ScrollView中自定义View不显示

阳光穿透心脏的1/2处 2023-01-17 13:53 147阅读 0赞

public class TextCustomView extends View { 
        public TextCustomView(Context context) { 
            super(context);
            init(context);
        }
    
        public TextCustomView(Context context, @Nullable AttributeSet attrs) { 
            super(context, attrs);
            init(context);
        }
    
        private Paint paint;
    
        private void init(Context context) { 
            paint = new Paint(Paint.ANTI_ALIAS_FLAG);
            paint.setColor(Color.parseColor("#00008a"));
            paint.setTextSize(BaseUtils.dip2px(context, 16));
        }
    
        @Override
        protected void onDraw(Canvas canvas) { 
            super.onDraw(canvas);
            canvas.drawColor(Color.parseColor("#ffebcc"));//来个背景色方便看控件大小
            String txt="换行必须用StaticLayout，drawText只显示一行，不信你看";
            canvas.drawText(txt,10,400,paint);
        }
    }

放在LinearLayout中，显示没问题。

<?xml version="1.0" encoding="utf-8"?>
    <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android" xmlns:app="http://schemas.android.com/apk/res-auto" xmlns:tools="http://schemas.android.com/tools" android:layout_width="match_parent" android:layout_height="match_parent" android:background="@color/white" android:orientation="vertical" tools:context=".InputActivity">
    
        <com.lagou.test.view.input.TextCustomView android:layout_width="match_parent" android:layout_height="wrap_content" />
    
    </LinearLayout>

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2libGFkZQ_size_16_color_FFFFFF_t_70]

然后LinearLayout换成ScrollView之后 不显示了。

重写noMeasure方法：

@Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
            int heightMode = MeasureSpec.getMode(heightMeasureSpec);
            int widthSize = MeasureSpec.getSize(widthMeasureSpec);
            
            if (MeasureSpec.UNSPECIFIED == heightMode) { 
                int heightSize = (int) (widthSize * 1.2f);
                setMeasuredDimension(widthMeasureSpec, heightSize);
            }
        }

这样就可以重新显示了。  
原因是ScrollView的onMeasure并未处理MeasureSpec.UNSPECIFIED。

@Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    
            if (!mFillViewport) { 
                return;
            }
    
            final int heightMode = MeasureSpec.getMode(heightMeasureSpec);
            if (heightMode == MeasureSpec.UNSPECIFIED) { 
                return;
            }
            .......
            .......
          }

父布局遇到MeasureSpec.UNSPECIFIED 直接return，导致子控件默认的测量方式得出的高度就是 初始值 0，所以不显示。此时需要子控件自己处理该case。

上面重写onMeasure可以优化为这样：

@Override
        protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) { 
            super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    
            int heightSize = MeasureSpec.getSize(heightMeasureSpec);
            int reHeight = resolveSize(heightSize, heightMeasureSpec);
            setMeasuredDimension(widthMeasureSpec, reHeight);
        }
    }

resolveSize源码处理了 `case MeasureSpec.UNSPECIFIED:` ，源码如下

public static int resolveSize(int size, int measureSpec) { 
            return resolveSizeAndState(size, measureSpec, 0) & MEASURED_SIZE_MASK;
        }
    
        public static int resolveSizeAndState(int size, int measureSpec, int childMeasuredState) { 
            final int specMode = MeasureSpec.getMode(measureSpec);
            final int specSize = MeasureSpec.getSize(measureSpec);
            final int result;
            switch (specMode) { 
                case MeasureSpec.AT_MOST:
                    if (specSize < size) { 
                        result = specSize | MEASURED_STATE_TOO_SMALL;
                    } else { 
                        result = size;
                    }
                    break;
                case MeasureSpec.EXACTLY:
                    result = specSize;
                    break;
                case MeasureSpec.UNSPECIFIED:
                default:
                    result = size;
            }
            return result | (childMeasuredState & MEASURED_STATE_MASK);
        }

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2libGFkZQ_size_16_color_FFFFFF_t_70]: /images/20221021/7904881e6c0d4fddb6e6475d53eb607a.png