绘制/布局期间的对象分配

Question

我在绘制/布局期间获得3个对象分配警告

super.onDraw(canvas);
canvas.drawColor(Color.WHITE);
Paint textPaint = new Paint();
textPaint.setARGB(50,100,100,250);
textPaint.setTextAlign(Align.CENTER);
textPaint.setTextSize(50);
textPaint.setTypeface(font);
canvas.drawText("Logan is awesom",canvas.getWidth()/2,200,textPaint);
canvas.drawBitmap(pBall, (canvas.getWidth()/2), changingY, null);
if (changingY <canvas.getHeight()){
changingY += 10;
}else{
changingY=0;
}
Rect middleRect = new Rect();
middleRect.set(0, 400, canvas.getWidth(), 550);
Paint ourBlue = new Paint();
ourBlue.setColor(Color.BLUE);
canvas.drawRect(middleRect, ourBlue);

我得到一个错误的新Rect();和new Paint();

确切的错误是在绘制/布局操作期间避免对象分配(而不是预先定位和重用)

Answer 1

好吧，你的"错误"指出了确切的问题。onDraw()方法被操作系统多次调用，因此在这个函数中分配一些东西是非常糟糕的主意。您需要事先分配您的Rect和Paint，并且只在onDraw内使用它们

class YourClass extends View
{
    Rect middleRect;
    Paint ourBlue;
    Paint textPaint;
    public YourClass()
    {
         //constructor
         init();
    }
    private void init()
    {
        middleRect = new Rect();
        ourBlue; = new Paint();
        textPaint = new Paint();
        ourBlue.setColor(Color.BLUE);
        textPaint.setARGB(50,100,100,250);
        textPaint.setTextAlign(Align.CENTER);
        textPaint.setTextSize(50);
        textPaint.setTypeface(font);
    }
    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        canvas.drawColor(Color.WHITE);
        canvas.drawText("Logan is awesom",canvas.getWidth()/2,200,textPaint);
        canvas.drawBitmap(pBall, (canvas.getWidth()/2), changingY, null);
        if (changingY <canvas.getHeight()){
            changingY += 10;
        }else{
            changingY=0;
        }
        //if canvas size doesn't change - this can be moved to init() as well
        middleRect.set(0, 400, canvas.getWidth(), 550);
        canvas.drawRect(middleRect, ourBlue);
    }
}

Answer 2

对于我来说，我在布局中遇到了这个错误，特别是在使用显示度量时。

我已经使用了这个imageview:

   <com.steve.thirdparty.ScalableImageView
        android:id="@+id/iv_posted_img_home"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:scaleType="fitXY"
        android:background="@drawable/golive_load_image"
        android:layout_below="@+id/tv_user_posted_msg_post_items_home"
        android:contentDescription="@string/cont_desc"/>

ScalableImageView.java:

导入静态com.steve.TabHomeActivity.displaymetrics;

public class ScalableImageView extends ImageView {

        ((Activity) getContext()).getWindowManager().getDefaultDisplay().getMetrics(displaymetrics);
}

我通过在Activity的onCreate()方法中添加静态DisplayMetrices解决了这个问题。

TabHomeActivity.java:

public static DisplayMetrics displaymetrics;
*inside onCreate()*
 displaymetrics = new DisplayMetrics();

Answer 3

在绘制/布局操作中避免对象分配(预先定位和重用)

留言给你一个解决方案，所以我不明白你的问题是什么

你必须将新对象的创建移动到onCreate方法，所以它们只创建一次，然后在onDraw方法中使用它们。