Android自定义View之Layout的放缩（2）

只有一个子节点时可放缩的Framelayout,详细代码如下：

import android.content.Context;import android.util.AttributeSet;import android.util.Log;import android.view.MotionEvent;import android.view.ScaleGestureDetector;import android.view.View;import android.widget.FrameLayout; /** * Layout that provides pinch-zooming of content. This view should have exactly one child * view containing the content. */public class ZoomLayout extends FrameLayout implements ScaleGestureDetector.OnScaleGestureListener {  private enum Mode {    NONE,    DRAG,    ZOOM  }  private static final String TAG = "ZoomLayout";  private static final float MIN_ZOOM = 1.0f;  private static final float MAX_ZOOM = 4.0f;  private Mode mode = Mode.NONE;  private float scale = 1.0f;  private float lastScaleFactor = 0f;  // Where the finger first  touches the screen  private float startX = 0f;  private float startY = 0f;  // How much to translate the canvas  private float dx = 0f;  private float dy = 0f;  private float prevDx = 0f;  private float prevDy = 0f;  public ZoomLayout(Context context) {    super(context);    init(context);  }  public ZoomLayout(Context context, AttributeSet attrs) {    super(context, attrs);    init(context);  }  public ZoomLayout(Context context, AttributeSet attrs, int defStyle) {    super(context, attrs, defStyle);    init(context);  }  private void init(Context context) {    final ScaleGestureDetector scaleDetector = new ScaleGestureDetector(context, this);    this.setOnTouchListener(new View.OnTouchListener() {      @Override      public boolean onTouch(View view, MotionEvent motionEvent) {        switch (motionEvent.getAction() & MotionEvent.ACTION_MASK) {          case MotionEvent.ACTION_DOWN:            Log.i(TAG, "DOWN");            if (scale > MIN_ZOOM) {              mode = Mode.DRAG;              startX = motionEvent.getX() - prevDx;              startY = motionEvent.getY() - prevDy;            }            break;          case MotionEvent.ACTION_MOVE:            if (mode == Mode.DRAG) {              dx = motionEvent.getX() - startX;              dy = motionEvent.getY() - startY;            }            break;          case MotionEvent.ACTION_POINTER_DOWN:            mode = Mode.ZOOM;            break;          case MotionEvent.ACTION_POINTER_UP:            mode = Mode.DRAG;            break;          case MotionEvent.ACTION_UP:            Log.i(TAG, "UP");            mode = Mode.NONE;            prevDx = dx;            prevDy = dy;            break;        }        scaleDetector.onTouchEvent(motionEvent);        if ((mode == Mode.DRAG && scale >= MIN_ZOOM) || mode == Mode.ZOOM) {          getParent().requestDisallowInterceptTouchEvent(true);          float maxDx = (child().getWidth() - (child().getWidth() / scale)) / 2 * scale;          float maxDy = (child().getHeight() - (child().getHeight() / scale))/ 2 * scale;          dx = Math.min(Math.max(dx, -maxDx), maxDx);          dy = Math.min(Math.max(dy, -maxDy), maxDy);          Log.i(TAG, "Width: " + child().getWidth() + ", scale " + scale + ", dx " + dx            + ", max " + maxDx);          applyScaleAndTranslation();        }        return true;      }    });  }  // ScaleGestureDetector  @Override  public boolean onScaleBegin(ScaleGestureDetector scaleDetector) {    Log.i(TAG, "onScaleBegin");    return true;  }  @Override  public boolean onScale(ScaleGestureDetector scaleDetector) {    float scaleFactor = scaleDetector.getScaleFactor();    Log.i(TAG, "onScale" + scaleFactor);    if (lastScaleFactor == 0 || (Math.signum(scaleFactor) == Math.signum(lastScaleFactor))) {      scale *= scaleFactor;      scale = Math.max(MIN_ZOOM, Math.min(scale, MAX_ZOOM));      lastScaleFactor = scaleFactor;    } else {      lastScaleFactor = 0;    }    return true;  }  @Override  public void onScaleEnd(ScaleGestureDetector scaleDetector) {    Log.i(TAG, "onScaleEnd");  }  private void applyScaleAndTranslation() {    child().setScaleX(scale);    child().setScaleY(scale);    child().setTranslationX(dx);    child().setTranslationY(dy);  }  private View child() {    return getChildAt(0);  }}

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