通过JNI调用简单的Java静态方法是行不通的，虽然C ++编译和运行它 [英] Calling simple java static method via JNI does not work, though c++ compiles and run it

问题描述

考虑使用静态方法这个Java类：

Considering this Java class with the static method:

public class TestClass{
    public string str;
    public TestClass() {
        str = "Test From Java";
    }
    public static String staticMethod() {
        return "Test From Java";
    }
}

我已经用C写code的这些行++文件：

I have written these lines of code in c++ file:

QAndroidJniObject str =  QAndroidJniObject::callStaticObjectMethod(
                                   "org/.../TestClass"
                                   ,"staticMethod"
                                   ,"(V)Ljava/lang/String;");

似乎一切正常，但我不知道我怎么可以使用 STR 对象。我试图将其转换为使用 str.tostring（）方法的的QString 对象，但它总是返回一个空字符串。
为什么预期它不工作？我还测试了（）Ljava /朗/字符串;！的方法签名，但没有成功，结果
先谢谢了。

It seems everything is working but I don't know how can I use the str Object. I tried to convert it to a QString object using str.tostring() method but it always returns an empty string. Why it does not work as expected? I've also tested ()Ljava/lang/String; for method signature but no success!
Thanks in advance.

推荐答案

您应该指定返回JNI类型＆LT; ...＆GT;调用方法时：

You should specify the returned JNI type in <...> when calling the method :

QAndroidJniObject str =  QAndroidJniObject::callStaticObjectMethod<jstring>(
                               "org/.../TestClass"
                               ,"staticMethod");

QString string = str.toString();

下面有没有必要定义签名，因为你的函数没有参数。

Here there is no need to define the signature since your function has no argument.

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