[AndroidUI]自定义view(一)

参考链接：http://blog.csdn.net/lmj623565791/article/details/24252901

自定义view的步骤：

1.res/values/下新建一个attrs.xml，创建自定义的属性

属性类型可以取：string,color,demension,integer,enum,reference,float,boolean,fraction,flag

2.在布局文件中添加自定义的view，为自定义的属性赋值

自定义的属性属于不同的命名空间

3.为自定义的view重写方法，获取自定义的属性

1.attrs.xml

<?xml version="1.0" encoding="utf-8"?>
<resources>
    <attr name="titleText" format="string" />  
    <attr name="titleTextColor" format="color" />  
    <attr name="titleTextSize" format="dimension" />  
  
    <declare-styleable name="CustomTitleView">  
        <attr name="titleText" />  
        <attr name="titleTextColor" />  
        <attr name="titleTextSize" />  
    </declare-styleable> 
</resources>

2.

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:custom="http://schemas.android.com/apk/res/com.example.testview"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <com.example.testview.MyView 
        android:layout_width="match_parent"
        android:layout_height="100dp"
        custom:titleText="3712"
        custom:titleTextColor="#ff0000ff"  
        custom:titleTextSize="40sp"/>

</LinearLayout>

3.

package com.example.testview;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.widget.TextView;

public class MyView extends TextView{

	private String titleText;
	private int titleTextColor;
	private float titleTextSize;
	
	private Rect rect;//绘制时控制文本绘制的范围
	private Paint paint;
	
	public MyView(Context context) {
		super(context);
	}

	//默认的布局文件调用的是两个参数的构造方法
	public MyView(Context context, AttributeSet attrs) {
		this(context, attrs, 0);
	}

	public MyView(Context context, AttributeSet attrs, int defStyle)
	{
		super(context, attrs, defStyle);
		
		TypedArray typedArray = context.getTheme().
			obtainStyledAttributes(attrs, R.styleable.CustomTitleView, defStyle, 0);
		
		titleText = typedArray.getString(R.styleable.CustomTitleView_titleText);
		titleTextColor = typedArray.getColor(R.styleable.CustomTitleView_titleTextColor, Color.BLACK);
		titleTextSize = typedArray.getDimension(R.styleable.CustomTitleView_titleTextSize, 80);
		
		rect = new Rect();
		paint = new Paint();

		paint.setTextSize(titleTextSize);
		paint.getTextBounds(titleText, 0, titleText.length(), rect);//文本绘制范围
		
		typedArray.recycle();
	}
	
	@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		//即android:layout_width和android:layout_height
		super.onMeasure(widthMeasureSpec, heightMeasureSpec);
	}
	
	@Override
	protected void onDraw(Canvas canvas) {
		//绘制背景
		paint.setColor(Color.YELLOW);
		canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), paint);
		
		paint.setColor(titleTextColor);
		canvas.drawText(titleText, getWidth() / 2 - rect.width() / 2, getHeight() / 2 + rect.height() / 2, paint);
	}
}

当自定义的view设置宽高为一个确定的值，或者为match_parent时，view的宽高是正常的，而如果设置宽高为wrap_content时，往往会达不到预料中的效果。

所以，当设置了wrap_content时，我们需要自己进行测量，即重写onMeasure方法：

重写之前先了解MeasureSpec的specMode,一共三种类型：

EXACTLY：设置了明确的值或者是match_parent

AT_MOST：表示子布局限制在一个最大值内，一般为wrap_content

UNSPECIFIED：表示子布局想要多大就多大，很少使用

下面我们重写onMeasure方法：

@Override
	protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
		int widthMode = MeasureSpec.getMode(widthMeasureSpec);  
	    int widthSize = MeasureSpec.getSize(widthMeasureSpec);  
	    int heightMode = MeasureSpec.getMode(heightMeasureSpec);  
	    int heightSize = MeasureSpec.getSize(heightMeasureSpec);  
	    int width;  
	    int height;
	    
	    if(widthMode == MeasureSpec.EXACTLY)
	    {
	    	width = widthSize;
	    }
	    else
	    {
	    	width = getPaddingLeft() + rect.width() + getPaddingRight();
	    }
	    
	    if(heightMode == MeasureSpec.EXACTLY)
	    {
	    	height = heightSize;
	    }
	    else
	    {
	    	height = getPaddingTop() + rect.height() + getPaddingBottom();
	    }
	    
	    setMeasuredDimension(width, height);
	}

同时，我们可以为自定义的view定义点击事件(在构造函数中添加)：

                this.setOnClickListener(new OnClickListener() {
			
			@Override
			public void onClick(View v) {
				//随机生成一个四位数
				Random random = new Random();  
		        Set<Integer> set = new HashSet<Integer>();  
		        while (set.size() < 4)  
		        {  
		            int randomInt = random.nextInt(10);  
		            set.add(randomInt);  
		        }  
		        StringBuffer sb = new StringBuffer();  
		        for (Integer i : set)  
		        {  
		            sb.append("" + i);  
		        }
				
		        titleText = sb.toString();
		        postInvalidate();
			}
		});

效果图：