<TextInput autoCapitalize={'none'} maxLength={10} placeholder='Mobile Number' value={this.state.mobile} onChangeText={(mobile) => this.onChanged(mobile)}/>
and onChanged method :
onChanged(text){
var newText = '';
var numbers = '0123456789';
if(text.length < 1){
this.setState({ mobile: '' });
}
for (var i=0; i < text.length; i++) {
if(numbers.indexOf(text[i]) > -1 ) {
newText = newText + text[i];
}
this.setState({ mobile: newText });
}
}