[DatePicker] Can't reset date

[MihaMarkic]

Problem description

Using DatePicker user can't reset the date once it is set. It could be solved by allowing typing of the date (I see it is a separate request) or with a button either on input field or dialog.

Link to minimally-working code that reproduces the issue

Versions

• Material-UI: 0.16.4
• React: 15.4.1
• Browser: any

[linonetwo]

Use controlled component

              <DatePicker
                className={styles.date}
                hintText="终止日期"
                container="inline"
                value={this.state.filter.toTime}
                onDismiss={() => this.toTimeHandler(null, null, true)}
                onChange={this.toTimeHandler}
              />

  toTimeHandler = (event, date, cancel) => {
    const nextState = Object.assign({}, this.state);
    if (!cancel) {
      nextState.filter.toTime = date;
    } else {
      nextState.filter.toTime = null;
    }
    this.setState(nextState);
  };

[oliviertassinari]

Closing for #4787