Android 自定义View（自定义控件）

一、创建一个控件类间接或者直接继承View类

二、创建自定义的样式属性放在attr.xml文件里面，如

<?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>

三、在控件类里面实现相关的逻辑

1、重载三个构造方法

public CustomTitleView(Context context, AttributeSet attrs)

public CustomTitleView(Context context)

public CustomTitleView(Context context, AttributeSet attrs, int defStyle)

2、在构造方面里面获取样式属性，类似WP里面的控件样式

TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.CustomTitleView, defStyle, 0);

在构造方面里面可以做一些初始化的操作

3、重载onMeasure方法来测量控件，跟wp的逻辑一模一样

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)

4、重载onDraw方法绘制屏幕

protected void onDraw(Canvas canvas)

canvas是控件的画布对象，在这里你可以在canvas上面绘制或者添加你需要在控件上面显示的内容或者其他的控件。

四、在layout上面使用

1、使用属性的时候需要添加空间的引用

xmlns:custom="http://schemas.android.com/apk/res/com.example.asdlon.customviewdemo"

2、添加控件

    <com.example.asdlon.customviewdemo.CustomTitleView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        custom:titleText="3712"
        android:padding="10dp"
        custom:titleTextColor="#ff0000"
        android:layout_centerInParent="true"
        custom:titleTextSize="40sp" />

import java.util.HashSet;
import java.util.Random;
import java.util.Set;

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.util.TypedValue;
import android.view.View;

public class CustomTitleView extends View
{
    /**
     * 文本
     */
    private String mTitleText;
    /**
     * 文本的颜色
     */
    private int mTitleTextColor;
    /**
     * 文本的大小
     */
    private int mTitleTextSize;

    /**
     * 绘制时控制文本绘制的范围
     */
    private Rect mBound;
    private Paint mPaint;

    public CustomTitleView(Context context, AttributeSet attrs)
    {
        this(context, attrs, 0);
    }

    public CustomTitleView(Context context)
    {
        this(context, null);
    }

    /**
     * 获得我自定义的样式属性
     *
     * @param context
     * @param attrs
     * @param defStyle
     */
    public CustomTitleView(Context context, AttributeSet attrs, int defStyle)
    {
        super(context, attrs, defStyle);
        /**
         * 获得我们所定义的自定义样式属性
         */
        TypedArray a = context.getTheme().obtainStyledAttributes(attrs, R.styleable.CustomTitleView, defStyle, 0);
        int n = a.getIndexCount();
        for (int i = 0; i < n; i++)
        {
            int attr = a.getIndex(i);
            switch (attr)
            {
                case R.styleable.CustomTitleView_titleText:
                    mTitleText = a.getString(attr);
                    break;
                case R.styleable.CustomTitleView_titleTextColor:
                    // 默认颜色设置为黑色
                    mTitleTextColor = a.getColor(attr, Color.BLACK);
                    break;
                case R.styleable.CustomTitleView_titleTextSize:
                    // 默认设置为16sp，TypeValue也可以把sp转化为px
                    mTitleTextSize = a.getDimensionPixelSize(attr, (int) TypedValue.applyDimension(
                            TypedValue.COMPLEX_UNIT_SP, 16, getResources().getDisplayMetrics()));
                    break;

            }

        }
        a.recycle();

        /**
         * 获得绘制文本的宽和高
         */
        mPaint = new Paint();
        mPaint.setTextSize(mTitleTextSize);
        // mPaint.setColor(mTitleTextColor);
        mBound = new Rect();
        mPaint.getTextBounds(mTitleText, 0, mTitleText.length(), mBound);

        this.setOnClickListener(new OnClickListener()
        {

            @Override
            public void onClick(View v)
            {
                mTitleText = randomText();
                postInvalidate();
            }

        });

    }
    private String randomText()
    {
        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);
        }

        return sb.toString();
    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec)
    {
        // super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int width = 0;
        int height = 0;

        /**
         * 设置宽度
         */
        int specMode = MeasureSpec.getMode(widthMeasureSpec);
        int specSize = MeasureSpec.getSize(widthMeasureSpec);
        switch (specMode)
        {
            case MeasureSpec.EXACTLY:// 明确指定了
                width = getPaddingLeft() + getPaddingRight() + specSize;
                break;
            case MeasureSpec.AT_MOST:// 一般为WARP_CONTENT
                width = getPaddingLeft() + getPaddingRight() + mBound.width();
                break;
        }

        /**
         * 设置高度
         */
        specMode = MeasureSpec.getMode(heightMeasureSpec);
        specSize = MeasureSpec.getSize(heightMeasureSpec);
        switch (specMode)
        {
            case MeasureSpec.EXACTLY:// 明确指定了
                height = getPaddingTop() + getPaddingBottom() + specSize;
                break;
            case MeasureSpec.AT_MOST:// 一般为WARP_CONTENT
                height = getPaddingTop() + getPaddingBottom() + mBound.height();
                break;
        }

        setMeasuredDimension(width, height);

    }

    @Override
    protected void onDraw(Canvas canvas)
    {
        mPaint.setColor(Color.YELLOW);
        canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), mPaint);

        mPaint.setColor(mTitleTextColor);
        canvas.drawText(mTitleText, getWidth() / 2 - mBound.width() / 2, getHeight() / 2 + mBound.height() / 2, mPaint);
    }
}

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