英文:
getConstants in React native
问题
我正在尝试学习React Native中的原生开发。
我正在阅读React Native文档，上面写着：
一个可选的方法叫做
getConstants，它返回暴露给JavaScript的常量值。虽然不需要实现它，但用于将需要从JavaScript同步到Java的预定义键值有效地传递非常有用。
具有以下代码片段：
@Override
public Map<String, Object> getConstants() {
final Map<String, Object> constants = new HashMap<>();
constants.put(DURATION_SHORT_KEY, Toast.LENGTH_SHORT);
constants.put(DURATION_LONG_KEY, Toast.LENGTH_LONG);
return constants;
}
通过上述定义，我能理解这是将常量信息从JavaScript传递到Java（例如API密钥）的一次性传递。
为了确认，我访问了react-native-maps仓库。
在那里，我看到它们像这样使用：
@Override
public Map<String, Object> getConstants() {
final Map<String, Object> constants = new HashMap<>();
constants.put("legalNotice", "This license information is displayed in Settings > Google > Open Source on any device running Google Play services.");
return constants;
}
并且它没有使用传递的任何内容。
所以，有人可以解释一下上面的定义稍微详细一些吗？getConstants()方法有什么用途？
英文:
I am trying to learn native development in React Native
I was going through React Native docs and it says
> An optional method called getConstants returns the constant values
> exposed to JavaScript. Its implementation is not required but is very
> useful to key pre-defined values that need to be communicated from
> JavaScript to Java in sync
with following snippet
@Override
public Map<String, Object> getConstants() {
final Map<String, Object> constants = new HashMap<>();
constants.put(DURATION_SHORT_KEY, Toast.LENGTH_SHORT);
constants.put(DURATION_LONG_KEY, Toast.LENGTH_LONG);
return constants;
}
From the above defination, I was able to make out that this pass constant one time use information from Javascript to java (such as api key)
To confirm, I went to react-native-maps repo.
There I saw they have used it like this
@Override
public Map<String, Object> getConstants() {
final Map<String, Object> constants = new HashMap<>();
constants.put("legalNotice", "This license information is displayed in Settings > Google > Open Source on any device running Google Play services.");
return constants;
}
and it isn't consuming anything passed.
So can someone please explain me the above definition in slightly more details? and what is it use (getConstants() method)?
答案1
得分: 0
getConstants 定义了在 JavaScript 环境中可供使用的常量。在希望让 JavaScript 指定某些参数时非常有用。
来自 React Native 文档的示例：
@ReactMethod
public void show(String message, int duration) {
Toast.makeText(getReactApplicationContext(), message, duration).show();
}
@Override
public Map<String, Object> getConstants() {
final Map<String, Object> constants = new HashMap<>();
constants.put("SHORT", Toast.LENGTH_SHORT);
constants.put("LONG", Toast.LENGTH_LONG);
return constants;
}
这将创建一个名为 SHORT 的常量，其值为 Toast.LENGTH_SHORT（整数）。因此，在 JavaScript 端，它们可以像这样使用该常量：
ToastModule.show('message', ToastModule.SHORT);
这样，JavaScript 不需要知道 Toast.LENGTH_SHORT 的实际整数值，而是使用由原生模块（ToastExample.SHORT）暴露的常量。
英文:
getConstants defines constant that can be consumed in JavaScript world. It is useful when you want to let JavaScript specify some parameters.
Example from react native doc:
@ReactMethod
public void show(String message, int duration) {
Toast.makeText(getReactApplicationContext(), message, duration).show();
}
@Override
public Map<String, Object> getConstants() {
final Map<String, Object> constants = new HashMap<>();
constants.put("SHORT", Toast.LENGTH_SHORT);
constants.put("LONG", Toast.LENGTH_LONG);
return constants;
}
This will create a constant SHORT with value of Toast.LENGTH_SHORT (integer). so on JavaScript side they can use the constant like
ToastModule.show('message', ToastModule.SHORT);
This way JavaScript doesn't have to know actual integer value of Toast.LENGTH_SHORT and instead use the constant exposed by native module (ToastExample.SHORT).
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