java - 错误: The specified child already has a parent

Question

在我的程序中，我的模拟器上出现此错误。 如果我在 Razr MAXX 上运行它，它可以工作吗？它说

10-28 19:38:27.935: E/AndroidRuntime(2268): java.lang.IllegalStateException: The specified child already has a parent. You must call removeView() on the child's parent first.

错误发生在这一行:layout.addView(mid)

我相信它说 mid 已经有一个父级，所以我用 ViewGroupparent = (ViewGroup) mid.getParent(); 进行调试，它返回 null...

有人可以引导我走向正确的方向吗？

下面是我的类(class):

package com.example.draganddroptest;

import android.content.Context;
import android.content.res.TypedArray;
import android.graphics.Canvas;
import android.graphics.Paint;
import android.graphics.PointF;
import android.util.AttributeSet;
import android.view.View;
import android.view.ViewGroup;

/**
 * @author Brandon Ling
 * 
 */
public class HoneycombView extends View {
    private Context context;
    private ViewGroup layout;
    private HexagonView top;
    private HexagonView topRight;
    private HexagonView topLeft;
    private HexagonView bot;
    private HexagonView botLeft;
    private HexagonView botRight;
    private HexagonView mid;
    private int radius;
    private PointF shift;
    private String color;
    private String[] colors;
    private int strokeWidth;

    Paint paint = new Paint();

    /**
     * @param context
     * @param layout
     */
    public HoneycombView(Context context, AttributeSet attrs) {
        this(context, null, 0, null, null, attrs, 0);
    }

    public HoneycombView(Context context, ViewGroup layout, int radius, PointF shift, String color, AttributeSet attrs, int strokeWidth) {
        super(context);
        this.context = context;

        if (attrs != null) { // probably sent via xml
            TypedArray a = context.obtainStyledAttributes(attrs, R.styleable.HoneycombView);
            this.radius = a.getInt(R.styleable.HoneycombView_radius, this.strokeWidth);
            this.shift = new PointF(a.getInt(R.styleable.HoneycombView_shiftX, 0), a.getInt(
                    R.styleable.HoneycombView_shiftY, 0));
            this.colors = a.getString(R.styleable.HoneycombView_hexColors).split("\\|");
            a.recycle();
        } else {
            this.layout = layout;
            this.radius = radius;
            this.shift = shift;
            this.color = color;
        }
        this.mid = new HexagonView(this.context, null, this.radius, this.shift, this.colors[0], 10);
        this.top = mid.addHexTop(colors[1]);
        this.topRight = mid.addHexTopRight(colors[2]);
        this.topLeft = mid.addHexTopLeft(colors[3]);
        this.bot = mid.addHexBot(colors[4]);
        this.botRight = mid.addHexBotRight(colors[5]);
        this.botLeft = mid.addHexBotLeft(colors[6]);
    }

    @Override
    protected void onDraw(Canvas canvas) {
        super.onDraw(canvas);
        this.layout = (ViewGroup) this.getParent();
        ViewGroup parent = (ViewGroup) mid.getParent();
        //parent.removeAllViews();
        layout.addView(mid);
        layout.addView(top);
        layout.addView(topRight);
        layout.addView(topLeft);
        layout.addView(bot);
        layout.addView(botRight);
        layout.addView(botLeft);


    }

    @Override
    protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
        int height = (int) Math.ceil(this.bot.getMaxY()) + this.strokeWidth;
        int width = (int) Math.ceil(this.botRight.getMaxX()) + this.strokeWidth;
        setMeasuredDimension(width, height);
    }
}

Answer 1

1. onDraw() 由 Android 重复调用。第二次调用 onDraw() 将引发此异常，因为每个 View 已添加到父级。

2. 也就是说，通常来说，您永远不会更改 onDraw() 内的布局。此方法仅用于在 Canvas 上绘画。即使您设法通过调用 removeAllViews() 来修复此异常(看起来您可能已经尝试过)，您也将迫使 Android 在 View 被删除和删除时不断地一次又一次地测量和绘制布局。重新添加。

3. 您可能实际上并不希望将 subview 添加到父 View 中。如果要添加 subview ，则应将它们添加为 HoneyCombView 的 subview 。为此，您需要扩展 ViewGroup 而不是 View。再次，将 subview 添加到其他位置，而不是在 onDraw() 中。

4. 虽然将 subview 添加到 ViewGroup 可以，但它对性能不太好。添加到布局中的每个 subview 都会减慢应用程序的速度。 (参见 Use Fewer Views 。)更好的替代方法是使用(例如)canvas.drawPath() 将形状直接绘制到 Canvas 上。

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