Objective-C basics for Web Developers

Project Starter Files / Structure

When you start a project you'll start with the following:

AppDelegate.h
AppDelegate.m

ViewController.h
ViewController.m

Everything in the AppDelegate is Global. Any View the user is currently in will have access to the logic inside the AppDelegate.

And together these ViewController.* and AppDelegate.* files create the AppDelegate Class.

Notice how you have an AppDelegate.h as well as another one with a “.m” extension.

Header Files (Files With .h Extensions)

These are called the Header Files. Everything in here is Public.

complies all .c and .m files and replaces any #include *, or #import * directives with the entire text of those files where that directive #include *, or #import * statement was.

Example

---

Assume you have the following: Example.c

Alice
#include "Example.h"
Wonderland

Example.h

in

Compiled Result

Alice
in
Wonderland

Whats Happening The compiler would, after processing the replaces any #include *, or #import * directives with the entire compiled outout would show:

Implementation Files (Files With .m Extensions)

Is called the Implementation Files (where the .m I assume stands for "Model", seeing as Objective-C uses the MV Architecture), Everything in here is Private. It's public when it's methods are included in the .h header file.

These are where your logic goes.

Syntax

Example using NSLog

NSLog

notice:

1. NSLog(@"My Log %@")

%@

Is a Placeholder for Objects but NSString and NSNumber are both classes, and emit object instances of themselves when we create pointers with them

Defining A String:

You're not supposed to use int, string, const, or char's in Objective-C

1| NSLog(@"My Log %@")
2| NSString *myString = @"Hello World"
      ^        ^            ^
      |        |            |
  Definition   |      `@` says its a string
               |
         A Pointer You Created

Lets that exand that by adding a number

1| NSLog(@"My Log %@")
2| NSString *myString = @"Hello World"
3| NSNumber *myNumber = [NSNumber numberWithInt:420]
      ^        ^            ^
      |        |            |
  Definition   |      * See Below
               |
         A Pointer You Created
4| NSLog(@"My Log: %@",myString)
output >> "My Log: Hello World"

Notice the scary

[NSNumber numberWithInt:420]

All this is saying is

[<CLASS> <CLASS METHOD>:<PARAM>]

Where you use the [] brackets to call a method of a class.

Now lets log both our numbers and strings

1| //NSLog(@"My Log %@")
2| NSString *myString = @"Hello World"
3| NSNumber *myNumber = [NSNumber numberWithInt:420]
4| NSLog(@"%@ let's %@ it up in here", myString, myNumber)
output >> "Hello World let's 420 it up in here"

Importing And Exporting

Include

For C and C++ Files

Import

For Objective-C Files

Terminology

Interface

A Skeleton or Schema to create Objects or Arrays

Take the follwing

1| @interface Person : NSObject{
2|      NSString *name
3| }

Instance Variables: Anything inside the @interface's {}s

To Create an Instance Method do it outside the @interface's {}s Instance Methods use -(void):

1| @interface Person : NSObject{
2|      NSString *name
3| }
4| -(void)

Class Variables use +(void):

1| @interface Person : NSObject{
2|      NSString *name
3| }
4| +(void)

Resources

• .h & .m Extensions - http://stackoverflow.com/a/2620632/4642530 Advanced Objective-C basics for Expericnced Programers - https://www.youtube.com/watch?v=jztMdaFV90U

Lets start with boiler template

/* @flow */

import React, { Component } from 'react';
import {
  View,
  TouchableOpacity,
  Text,
  StyleSheet,
  PanResponder,
} from 'react-native';



export default class PanResponderDemo extends Component {
state={
  debugActions:"Not Touched",
  actions:[" ------------- Start ------------- "]
}
  componentWillMount(){
  this._panResponder = PanResponder.create({
    // Ask to be the responder:
    onStartShouldSetPanResponder: (evt, gestureState) => {
      this.setState({actions: this.state.actions.concat("1) onStartShouldSetPanResponder")})
      // return true

    },
    onStartShouldSetPanResponderCapture: (evt, gestureState) => {
      this.setState({actions: this.state.actions.concat("2) onStartShouldSetPanResponderCapture")})
      // return true

    },
    onMoveShouldSetPanResponder: (evt, gestureState) => {
      this.setState({debugActions:"3) onMoveShouldSetPanResponder"})
      // return true
    },
    onMoveShouldSetPanResponderCapture: (evt, gestureState) => {
      this.setState({actions: this.state.actions.concat("4) onMoveShouldSetPanResponderCapture")})
      // return 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) => {
      this.setState({actions: this.state.actions.concat("6) onPanResponderMove")})


      // 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) => {
      this.setState({actions: this.state.actions.concat("7) onPanResponderRelease")})


      // The user has released all touches while this view is the
      // responder. This typically means a gesture has succeeded
    },
    onPanResponderTerminate: (evt, gestureState) => {
      this.setState({actions: this.state.actions.concat("8) onPanResponderTerminate")})


      // Another component has become the responder, so this gesture
      // should be cancelled
    },
    onShouldBlockNativeResponder: (evt, gestureState) => {
      this.setState({actions: this.state.actions.concat("9) onShouldBlockNativeResponder")})


      // 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() {
    let {actions} = this.state

    if(this.state.actions.length>20){
      this.state.actions.shift()
      this.setState({actions: this.state.actions});
    }

    return (
      <View style={s.container}>
        {/* Pan Responder Item */}
        <View style={[s.panItem,]}{...this._panResponder.panHandlers}>
        </View>







        {/* DEBUG FLOATING CONTAINER */}
        <TouchableOpacity onPress={()=>this.setState({actions:[" ------------- Restarted ------------- "]})} style={[{},s.debugContainer]}>
          {this.state.actions.map((o,i)=>{
            return <Text key={i} style={s.debugActions}>{o}</Text>
          })}
        </TouchableOpacity>

      </View>
    );
  }
}

const s = StyleSheet.create({
  container: {
    flex: 1,
    justifyContent:"center",alignItems:"center",
  },
  panItem: {
    backgroundColor:"red",
    height:50,
    width:50,
  },
  debugContainer:{
    position:"absolute",
    bottom:25,
    right:10,
    flex:1,
    zIndex:3,
    width:null,
    height:null,
    alignItems:"center",
    justifyContent:"center",
    backgroundColor:"rgba(0,0,0,.5)"
  },
  debugActions:{
    fontSize: 10,
    color:"white",
    textAlign: "center",
    margin: 0,
  },
});

Im referring to each PanResponder Function by Numbers as they are long function names:

1. onStartShouldSetPanResponder
2. onStartShouldSetPanResponderCapture
3. onMoveShouldSetPanResponderCapture
4. onPanResponderMove
5. onPanResponderRelease
6. onPanResponderTerminate
7. onShouldBlockNativeResponder

(URL to Imgur Album - http://imgur.com/a/F6abq) Lets first make some observations. Here I have 1,2,3 & 4 returning false

Open in Imgur (New Tab) - https://i.imgur.com/escV7Ol.gif

Result: only calls 1 & 4 when touched

Now Lets make them (1,2,3 & 4) return true

Open in Imgur (New Tab) - http://i.imgur.com/t3aAGRK.gif

Result: calls 1,5,6,8,7 when touched