如果你打算完全定制一個(gè)View，那么你需要實(shí)現(xiàn)View類(lèi)（所有的Android View都實(shí)現(xiàn)于這個(gè)類(lèi)）错邦，并且實(shí)現(xiàn)確定尺寸的onMeasure(…))方法和確認(rèn)繪圖的onDraw(…))方法。
自定義View一共分為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.實(shí)現(xiàn)畫(huà)筆paint類(lèi)
本文一共兩只畫(huà)筆
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.覆寫(xiě)onMeasure(…)方法
實(shí)現(xiàn)這個(gè)方法告訴了母容器如何放棄自定義View型宙，可以通過(guò)提供的measureSpecs來(lái)決定你的View的高和寬撬呢，以下是一個(gè)正方形，確認(rèn)它的寬和高是一樣的妆兑。
@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：
這個(gè)方法需要至少保證一個(gè)setMeasuredDimension(..)調(diào)用魂拦，否則會(huì)報(bào)IllegalStateException錯(cuò)誤毛仪。
4.實(shí)現(xiàn)onSizeChanged(…)方法
這個(gè)方法是你獲取View現(xiàn)在的寬和高. 這里我們計(jì)算的是中心和半徑。
@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.實(shí)現(xiàn)onDraw(…)方法
這個(gè)方法提供了如何繪制view芯勘，它提供的Canvas類(lèi)可以進(jìn)行繪制箱靴。
@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
<FrameLayout xmlns:android="http://schemas.android.com/apk/res/android" android:layout_width="match_parent" android:layout_height="match_parent"> <com.example.app.SmileyView android:layout_width="match_parent" android:layout_height="match_parent" /> </FrameLayout>
到此就結(jié)束了，自定義View沒(méi)你想的那么難
