内存优化（一）：内存抖动和内存泄漏

LMK；内存抖动、内存泄漏与内存溢出
优化的结果：使得app流畅不卡

内存抖动

短时间内有大量对象创建与销毁，它伴随着频繁的GC。

比较典型的就是字符串的拼接造成内存抖动。

比如:

String str = "";
for(int i=0; i< 10; i++) {
    str += i;
}

+=操作会编译成StringBuilder对象，然后调用StringBuilder的append方法进行拼接。
所以上述代码会创建10个StringBuilder对象，每执行一次+操作都会新创建一个StringBuilder对象。

优化方法：避免使用+或者+=操作，使用StringBuilder来实现字符串的拼接

StringBuilder str = new StringBuilder();
for (int i = 0; i < 10; i++) {
   
    str.append(i);
}

内存抖动实战

一个不断旋转的试图，优化前的代码：

public class IOSStyleLoadingView1 extends View {
   

    private final Context context;
    private double radius;
    private double insideRadius;
    private float northwestXStart;
    private float northwestYStart;
    private float northXStart;
    private float northYStart;
    private float notheastXStart;
    private float notheastYStart;
    private float eastXStart;
    private float eastYStart;
    private float southeastXStart;
    private float southeastYStart;
    private float southXStart;
    private float southYStart;
    private float southwestXStart;
    private float southwestYStart;
    private float westXStart;
    private float westYStart;

    private float northwestXEnd;
    private float northwestYEnd;
    private float northXEnd;
    private float northYEnd;
    private float notheastXEnd;
    private float notheastYEnd;
    private float eastXEnd;
    private float eastYEnd;
    private float southeastXEnd;
    private float southeastYEnd;
    private float southXEnd;
    private float southYEnd;
    private float southwestXEnd;
    private float southwestYEnd;
    private float westXEnd;
    private float westYEnd;

    private int currentColor = 7;

    String color[] = new String[]{
   
            "#a5a5a5",
            "#b7b7b7",
            "#c0c0c0",
            "#c9c9c9",
            "#d2d2d2",
            "#dbdbdb",
            "#e4e4e4",
            "#e4e4e4"
    };

    public IOSStyleLoadingView1(Context context) {
   
        this(context,null,0);
    }

    public IOSStyleLoadingView1(Context context, AttributeSet attrs) {
   
        this(context,null,0);
    }

    public IOSStyleLoadingView1(Context context, AttributeSet attrs, int defStyleAttr) {
   
        super(context, attrs, defStyleAttr);
        this.context = context;
        radius = UIKits.dip2Px(context, 9);
        insideRadius = UIKits.dip2Px(context, 5);
    }

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

        Paint paint = new Paint();
        paint.setAntiAlias(true);
        paint.setStrokeWidth(UIKits.dip2Px(context, 2));
        paint.setStyle(Paint.Style.STROKE);
        paint.setStrokeCap(Paint.Cap.ROUND);

        Path p0 = new Path();
        paint.setColor(Color.parseColor(color[0]));//Color.parseColor方法会调用String的substring()方法，substring()方法会产生新的String对象
        p0.moveTo(northwestXStart, northwestYStart);
        p0.lineTo(northwestXEnd, northwestYEnd);
        canvas.drawPath(p0, paint);

        Path p1 = new Path();
        paint.setColor(Color.parseColor(color[1]));
        p1.moveTo(northXStart, northYStart);
        p1.lineTo(northXEnd, northYEnd);
        canvas.drawPath(p1, paint);

        Path p2 = new Path();
        paint.setColor(Color.parseColor(color[2]));
        p2.moveTo(notheastXStart, notheastYStart);
        p2.lineTo(notheastXEnd, notheastYEnd);
        canvas.drawPath(p2, paint);

        Path p3 = new Path();
        paint.setColor(Color.parseColor(color[3]));
        p3.moveTo(eastXStart, eastYStart);
        p3.lineTo(eastXEnd, eastYEnd);
        canvas.drawPath(p3, paint);

        Path p4 = new Path();
        paint.setColor(Color.parseColor(color[4]));
        p4.moveTo(southeastXStart, southeastYStart);
        p4.lineTo(southeastXEnd, southeastYEnd);
        canvas.drawPath(p4, paint);

        Path p5 = new Path();
        paint.setColor(Color.parseColor(color[5]));
        p5.moveTo(southXStart, southYStart);
        p5.lineTo(southXEnd, southYEnd);
        canvas.drawPath(p5, paint);

        Path p6 = new Path();
        paint.setColor(Color.parseColor(color[6]));
        p6.moveTo(southwestXStart, southwestYStart);
        p6.lineTo(southwestXEnd, southwestYEnd);
        canvas.drawPath(p6, paint);

        Path p7 = new Path();
        paint.setColor(Color.parseColor(color[7]));
        p7.moveTo(westXStart, westYStart);
        p7.lineTo(westXEnd, westYEnd);
        canvas.drawPath(p7, paint);

    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
   
        super.onMeasure(widthMeasureSpec, heightMeasureSpec);