如何使任何视图绘制到画布上? [英] How to make any view to draw to canvas?
问题描述
我有一个简短的问题:
假设我有一个(可变的)位图需要修改(添加图像、文本等...).
Suppose I have a (mutable) bitmap that I need to modify (add images, texts, etc...) .
我没有使用许多特殊的类来绘制画布(油漆、画布、矩阵等),而是在想为什么不使用 Android 的内置类来完成这项任务,而且只有在我需要真正定制的操作时我还能用画布吗?
Instead of messing around with many special classes for drawing to the canvas (paint, canvas, matrices and so on), I was thinking why not use the built in classes of Android for this task and only if i need really customized operations i could still use the canvas ?
因此,例如,为了在位图上显示任何类型的视图(当然没有父视图),我可以调用下一个函数:
So, for example, in order to show any kind of view (that has no parent, of course) on the bitmap, I could call the next function :
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);
}
这种事情可能吗?也许这就是它在幕后工作的方式?
Is such a thing possible? maybe that's even the way that it works behind the scenes?
我应该在绘图和创建画布之间的部分写什么?
what should i write in the part between the drawing and the creation of the canvas?
我试过下一个代码,但没有用:
i've tried the next code , but it didn't work:
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();
}
用法示例:
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);
<小时>
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);
想知道它是否有效.
推荐答案
是的,你可以这样做.请记住,由于您没有将其附加到布局,因此您需要在绘制之前手动对其进行布局:
Yeah, you can do this. Keep in mind, since you're not attaching it to a layout, you'll need to lay it out manually before drawing it:
view.layout(0, 0, viewWidth, viewHeight);
除非您确切地知道这些宽度和高度参数是什么,否则您可能还想先测量它:
And unless you just know exactly what you want for those width and height parameters, you may also want to measure it first:
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());
如果您已经知道所需的宽度和高度:
If you already know the width and height you need:
//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
是的,经过测试.你可以自己试试:
Yes, tested. You can try this yourself:
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);
}
}
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