1.自定义view入门

1.继承自view

系统提供的view 如 TextView 、ImageView 都是继承自view的；

2.自定义一个TextView

通过自定义一个TextView 来熟悉继承自view 的自定义view的api用法

3.onMeasure

用来处理控件的大小

 	@Override

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

    }

//获取宽高的模式

int widthMode = MeasureSpec.getMode(widthMeasureSpec);

int heightMode = MeasureSpec.getMode(heightMeasureSpec);    

//mode

//MeasureSpec.AT_MOST 指定了wrap_content

//MeasureSpec.EXACTLY 指定了确切的值 match_parent fill_parent

//MeasureSpec.UNSPECIFIED 尽可能的大

4.onDraw

用于绘制

   @Override

    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);

//        canvas.drawText();

    }

5.onTouchEvent

用于处理用户触摸事件

    @Override

    public boolean onTouchEvent(MotionEvent event) {

        switch (event.getAction()) {

            case MotionEvent.ACTION_DOWN:

                break;

            case MotionEvent.ACTION_MOVE:

                break;

            case MotionEvent.ACTION_UP:

                break;

        }

        return super.onTouchEvent(event);

    }

6.自定义属性

用来配置自定义控件的属性

<?xml version="1.0" encoding="utf-8"?>

<resources>

    <!--    自定义控件的名称 name="TextView"-->

    <declare-styleable name="TextView">

        <attr name="text" format="string" />

        <attr name="textColor" format="color" />

        <attr name="textSize" format="dimension" />

        <attr name="maxLength" format="integer" />

        <attr name="background" format="reference|color" />

        <!--枚举-->

        <attr name="inputType" format="enum">

            <enum name="number" value="1" />

            <enum name="text" value="2" />

            <enum name="password" value="3" />

        </attr>

    </declare-styleable>

</resources>

在布局中使用

<com.nb.customview.TextView

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    app:text="张三"

    app:textColor="@color/purple_500"

    app:textSize="16" />

在自定义控件中获取

    public TextView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {

        super(context, attrs, defStyleAttr);

        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.TextView);

        mText = typedArray.getString(R.styleable.TextView_text);

        mTextSize = typedArray.getDimensionPixelSize(R.styleable.TextView_textSize, mTextSize);

        mTextColor = typedArray.getColor(R.styleable.TextView_textColor, mTextColor);

        typedArray.recycle();

    }

7.完整的代码

package com.nb.customview;

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.Log;

import android.util.TypedValue;

import android.view.MotionEvent;

import android.view.View;

import android.widget.LinearLayout;

import androidx.annotation.Nullable;

/**

 * Created by DongKing on 2020/11/5

 * Version 1.0

 * Describe:自定义TextView

 */

class TextView extends View {

    private static final String TAG = "TextView";

    private String mText;

    private int mTextSize = 15;

    private int mTextColor = Color.BLACK;

    private Paint mPaint;

    //    在java 代码中new 的时候使用

    public TextView(Context context) {

        this(context, null);

    }

    //    在layout 中使用

    public TextView(Context context, @Nullable AttributeSet attrs) {

        this(context, attrs, 0);

    }

    //有style时使用

    public TextView(Context context, @Nullable AttributeSet attrs, int defStyleAttr) {

        super(context, attrs, defStyleAttr);

        //获取xml中设置的属性

        TypedArray typedArray = context.obtainStyledAttributes(attrs, R.styleable.TextView);

        mText = typedArray.getString(R.styleable.TextView_nbText);

        mTextSize = typedArray.getDimensionPixelSize(R.styleable.TextView_nbTextSize, sp2px(mTextSize));

        mTextColor = typedArray.getColor(R.styleable.TextView_nbTextColor, mTextColor);

        typedArray.recycle();

        //初始化画笔

        mPaint = new Paint();

        mPaint.setAntiAlias(true);

        mPaint.setTextSize(mTextSize);

        mPaint.setColor(mTextColor);

    }

    private int sp2px(int sp) {

        return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, sp,

                getResources().getDisplayMetrics());

    }

    /**

     * 指定宽高

     * 针对不同的情况

     *

     * @param widthMeasureSpec

     * @param heightMeasureSpec

     */

    @Override

    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {

        super.onMeasure(widthMeasureSpec, heightMeasureSpec);

        int widthMode = MeasureSpec.getMode(widthMeasureSpec);

        int heightMode = MeasureSpec.getMode(heightMeasureSpec);

        //1.如果指定大小

        int width = MeasureSpec.getSize(widthMeasureSpec);

        //2.wrap_content 计算获取值

        if (widthMode == MeasureSpec.AT_MOST) {

            Rect bounds = new Rect();

            mPaint.getTextBounds(mText, 0, mText.length(), bounds);

            width = bounds.width() + getPaddingLeft() + getPaddingRight();

        }

        int height = MeasureSpec.getSize(heightMeasureSpec);

        if (heightMode == MeasureSpec.AT_MOST) {

            Rect bounds = new Rect();

            mPaint.getTextBounds(mText, 0, mText.length(), bounds);

            height = bounds.height() + getPaddingTop() + getPaddingBottom();

        }

        //设置控件的宽高

        setMeasuredDimension(width, height);

    }

    /**

     * 用于绘制

     *

     * @param canvas

     */

    @Override

    protected void onDraw(Canvas canvas) {

        super.onDraw(canvas);

        Paint.FontMetricsInt fontMetrics = mPaint.getFontMetricsInt();

        int dy = (fontMetrics.bottom - fontMetrics.top) / 2 - fontMetrics.bottom;

        int baseLine = getHeight() / 2 + dy;

        canvas.drawText(mText, getPaddingLeft(), baseLine, mPaint);

    }

}

<?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-auto"

    xmlns:tools="http://schemas.android.com/tools"

    android:layout_width="match_parent"

    android:layout_height="match_parent"

    android:orientation="vertical"

    tools:context=".MainActivity">

    <LinearLayout

        android:id="@+id/container"

        android:layout_width="match_parent"

        android:layout_height="match_parent"

        android:orientation="vertical">

        <com.nb.customview.TextView

            android:padding="10dp"

            android:layout_width="wrap_content"

            android:layout_height="wrap_content"

            android:background="@color/purple_200"

            app:nbText="张三"

            app:nbTextColor="@color/teal_200"

            app:nbTextSize="20sp" />

    </LinearLayout>

</LinearLayout>

巴特西

1.自定义view入门

1.继承自view

2.自定义一个TextView

3.onMeasure

4.onDraw

5.onTouchEvent

6.自定义属性

7.完整的代码

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