自定义view单位的转化、状态保存等

自定义view单位的转化

//dp转px
int minWidth = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, 120, 
getContext().getResources().getDisplayMetrics());

//sp转px
int minHeight = (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP, 80, 
getContext().getResources().getDisplayMetrics());


 /**
     * 根据手机的分辨率从 dp 的单位 转成为 px(像素)
     */
    public static int dip2px(Context context, float dpValue) {
        final float scale = context.getResources().getDisplayMetrics().density;
        return (int) (dpValue * scale + 0.5f);
    }

工具类：

public class DensityUtils {  
    private DensityUtils() {  
        /* cannot be instantiated */  
        throw new UnsupportedOperationException("cannot be instantiated");  
    }  

    public static int dp2px(Context context, float dpVal) {
        return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP,  
                dpVal, context.getResources().getDisplayMetrics());  
    }  

    public static int sp2px(Context context, float spVal) {
        return (int) TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_SP,  
                spVal, context.getResources().getDisplayMetrics());  
    }  

    public static float px2dp(Context context, float pxVal) {
        final float scale = context.getResources().getDisplayMetrics().density;  
        return (pxVal / scale);  
    }  

    public static float px2sp(Context context, float pxVal) {
        return (pxVal / context.getResources().getDisplayMetrics().scaledDensity);  
    }  
}  

自定义view状态的保存

  private static final String STATE_INSTANCE = "state_instance";
    private static final String STATE_TYPE = "state_type";
    private static final String STATE_BORDER_RADIUS = "state_border_radius";

    private int type;
    private int mBorderRadius;

    @Override
    protected Parcelable onSaveInstanceState() {
        Bundle bundle = new Bundle();
        bundle.putParcelable(STATE_INSTANCE, super.onSaveInstanceState());
        bundle.putInt(STATE_TYPE, type);
        bundle.putInt(STATE_BORDER_RADIUS, mBorderRadius);
        return bundle;
    }

    @Override
    protected void onRestoreInstanceState(Parcelable state) {
        if (state instanceof Bundle) {
            Bundle bundle = (Bundle) state;
            super.onRestoreInstanceState(((Bundle) state).getParcelable(STATE_INSTANCE));
            this.type = bundle.getInt(STATE_TYPE);
            this.mBorderRadius = bundle.getInt(STATE_BORDER_RADIUS);
        } else {
            super.onRestoreInstanceState(state);
        }
    }

自定义view的常用的onmeasure方法

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

    setMeasuredDimension(getMeasuredWidth(), getMeasuredHeight()/2);
}

系统默认：

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
  setMeasuredDimension(getDefaultSize(getSuggestedMinimumWidth(), widthMeasureSpec),
          getDefaultSize(getSuggestedMinimumHeight(), heightMeasureSpec));
}
public static int getDefaultSize(int size, int measureSpec) {
  int result = size;
  int specMode = MeasureSpec.getMode(measureSpec);
  int specSize = MeasureSpec.getSize(measureSpec);

  switch (specMode) {
  case MeasureSpec.UNSPECIFIED:
      result = size;
      break;
  case MeasureSpec.AT_MOST:
  case MeasureSpec.EXACTLY:
      result = specSize;
      break;
  }
  return result;
}

系统默认wrap_content和match_parent效果一样，测量宽高都是specSize，而这个specSize正是父控件剩余的宽高，所以默认onMeasure方法中wrap_content 和match_parent 的效果是一样的，都是填充剩余的空间。

参考：Android自定义View（一、初体验自定义TextView）

考虑wrap_content：

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    super.onMeasure(widthMeasureSpec, heightMeasureSpec);
    int widthMode = MeasureSpec.getMode(widthMeasureSpec);   //获取宽的模式
    int heightMode = MeasureSpec.getMode(heightMeasureSpec); //获取高的模式
    int widthSize = MeasureSpec.getSize(widthMeasureSpec);   //获取宽的尺寸
    int heightSize = MeasureSpec.getSize(heightMeasureSpec); //获取高的尺寸

    int width;
    int height ;
    if (widthMode == MeasureSpec.EXACTLY) {
        //如果match_parent或者具体的值，直接赋值
        width = widthSize;
    } else {
        //如果是wrap_content，我们要得到控件需要多大的尺寸
        float textWidth = mBound.width();   //文本的宽度
        //控件的宽度就是文本的宽度加上两边的内边距。内边距就是padding值，在构造方法执行完就被赋值
        width = (int) (getPaddingLeft() + textWidth + getPaddingRight());
    }
    //高度跟宽度处理方式一样
    if (heightMode == MeasureSpec.EXACTLY) {
        height = heightSize;
    } else {
        float textHeight = mBound.height();
        height = (int) (getPaddingTop() + textHeight + getPaddingBottom());
    }

    //保存测量宽度和测量高度
    setMeasuredDimension(width, height);
}

接口的定义示例：

    private OnLoadingCompleteListenter onLoadingCompleteListenter;

   interface OnLoadingCompleteListenter {
        void onComplete();
    }

    public OnLoadingCompleteListenter getOnLoadingCompleteListenter() {
        return onLoadingCompleteListenter;
    }

    public void setOnLoadingCompleteListenter(OnLoadingCompleteListenter onLoadingCompleteListenter) {
        this.onLoadingCompleteListenter = onLoadingCompleteListenter;
    }