Question

当用户用两根手指捏住图像时，我想放大或缩小图像。如何使用PanResponder来实现它？

或者有人可以建议我如何做一个好的逻辑吗？

PS：我不想使用任何外部API。

Answer 1

对于ios，它可以将图像包装在ScrollView中，因为它具有对以下属性的内置支持

maximumZoomScale
minimumZoomScale
pinchGestureEnabled

尝试类似

<ScrollView 
      maximumZoomScale={SOME_VALUE i.e. 2.5}
      minimumZoomScale={MIN_ZOOM_VALUE i.e 1.0}
      pinchGestureEnabled={true}
>
       <Image source={YOUR_IMAGE} style={YOUR_IMAGE_STYLEs}/>
</Scrollview>

在Android上，您可能需要使用某些库或通过PanResponder和Animated对其进行管理，PanResponder示例代码可能是您的一个很好的起点。

class ExampleComponent extends Component {
  constructor(props) {
    super(props);
    this._panResponder = PanResponder.create({
      // Ask to be the responder:
      onStartShouldSetPanResponder: (evt, gestureState) => true,
      onStartShouldSetPanResponderCapture: (evt, gestureState) => true,
      onMoveShouldSetPanResponder: (evt, gestureState) => true,
      onMoveShouldSetPanResponderCapture: (evt, gestureState) => true,

      onPanResponderGrant: (evt, gestureState) => {
        // The gesture has started. Show visual feedback so the user knows
        // what is happening!
        // gestureState.d{x,y} will be set to zero now
      },
      onPanResponderMove: (evt, gestureState) => {
        // The most recent move distance is gestureState.move{X,Y}
        // The accumulated gesture distance since becoming responder is
        // gestureState.d{x,y}
      },
      onPanResponderTerminationRequest: (evt, gestureState) => true,
      onPanResponderRelease: (evt, gestureState) => {
        // The user has released all touches while this view is the
        // responder. This typically means a gesture has succeeded
      },
      onPanResponderTerminate: (evt, gestureState) => {
        // Another component has become the responder, so this gesture
        // should be cancelled
      },
      onShouldBlockNativeResponder: (evt, gestureState) => {
        // Returns whether this component should block native components from becoming the JS
        // responder. Returns true by default. Is currently only supported on android.
        return true;
      },
    });
  }

  render() {
    const imageStyles = {transform: [
  {
    scale: ANIMATION_VALUE_CALCULATED_ON_MOVEMENT //
  }
]}
    return <Animated.Image {...this._panResponder.panHandlers} style ={imageStyles} source={IMAGE_SOURCE}/>;
  }
}

如何使用PanResponder在React Native中缩放图像？

1 个答案: