Android-6步教你自定义View

一时失言乱红尘 2022-07-12 03:53 134阅读 0赞

如果你打算完全定制一个View，那么你需要实现View类（所有的Android View都实现于这个类），并且实现确定尺寸的onMeasure(…))方法和确认绘图的onDraw(…))方法。

\#自定义View一共分为6步

\#第一步

public class SmileyView extends View {
        private Paint mCirclePaint;
        private Paint mEyeAndMouthPaint;
    
        private float mCenterX;
        private float mCenterY;
        private float mRadius;
        private RectF mArcBounds = new RectF();
    
        public SmileyView(Context context) {
            this(context, null);
        }
    
        public SmileyView(Context context, AttributeSet attrs) {
            this(context, attrs, 0);
        }
    
        public SmileyView(Context context, AttributeSet attrs, int defStyleAttr) {
            super(context, attrs, defStyleAttr);
            initPaints();
        }
    
        private void initPaints() {/* ... */}
    
        @Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {/* ... */}
    
        @Override
        protected void onDraw(Canvas canvas) {/* ... */}
    }

\#2.实现画笔paint类

本文一共两只画笔

private void initPaints() {
        mCirclePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mCirclePaint.setStyle(Paint.Style.FILL);
        mCirclePaint.setColor(Color.YELLOW);
        mEyeAndMouthPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mEyeAndMouthPaint.setStyle(Paint.Style.STROKE);
        mEyeAndMouthPaint.setStrokeWidth(16 * getResources().getDisplayMetrics().density);
        mEyeAndMouthPaint.setStrokeCap(Paint.Cap.ROUND);
        mEyeAndMouthPaint.setColor(Color.BLACK);
    }

\#3.覆写onMeasure(…)方法  
实现这个方法告诉了母容器如何放弃自定义View，可以通过提供的measureSpecs来决定你的View的高和宽，以下是一个正方形，确认它的宽和高是一样的。

@Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int w = MeasureSpec.getSize(widthMeasureSpec);
        int h = MeasureSpec.getSize(heightMeasureSpec);
    
        int size = Math.min(w, h);
        setMeasuredDimension(size, size);
    }

\#\#注意：\#\#  
这个方法需要至少保证一个setMeasuredDimension(…)调用，否则会报IllegalStateException错误。

\#4.实现onSizeChanged(…)方法

这个方法是你获取View现在的宽和高. 这里我们计算的是中心和半径。

@Override
    protected void onSizeChanged(int w, int h, int oldw, int oldh) {
        mCenterX = w / 2f;
        mCenterY = h / 2f;
        mRadius = Math.min(w, h) / 2f;
    }

\#5.实现onDraw(…)方法

这个方法提供了如何绘制view，它提供的Canvas类可以进行绘制。

@Override
    protected void onDraw(Canvas canvas) {
        // draw face
        canvas.drawCircle(mCenterX, mCenterY, mRadius, mCirclePaint);
        // draw eyes
        float eyeRadius = mRadius / 5f;
        float eyeOffsetX = mRadius / 3f;
        float eyeOffsetY = mRadius / 3f;
        canvas.drawCircle(mCenterX - eyeOffsetX, mCenterY - eyeOffsetY, eyeRadius, mEyeAndMouthPaint);
        canvas.drawCircle(mCenterX + eyeOffsetX, mCenterY - eyeOffsetY, eyeRadius, mEyeAndMouthPaint);
        // draw mouth
        float mouthInset = mRadius /3f;
        mArcBounds.set(mouthInset, mouthInset, mRadius * 2 - mouthInset, mRadius * 2 - mouthInset);
        canvas.drawArc(mArcBounds, 45f, 90f, false, mEyeAndMouthPaint);
    }

\#6.添加你的View

\#\#到此就结束了，自定义View没你想的那么难\#\#