安卓在API级别28中找不到画布变量

Question

在Android 28中找不到以下Canvas变量

canvas.saveLayer(0, 0, getWidth(), getHeight(), null,
                Canvas.MATRIX_SAVE_FLAG |
                        Canvas.CLIP_SAVE_FLAG |
                        Canvas.HAS_ALPHA_LAYER_SAVE_FLAG |
                        Canvas.FULL_COLOR_LAYER_SAVE_FLAG |
                        Canvas.CLIP_TO_LAYER_SAVE_FLAG);

Answer 1

你可以用canvas.save();代替canvas.save(Canvas.MATRIX_SAVE_FLAG|CLIP_SAVE_FLAG) 参考文献

Answer 2

这些标志已在API 28中删除。见here：

Class android.graphics.Canvas

Removed Methods int save(int)

Removed Fields int CLIP_SAVE_FLAG
int CLIP_TO_LAYER_SAVE_FLAG
int FULL_COLOR_LAYER_SAVE_FLAG
int HAS_ALPHA_LAYER_SAVE_FLAG
int MATRIX_SAVE_FLAG

该方法在API 26中被弃用。见here：

This method was deprecated in API level 26. Use saveLayer(float, float, float, float, Paint) instead.

改用什么

根据API 28的Canvas源代码，您使用的所有标志组合起来等于ALL_SAVE_FLAG的值：

public  static  final  int ALL_SAVE_FLAG =  0x1F;
public  static  final  int MATRIX_SAVE_FLAG =  0x01;
public  static  final  int CLIP_SAVE_FLAG =  0x02;
public  static  final  int HAS_ALPHA_LAYER_SAVE_FLAG =  0x04;
public  static  final  int FULL_COLOR_LAYER_SAVE_FLAG =  0x08;
public  static  final  int CLIP_TO_LAYER_SAVE_FLAG =  0x10;

从同一个source code调用Canvas#saveLayer(left, top, right, bottom, paint)默认使用ALL_SAVE_FLAG：

/**  
 * Convenience for {@link #saveLayer(RectF, Paint)} that takes the four float coordinates of the  
 * bounds rectangle. */
public int saveLayer(float left, float top, float right, float bottom, @Nullable Paint paint) {  
    return saveLayer(left, top, right, bottom, paint, ALL_SAVE_FLAG);  
}

因此，看起来您的代码相当于以下代码，您可以将其用作替换：

canvas.saveLayer(0, 0, getWidth(), getHeight(), null);

此版本的saveLayer（）仅在API 21+上可用。要支持较低的API级别，请使用

canvas.saveLayer(0, 0, getWidth(), getHeight(), null, Canvas.ALL_SAVE_FLAG);

其中Canvas.ALL_SAVE_FLAG与上面的或'ed值相同