创建多层绘图时，会出现避免对象分配警告

Question

使用Java创建digram后，3个区域会突出显示并因某些原因返回警告。我不确定为什么会这样。如何摆脱这种警告呢？

  

在绘制/布局操作期间避免对象分配（预分配和重用）

public class Diagram extends View {
    private int measuredWidth, measuredHeight;
    private Paint mBackgroundPaint, mYellowLinePaint, mWhiteLinePaint;
    private RectF mBackgroundRect, mYellowLineRectF, mWhiteLineRectF;


    public Diagram(Context context) {
        super(context);
        init(context, null, 0);
    }

    public Diagram(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs, 0);
    }

    public Diagram(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs, defStyleAttr);
    }

    private void init(Context context, AttributeSet attributeSet, int defStyle) {

        mBackgroundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mBackgroundPaint.setColor(0xFF3C3C3C);
        mBackgroundPaint.setStyle(Paint.Style.FILL);

        mYellowLinePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mYellowLinePaint.setColor(0xFFFFFF00);
        mYellowLinePaint.setStyle(Paint.Style.FILL);

        mWhiteLinePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mWhiteLinePaint.setColor(0xFFFFFFFF);
        mWhiteLinePaint.setStyle(Paint.Style.FILL);
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        measuredHeight = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        measuredWidth = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

        mBackgroundRect = new RectF(0, 0, measuredWidth, measuredHeight);
        mYellowLineRectF = new RectF(0, 0.2f * measuredHeight, measuredWidth, 0.3f * measuredHeight);
        mWhiteLineRectF = new RectF(0, 0.0f * measuredHeight, measuredWidth, 0.1f * measuredHeight);

        setMeasuredDimension(measuredWidth, measuredHeight);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        if (measuredHeight == 0 || measuredWidth == 0)
            return;

        canvas.drawRect(mBackgroundRect, mBackgroundPaint);
        canvas.drawRect(mYellowLineRectF, mYellowLinePaint);
        canvas.drawRect(mWhiteLineRectF, mWhiteLinePaint);
    }
}

更新了代码

public class Diagram extends View {
    private int measuredWidth, measuredHeight;
    private Paint mBackgroundPaint, mYellowLinePaint, mWhiteLinePaint;

    private final RectF mBackgroundRect = new RectF();
    private final RectF mYellowLineRectF = new RectF();
    private final RectF mWhiteLineRectF = new RectF();

    public Diagram(Context context) {
        super(context);
        init(context, null, 0);
    }

    public Diagram(Context context, AttributeSet attrs) {
        super(context, attrs);
        init(context, attrs, 0);
    }

    public Diagram(Context context, AttributeSet attrs, int defStyleAttr) {
        super(context, attrs, defStyleAttr);
        init(context, attrs, defStyleAttr);
    }

    private void init(Context context, AttributeSet attributeSet, int defStyle) {

        mBackgroundPaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mBackgroundPaint.setColor(0xFF3C3C3C);
        mBackgroundPaint.setStyle(Paint.Style.FILL);

        mYellowLinePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mYellowLinePaint.setColor(0xFFFFFF00);
        mYellowLinePaint.setStyle(Paint.Style.FILL);

        mWhiteLinePaint = new Paint(Paint.ANTI_ALIAS_FLAG);
        mWhiteLinePaint.setColor(0xFFFFFFFF);
        mWhiteLinePaint.setStyle(Paint.Style.FILL);
    }


    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        measuredHeight = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        measuredWidth = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

        mBackgroundRect.set(0, 0, measuredWidth, measuredHeight);
        mYellowLineRectF.set(0, 0.2f * measuredHeight, measuredWidth, 0.3f * measuredHeight);
        mWhiteLineRectF.set(0, 0.0f * measuredHeight, measuredWidth, 0.1f * measuredHeight);

        setMeasuredDimension(measuredWidth, measuredHeight);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);

        if (measuredHeight == 0 || measuredWidth == 0)
            return;

        canvas.drawRect(mBackgroundRect, mBackgroundPaint);
        canvas.drawRect(mYellowLineRectF, mYellowLinePaint);
        canvas.drawRect(mWhiteLineRectF, mWhiteLinePaint);
    }
}

Answer 1

在类构造函数或字段初始值设定项中创建一次3 RectF个实例，然后在RectF.set()中使用onMeasure()。

public class Diagram extends View {
    private final RectF mBackgroundRect = new RectF();
    private final RectF mYellowLineRectF = new RectF();
    private final RectF mWhiteLineRectF = new RectF();

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);
        measuredHeight = getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec);
        measuredWidth = getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec);

        mBackgroundRect.set(0, 0, measuredWidth, measuredHeight);
        mYellowLineRectF.set(0, 0.2f * measuredHeight, measuredWidth, 0.3f * measuredHeight);
        mWhiteLineRectF.set(0, 0.0f * measuredHeight, measuredWidth, 0.1f * measuredHeight);

        setMeasuredDimension(measuredWidth, measuredHeight);
    }
}