它们左上角坐标保存在它们的LayoutParams中,为后面onLayout服务 for (int i = 0; i < childCount; i++) { View child = this.getChildAt(i); LayoutParams lParams = (LayoutParams) child.getLayoutParams(); lParams.left = (i % colums) * (childWidth + hSpace); lParams.top = (i / colums) * (childHeight + vSpace); } //当宽高为wrap_content时,分别计算出的viewGroup宽高 int wrapWidth; int wrapHeight; if (childCount < colums) { wrapWidth = childCount * childWidth + (childCount - 1) * hSpace; } else { wrapWidth = colums * childWidth + (colums - 1) * hSpace; } wrapHeight = line * childHeight + (line - 1) * vSpace; setMeasuredDimension(widthMode == MeasureSpec.AT_MOST? wrapWidth:sizeWidth,heightMode == MeasureSpec.AT_MOST? wrapHeight:sizeHeight); }

layout
最核心的就是调用layout方法,根据我们measure阶段获得的LayoutParams中的left和top字段,也很好对每个子View进行位置排列。

@Override protected void onLayout(boolean changed, int l, int t, int r, int b) { int childCount = this.getChildCount(); for (int i = 0; i < childCount; i++) { View child = this.getChildAt(i); LayoutParams lParams = (LayoutParams) child.getLayoutParams(); child.layout(lParams.left, lParams.top, lParams.left + childWidth, lParams.top + childHeight); } }

draw
ViewGroup在draw阶段,其实就是按照子类的排列顺序,调用子类的onDraw方法,因为我们只是View的容器,本身一般不需要draw额外的修饰,所以往往在onDraw方法里面,只需要调用ViewGroup的onDraw默认实现方法即可。不需要重写。

最后,在自定义ViewGroup中定义GridAdatper接口,以便在外部可以为ViewGroup设置适配器。

public interface GridAdatper { View getView(int index); int getCount(); } /** 设置适配器 */ public void setGridAdapter(GridAdatper adapter) { this.adapter = adapter; // 动态添加视图 int size = adapter.getCount(); for (int i = 0; i < size; i++) { addView(adapter.getView(i)); } }

并且在自定义ViewGroup中定义OnItemClickListener接口,以便在外部可以获取到childView的点击事件。

public interface OnItemClickListener { void onItemClick(View v, int index); } public void setOnItemClickListener(final OnItemClickListener listener) { if (this.adapter == null) return; for (int i = 0; i < adapter.getCount(); i++) { final int index = i; View view = getChildAt(i); view.setOnClickListener(new OnClickListener() { @Override public void onClick(View v) { listener.onItemClick(v, index); } }); } }

使用自定义的CustomViewGroup

布局文件:

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res/com.hx.customgridview" android:layout_width="match_parent" android:layout_height="match_parent" android:background="#303030" android:orientation="vertical" > <com.hx.customgridview.CustomGridLayout android:id="@+id/gridview" android:layout_width="200dp" android:layout_height="300dp" android:background="#1e1d1d" app:hSpace="10" app:vSpace="10" app:numColumns="3"/></LinearLayout>

grid_item:

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent" android:gravity="center" android:orientation="vertical" > <ImageView android:id="@+id/iv" android:layout_width="match_parent" android:layout_height="match_parent" android:scaleType="fitXY"/></LinearLayout>

Java文件:

protected void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); grid = (CustomGridLayout) findViewById(R.id.gridview); grid.setGridAdapter(new GridAdatper() { @Override public View getView(int index) { View view = getLayoutInflater().inflate(R.layout.grid_item, null); ImageView iv = (ImageView) view.findViewById(R.id.iv); iv.setImageResource(srcs[index]); return view; } @Override public int getCount() { return srcs.length; } }); grid.setOnItemClickListener(new OnItemClickListener() { @Override public void onItemClick(View v, int index) { Toast.makeText(MainActivity.this, "item="+index, Toast.LENGTH_SHORT).show(); } }); }}

运行后效果图如下:

改变一下布局:

<com.hx.customgridview.CustomGridLayout android:id="@+id/gridview" android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="#1e1d1d" app:hSpace="10" app:vSpace="10" app:numColumns="3"/>

再改变

<com.hx.customgridview.CustomGridLayout android:id="@+id/gridview" android:layout_width="match_parent" android:layout_height="match_parent" android:background="#1e1d1d" app:hSpace="10" app:vSpace="10" app:numColumns="3"/>

再变

<com.hx.customgridview.CustomGridLayout android:id="@+id/gridview" android:layout_width="wrap_content" android:layout_height="wrap_content" android:background="#1e1d1d" app:hSpace="10" app:vSpace="10" app:numColumns="4"/>

Demo下载地址:http://xiazai.jb51.net/201609/yuanma/CustomGridLayout(jb51.net).rar

以上就是本文的全部内容,希望对大家的学习有所帮助,也希望大家多多支持。

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