在android上为自定义动态视图实现放大镜/放大镜

Question

我正在寻找一种方法来实现放大镜/放大镜，以便在动态重建的 android 上实现自定义视图。

Answer 1

我开这门课只是为了回答你的问题。这是放大镜的最基本实现，希望对您有所帮助。祝你好运：

public class ExampleMagnifierView extends View {

Matrix matrix = new Matrix();
Paint shaderPaint = new Paint();
BitmapShader shader = null;
//start the magnifier
boolean zooming;
//capture a new bitmap form a view
boolean isFirstTouch = true;
//magnifier position
static final PointF zoomPos = new PointF(0, 0);

private float magnifierSize = 75;
private Context context = null;
private Bitmap someBitmap = null;

ArrayList<Element> elements = new ArrayList<Element>();

public ExampleMagnifierView(Context context, AttributeSet attrs) {
    super(context, attrs);

    this.context = context;

    //Just for the example
    someBitmap = BitmapFactory.decodeResource(getResources(), android.R.drawable.ic_delete);

    //Just for the example
    elements = prepareElementsMatrix(5, 6);
}

@Override
protected void onDraw(Canvas canvas) {

    drawSomethingToBeMagnifiedNoMatterWhat(canvas);

    if (zooming) {
        matrix.reset();
        matrix.postScale(2f, 2f, zoomPos.x, zoomPos.y);
        shaderPaint.getShader().setLocalMatrix(matrix);
        canvas.drawCircle(zoomPos.x, zoomPos.y, convertDpToPixel(magnifierSize, this.getContext()), shaderPaint);
    }

}

private void drawSomethingToBeMagnifiedNoMatterWhat(Canvas canvas){

    for (Element el : elements){
        canvas.drawBitmap(someBitmap, el.x , el.y , null);
    }

}

@Override
public boolean onTouchEvent(MotionEvent event) {

    if (isFirstTouch) {
        //we set the zooming to false because we want a image of the view without magnifier
        zooming = false;

        shader = null;
        shaderPaint = null;
        shaderPaint = new Paint();

        //get a fresh bitmap from the view
        shader = new BitmapShader(getBitmapFromView(this), Shader.TileMode.CLAMP, Shader.TileMode.CLAMP);
        isFirstTouch = false;
    }

    shaderPaint.setShader(shader);
    matrix.reset();
    matrix.postTranslate(-zoomPos.x, -zoomPos.y - convertDpToPixel(magnifierSize, context));
    shader.setLocalMatrix(matrix);

    switch (event.getAction()) {
        case MotionEvent.ACTION_DOWN:

            zoomPos.x = event.getX();
            zoomPos.y = event.getY() - convertDpToPixel(magnifierSize, context);

            //this flag starts drawing the magnifier
            zooming = true;
            invalidate();

            isFirstTouch = true;


            break;
        case MotionEvent.ACTION_MOVE:

            zoomPos.x = event.getX();
            zoomPos.y = event.getY() - convertDpToPixel(magnifierSize, context);

            //this flag starts drawing the magnifier
            zooming = true;
            invalidate();

            break;

        case MotionEvent.ACTION_UP:
        case MotionEvent.ACTION_CANCEL:

            isFirstTouch = true;
            zooming = false;
            invalidate();

            break;
    }

    return true;

}

/**
 * This method get the bitmap form a view.
 *
 * @param view The view who we want as a bitmap
 * @return The view's bitmap
 */
public static Bitmap getBitmapFromView(View view) {
    //Define a bitmap with the same size as the view ( Use RGB_565 for better performance )
    Bitmap returnedBitmap = Bitmap.createBitmap(view.getWidth(), view.getHeight(), Bitmap.Config.RGB_565);
    //Bind a canvas to it
    Canvas canvas = new Canvas(returnedBitmap);
    //Get the view's background
    Drawable bgDrawable = view.getBackground();
    if (bgDrawable != null) {
        //has background drawable, then draw it on the canvas
        bgDrawable.draw(canvas);
    } else {
        //does not have background drawable, then draw white background on the canvas
        canvas.drawColor(Color.WHITE);
    }
    // draw the view on the canvas
    view.draw(canvas);

    //erase the drawable
    bgDrawable = null;

    //return the bitmap
    return returnedBitmap;
}

/**
 * This method converts dp unit to equivalent pixels, depending on device density.
 *
 * @param dp      A value in dp (density independent pixels) unit. Which we need to convert into pixels
 * @param context Context to get resources and device specific display metrics
 * @return A float value to represent px equivalent to dp depending on device density
 */
public static float convertDpToPixel(float dp, Context context) {
    Resources resources = context.getResources();
    DisplayMetrics metrics = resources.getDisplayMetrics();
    float px = dp * (metrics.densityDpi / 160f);
    return px;
}

private ArrayList<Element> prepareElementsMatrix(int rows, int columns){
    ArrayList<Element> elementsMatrix = new ArrayList<Element>();
    int offsetX = 0;
    int offsetY = 0;

    for (int i = 0; i<=columns; i++){

        offsetX += someBitmap.getWidth() + 5;
        elementsMatrix.add(new Element(offsetX, offsetY));
        for (int j = 0; j<=rows; j++){
            elementsMatrix.add(new Element(offsetX, offsetY));
            offsetY += someBitmap.getHeight() + 5;
        }

        offsetY = 0;
    }

    return elementsMatrix;
}

private class Element{
    int x;
    int y;

    public Element(int x, int y){
        this.x = x;
        this.y = y;
    }

}

Answer 2

我自己弄明白了。 所以这里是动态变化视图的变体。

1) 首先，我们在 Overriden on Draw 方法中创建具有相同高度和宽度的新位图（整体）；

2) 从我们的位图（整体）创建 Canvas(temporalCanvas)

3) 在 canvas(temporalCanvas) 上绘制我们需要的一切

4) 将位图绘制到onDraw收益中给出的原始画布(canvas)

5) 从 MotionEvent 获取坐标（它应该在 ACTION_DOWN 上设为全局静态），因此这将是无效和绘制视图后的 SAME MotionEvent

6) 围绕选定(MotionEvent.GetX/Y) 位置剪切位图

7) 在原始（画布）画布上绘制修剪过的位图

可能的困难： -Motion 事件在从覆盖的 onTouchEvent 或从 ACTION_DOWN 上进行的静态事件调用时返回不同的坐标 X、Y； （只需将 x,y 坐标设为静态）并且不要忘记删除静态触摸事件，以及动作 UP 上的 x,y 坐标

应该使用-2画布或者你可以放大镜放大镜）