问题

Here is the translated portion of the text you provided:

当我将函数传递给onPress时，它从不被触发，只有当从子组件传递了对主组件中的函数的引用时才会触发。同时，即使我在TextInput中输入值，它也返回没有值的警报。任何帮助将不胜感激。

例如，当我直接将props.onPress传递给onPress时，它被触发并调用引用函数。

<Button title='Add Goal' onPress={props.onPress} /> // 正常工作

但是，当我声明一个函数并将该函数传递给onPress时，onPress就像上面那样永远不会被触发。

以下是完整的代码：

function LoginKey(props) {
  const [enteredApiKey, setEnteredKey] = useState('');

  function keyInputHandler(enteredKey) {
    setEnteredKey(enteredApiKey);
  }

  function Press() {
    if (enteredApiKey.length === 0) {
      Alert.alert('请输入一个值');
    } else {
      props.onPress();
    }
  }

  return (
    <Modal visible={props.visible} animationType='slide'>
      <View style={styles.inputContainer}>
        <Image
          style={styles.image}
          source={require('../assets/Image/ucp.png')}
        />
        <TextInput
          style={styles.textInput}
          placeholder='输入 API 密钥！'
          onChangeText={keyInputHandler}
        />
        <View style={styles.buttonContainer}>
          <Button title='Add Goal' onPress={Press} /> {/* 不起作用 */}
          <Button title='Add Goal' onPress={props.onPress} /> {/* 起作用 */}
        </View>
      </View>
    </Modal>
  );
}

希望这有所帮助。

英文:

when I pass function to onPress it never gets fired and it only fires when the props with reference function from main component is passed from child component. AT the same time even if I enter value for usestate inside TextInput ,it returns Alert with no value. Any hep would he highly appreciated.

eg when I passed props.onPress directly to onPress, it gets fired and calls reference function.

  &lt;Button title=&#39;Add Goal&#39; onPress={props.onPress} /&gt; //WORKS 



function Press() {
if(enteredApiKey.length()==&quot;&quot;){
  Alert.alert(&quot;enter a value &quot;);
  
}
else {
   props.onPress;
}

   
   }

 &lt;Button title=&#39;Add Goal&#39; onPress={Press} /&gt;.  // NOT WORKING

but when I declare a function and pass that function to onPress , onPress never gets fired as above

Entire code is as below

function LoginKey(props) {
  const [enteredApiKey, setEnteredKey] = useState(&#39;&#39;);

  function keyInputHandler(enteredKey) {
    setEnteredKey(enteredApiKey);
  }

  function Press() {
if(enteredApiKey.length()==&quot;&quot;){
  Alert.alert(&quot;enter a value &quot;);
  
}
else {
   props.onPress;
}

  

  return (
    &lt;Modal visible={props.visible} animationType=&#39;slide&#39;&gt;
      &lt;View style={styles.inputContainer}&gt;
        &lt;Image
          style={styles.image}
          source={require(&#39;../assets/Image/ucp.png&#39;)}
        /&gt;
        &lt;TextInput
          style={styles.textInput}
          placeholder=&#39;Enter Api key !&#39;
          onChangeText={keyInputHandler}
        /&gt;
        &lt;View style={styles.buttonContainer}&gt;

        &lt;Button title=&#39;Add Goal&#39; onPress={Press} /&gt;       // does not works 
        &lt;Button title=&#39;Add Goal&#39; onPress={props.onPress} /&gt;.    //works 



        &lt;/View&gt;
      &lt;/View&gt;
    &lt;/Modal&gt;
  );