自定义View（1）

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步骤

自定义属性
重写ondraw（）
重写onMeasure（）

带着问题看代码

在不重写onMeasure方法时， wrap_content与match_parent对布局影响的区别
测量之前怎么去获取View的大小
setMeasuredDimension（…）方法的作用

效果图

这里写图片描述

自定义属性

布局文件

<?xml version="1.0" encoding="utf-8"?><RelativeLayout    xmlns:android="http://schemas.android.com/apk/res/android"    xmlns:test="http://schemas.android.com/apk/res-auto"    xmlns:tools="http://schemas.android.com/tools"    android:id="@+id/activity_main"    android:layout_width="match_parent"    android:layout_height="match_parent"    tools:context="simplifyreader.nobita.com.customview.MainActivity">    <simplifyreader.nobita.com.customview.MyView        android:layout_width="wrap_content"        android:layout_height="wrap_content"        android:layout_centerInParent="true"        test:backColor="#ff0"        test:text="这里"        test:textColor="#f00"        test:textSize="50sp"/></RelativeLayout>

分析：

1、添加xmlns:test=”http://schemas.android.com/apk/res-auto”，其实test为自定义属性前缀

attrs文件

在values文件目录下创建attrs.xml文件

<resources>    <declare-styleable name="MyView">        <attr name="textColor" format="color"/>        <attr name="text" format="string"/>        <attr name="backColor" format="color"/>        <attr name="textSize" format="dimension"/>    </declare-styleable></resources>

自定义View代码

在代码中有关键注释

public class MyView extends View {    Paint mPaint;    Paint mBackPaint;    String mText;    int mTextColor;    float mTextSize;    int defalutTextColor = Color.RED;    float defalutTextSize = Color.RED;    int mBackColor;    int defalutBackColor = Color.BLACK;    private Rect mBound;    public MyView(Context context) {        super(context);    }    public MyView(Context context, AttributeSet attrs) {        super(context, attrs);        mPaint = new Paint();        mBackPaint = new Paint();        //获取xml文件中自定义属性集合        TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.MyView);        mText = a.getString(R.styleable.MyView_text);        mTextColor = a.getColor(R.styleable.MyView_textColor, defalutTextColor);        mBackColor = a.getColor(R.styleable.MyView_backColor, defalutBackColor);        mTextSize = a.getDimension(R.styleable.MyView_textSize, 36);        a.recycle();        mPaint.setColor(mTextColor);        mPaint.setTextSize(mTextSize);        mBackPaint.setColor(mBackColor);        //获取mText的长宽，并封装进mBound        mBound = new Rect();        mPaint.getTextBounds(mText, 0, mText.length(), mBound);    }    @Override    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {        int widthMode = MeasureSpec.getMode(widthMeasureSpec);        int heightMode = MeasureSpec.getMode(heightMeasureSpec);        int widthSize = MeasureSpec.getSize(widthMeasureSpec);        int heightSize = MeasureSpec.getSize(heightMeasureSpec);        int width;        int height;        if (widthMode == MeasureSpec.EXACTLY) {            width = widthSize;        } else {            width = mBound.width() + getPaddingLeft() + getPaddingRight();        }        if (heightMode == MeasureSpec.EXACTLY) {            height = heightSize;        } else {            height = mBound.height() + getPaddingBottom() + getPaddingTop();        }        //必须调用，设置该View的长宽        setMeasuredDimension(width, height);    }    @Override    protected void onDraw(Canvas canvas) {        super.onDraw(canvas);        //绘制背景        canvas.drawRect(0, 0, getMeasuredWidth(), getMeasuredHeight(), mBackPaint);        //绘制文本,第二个和第三个参数为x_y坐标（文本的左下角）        canvas.drawText(mText, getWidth() / 2 - mBound.width() / 2, getHeight() / 2 + mBound.height() / 2, mPaint);    }}

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