React-Native : measure a View

问题:

I'm trying to measure a view using a ref, but the width returned is 0 despite the fact that I see the view displayed on the screen (and it's far from being equal to 0).

I tried to follow this : https://github.com/facebook/react-native/issues/953 but it just doesn't work ... I just want to get the actual width of the View.

Here is my code :

var Time = React.createClass({
  getInitialState: function() {
    return({ progressMaxSize: 0 }); 
  },
  componentDidMount: function() {
    this.measureProgressBar();
  },
  measureProgressBar: function() {
    this.refs.progressBar.measure(this.setWidthProgressMaxSize);
  },
  setWidthProgressMaxSize: function(ox, oy, width, height, px, py) {
    this.setState({ progressMaxSize: width });
  },
  render: function() {
    return(
      <View style={listViewStyle.time} ref="progressBar">
        <View style={listViewStyle.progressBar} >
          <View style={[listViewStyle.progressMax, { width: this.state.progressMaxSize }]}/>
        </View>
      </View>
    );
  }
}); 

The styles associated :

time: {
    position: 'absolute',
    bottom: 5,
    left: 5,
    right: 5,
    backgroundColor: '#325436',
    flexDirection: 'row',
  },
  progressBar: {
    flex: 1,
    backgroundColor: '#0000AA',
  },
  progressMax: {
    position: 'absolute',
    top: 0,
    left: 0,
    backgroundColor: '#000',
    height: 30, 
  },

回答1:

You want to measure the progress bar onLayout.

var Time = React.createClass({
  getInitialState: function() {
    return({ progressMaxSize: 0 }); 
  },
  measureProgressBar: function() {
    this.progressBar.measure(this.setWidthProgressMaxSize);
  },
  setWidthProgressMaxSize: function(ox, oy, width, height, px, py) {
    this.setState({ progressMaxSize: width });
  },
  render: function() {
    return(
      <View style={listViewStyle.time} ref={(c) => { this.progressBar = c; } onLayout={this.measureProgressBar}>
        <View style={listViewStyle.progressBar} >
          <View style={[listViewStyle.progressMax, { width: this.state.progressMaxSize }]}/>
        </View>
      </View>
    );
  }
});

回答2:

To measure view size, no need to use ref at all. You can get it from nativeEvent passed by onLayout.

measureView(event: Object) {
   console.log(`*** event: ${JSON.stringify(event.nativeEvent)}`);
   // you'll get something like this here:
   // {"target":1105,"layout":{"y":0,"width":256,"x":32,"height":54.5}}
}

render() {
    return (
        <View onLayout={(event) => {this.measureView(event)}} />
    );
}

回答3:

During the night some guys talked about a (hacky) solution but it solved my problem, found it here: https://github.com/facebook/react-native/issues/953

Basically the solution is to use setTimeout and everything just works magically:

componentDidMount: function() {
  setTimeout(this.measureProgressBar);
},

measureProgressBar: function() {
  this.refs.progressBar.measure((a, b, width, height, px, py) =>
    this.setState({ progressMaxSize: width })
  );
}