[英]How to convert java CharSequence to c++ char* through JNI
I feel that this should have a simple answer as I can do it easily with a java String
, but something is going wrong with the CharSequence
. 我觉得这应该有一个简单的答案,因为我可以使用java
String
轻松完成此操作,但是CharSequence
出了点问题。 My java code initializes a cppGenerator
, passes a functionBlock object
to its generateImplementation method
, and returns a CharSequence
. 我的Java代码初始化
cppGenerator
,将functionBlock object
传递给它的generateImplementation method
,然后返回CharSequence
。 Here is my code: 这是我的代码:
jobject fBlock = env->CallObjectMethod(structuredTextModel, getFunction);
jclass CPPGenerator = lookForClass(env, "Path/CPPGenerator");
jobject CPPGeneratorImpl = invokeClassObj(env, CPPGenerator);
jmethodID generateImplementation = env->GetMethodID(CPPGenerator, "generateImplementation", "(LPath/FunctionBlock;)Ljava/lang/CharSequence;");
jobject mid = env->CallObjectMethod(CPPGeneratorImpl, generateImplementation, fBlock);
jstring jresult = (jstring)mid;
char* result = (char*)env->GetStringUTFChars(jresult, 0);
This logic has worked for me when using String
but this function returns a CharSequence
. 使用
String
时,此逻辑对我有用,但此函数返回CharSequence
。 No classes, objects, or methods are returning null. 没有类,对象或方法返回null。 The program crashes in
jni.h
attempting to call GetStringUTFChars
. 尝试调用
GetStringUTFChars
该程序在jni.h
崩溃。 So i know I cannot use this method for CharSequence. 所以我知道我不能对CharSequence使用此方法。 Is there just a jni method I am missing or do I have to do something completely different for a CharSequence?
我只是缺少一种jni方法,还是必须对CharSequence做完全不同的事情?
You can't just cast mid
to jstring
and call GetStringUTFChars
(since mid
might not be a String
, which seems to be the case). 您不能只将
mid
jstring
为jstring
并调用GetStringUTFChars
(因为mid
可能不是String
,这似乎是事实)。 There is no convenience method like GetStringUTFChars
for CharSequence
s like there is for String
s. 对于
CharSequence
没有像GetStringUTFChars
这样的便捷方法,就象String
。
You'd have to do it the inconvenient way of calling charAt
: 您必须以一种不方便的方式调用
charAt
:
jclass cCharSequence = env->FindClass("java/lang/CharSequence");
jmethodID mLength = env->GetMethodID(cCharSequence, "length", "()I");
jmethodID mCharAt = env->GetMethodID(cCharSequence, "charAt", "(I)C");
int length = env->CallIntMethod(mid, mLength);
std::string str;
str.reserve(length);
for(int i = 0; i < length; i++) {
str += env->CallCharMethod(mid, mCharAt, i);
}
// use 'str.c_str()'...
Why not use toString
directly? 为什么不直接使用
toString
?
jclass clzCharSequence = env->GetObjectClass(mid);
jmethodID toString = env->GetMethodID(clzCharSequence, "toString", "()Ljava/lang/String;");
jobject s = env->CallObjectMethod(mid, toString);
const char* cstr = env->GetStringUTFChars(static_cast<jstring>(s), NULL);
// do something with cstr
env->ReleaseStringUTFChars(static_cast<jstring>(s), cstr);
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