如何使任何视图绘制到画布？

Question

我有一个简短的问题：

假设我有一个（可变的）位图，我需要修改（添加图像，文本等...）。

我想，为什么不使用Android的内置类来完成这个任务，而且只有当我需要真正定制时才会使用很多特殊的类来绘制画布（油漆，画布，矩阵等等）我仍然可以使用画布的操作？

因此，举例来说，为了表现出任何一种观点（即没有父，当然）的位图，我可以打电话给下一个功能：

public void drawViewToBitmap(Bitmap b, View v, Rect rect) { 
    Canvas c = new Canvas(b); 
    // <= use rect to let the view to draw only into this boundary inside the bitmap 
    view.draw(c); 
} 

这种事可能吗？也许这就是它在幕后工作的方式？

我应该在绘图和创建画布之间的部分写什么？

---

编辑：我试了下代码，但没有奏效：

final int imageSize = 50; 
rect = new Rect(35, 344 , 35 + imageSize, 344 + imageSize); 
final ImageView imageView = new ImageView(mContext); 
imageView.setImageBitmap(bitmap); 
imageView.setScaleType(ScaleType.CENTER_CROP); 
drawFromViewToCanvas(imageView, getRect(), canvas); 

---

编辑：使用的

public void drawFromViewToCanvas(final View view, final Rect rect, final Canvas canvas) { 
    final int widthSpec = View.MeasureSpec.makeMeasureSpec(rect.width(), View.MeasureSpec.EXACTLY); 
    final int heightSpec = View.MeasureSpec.makeMeasureSpec(rect.height(), View.MeasureSpec.EXACTLY); 
    view.measure(widthSpec, heightSpec); 
    // Lay the view out with the known dimensions 
    view.layout(0, 0, rect.width(), rect.height()); 
    // Translate the canvas so the view is drawn at the proper coordinates 
    canvas.save(); 
    canvas.translate(rect.left, rect.top); 
    // Draw the View and clear the translation 
    view.draw(canvas); 
    canvas.restore(); 
} 

比如有一个样品上sony's website：

int measureWidth = View.MeasureSpec.makeMeasureSpec(bitmapWidth, View.MeasureSpec.EXACTLY); 
int measuredHeight = View.MeasureSpec.makeMeasureSpec(bitmapHeight, View.MeasureSpec.EXACTLY); 
view.measure(measureWidth, measuredHeight); 
view.layout(0, 0, bitmapWidth, bitmapHeight); 
view.draw(canvas); 

不知道它是否有效。

Answer 1

是的，你可以做到这一点。请记住，因为你不将其连接到布局，你需要绘制它之前手动摊开来：

view.layout(0, 0, viewWidth, viewHeight); 

，除非你只知道你想要什么对于那些宽度和高度参数，你可能还需要先衡量它：

int widthSpec = MeasureSpec.makeMeasureSpec (ViewGroup.LayoutParams.WRAP_CONTENT, MeasureSpec.UNSPECIFIED; 
int heightSpec = MeasureSpec.makeMeasureSpec (400, MeasureSpec.UNSPECIFIED; 
view.measure(widthSpec, heightSpec); 
view.layout(0, 0, view.getMeasuredWidth(), view.getMeasuredHeight()); 

编辑：

如果你已经知道的宽度和高度，你需要：

//Lay the view out with the known dimensions 
view.layout (0, 0, rect.width(), rect.height()); 

//Translate the canvas so the view is drawn at the proper coordinates 
canvas.save(); 
canvas.translate(rect.left, rect.top); 

//Draw the View and clear the translation 
view.draw(canvas); 
canvas.restore(); 

再次编辑：

是的，经过测试。你可以自己试试这个：

public class DrawingActivity extends Activity { 
    public void onCreate (Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 

     //Set a Rect for the 200 x 200 px center of a 400 x 400 px area 
     Rect rect = new Rect(); 
     rect.set(100, 100, 300, 300); 

     //Allocate a new Bitmap at 400 x 400 px 
     Bitmap bitmap = Bitmap.createBitmap(400, 400, Bitmap.Config.ARGB_8888); 
     Canvas canvas = new Canvas(bitmap); 

     //Make a new view and lay it out at the desired Rect dimensions 
     TextView view = new TextView(this); 
     view.setText("This is a custom drawn textview"); 
     view.setBackgroundColor(Color.RED); 
     view.setGravity(Gravity.CENTER); 

     //Measure the view at the exact dimensions (otherwise the text won't center correctly) 
     int widthSpec = View.MeasureSpec.makeMeasureSpec(rect.width(), View.MeasureSpec.EXACTLY); 
     int heightSpec = View.MeasureSpec.makeMeasureSpec(rect.height(), View.MeasureSpec.EXACTLY); 
     view.measure(widthSpec, heightSpec); 

     //Lay the view out at the rect width and height 
     view.layout(0, 0, rect.width(), rect.height()); 

     //Translate the Canvas into position and draw it 
     canvas.save(); 
     canvas.translate(rect.left, rect.top); 
     view.draw(canvas); 
     canvas.restore(); 

     //To make sure it works, set the bitmap to an ImageView 
     ImageView imageView = new ImageView(this); 
     imageView.setLayoutParams(new ViewGroup.LayoutParams(ViewGroup.LayoutParams.MATCH_PARENT, ViewGroup.LayoutParams.MATCH_PARENT)); 
     setContentView(imageView); 
     imageView.setScaleType(ImageView.ScaleType.CENTER); 
     imageView.setImageBitmap(bitmap); 
    } 
}