討論:如何在NDK中呼叫Java的class。本站提示廣大學習愛好者：（討論:如何在NDK中呼叫Java的class）文章只能為提供參考，不一定能成為您想要的結果。以下是討論:如何在NDK中呼叫Java的class正文
廢話不多說,直接上碼.......
package com.clouddevelop.cloudbox;
import android.graphics.Bitmap;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Paint.FontMetrics;
public class TextManager
{
public Bitmap create(String text, float size)
{
try
{
Paint paint = new Paint();
paint.setColor(Color.WHITE);
paint.setTextSize(size);
paint.setAlpha(255);
paint.setFlags(Paint.ANTI_ALIAS_FLAG);
paint.setTextAlign(Paint.Align.LEFT);
paint.setAntiAlias(true);
float[] widths = new float[text.length()];;
paint.getTextWidths(text, widths);
float width = 0;
for(int i = 0 ;i < widths.length ; i++)
width += widths[i];
FontMetrics fm = paint.getFontMetrics();
int mFontHeight = (int) (Math.ceil(fm.descent - fm.top) + 2);
Bitmap textImg = Bitmap.createBitmap((int)width, mFontHeight, Bitmap.Config.ARGB_8888);
Canvas c = new Canvas(textImg);
if(fm.ascent < 0)
c.drawText(text,0,(float)Math.abs(fm.ascent),paint);
else
c.drawText(text,0,fm.ascent* -1,paint);
return textImg;
}
catch (Exception e) { }
return null;
}
public int getWidth(Bitmap bmp) { return bmp.getWidth(); }
public int getHeight(Bitmap bmp) { return bmp.getHeight(); }
public void getPixels(Bitmap bmp, int[] pixels)
{
int w = bmp.getWidth();
int h = bmp.getHeight();
bmp.getPixels(pixels, 0, w, 0, 0, w, h);
}
public void close(Bitmap bmp)
{
bmp.recycle();
}
}
要在NDK中呼叫Java的類,第一步當然要有一個Java的類,這個類是我自行樹立
要發生一個文字的Bitmap,技術上沒什麼復雜性,樹立Paint,樹立Bitmap然後用Canvas將文字寫入
在Canvas的drawText中,會運用FontMetrics的值來寫入文字,所以應用fm.ascent讓文字往上對齊
// declare
JNIEXPORT void JNICALL Java_com_clouddevelop_cloudbox_CloudRenderer_nativeTextInit
(JNIEnv* env, jclass cls, jobject textManager);
// implement
JNIEXPORT void JNICALL Java_com_clouddevelop_cloudbox_CloudRenderer_nativeTextInit
(JNIEnv* env, jclass cls, jobject textManager)
{
g_env = env;
g_textmgr = textManager;
jclass business_class = env->GetObjectClass(g_textmgr);
AndroidLog("initial textmanager success!");
}
接上去要在JNI中將JNIEnv存到全域變量中g_env
jobject getInstance(JNIEnv* env, jclass obj_class)
{
jmethodID construction_id = env->GetMethodID(obj_class, "<init>", "()V");
jobject obj = env->NewObject(obj_class, construction_id);
return obj;
}
GLuint createText(const char* text, float size,float* rWidth, float* rHeight)
{
if(g_env)
AndroidLog("g_env exist");
if(g_textmgr)
AndroidLog("g_textmgr exist");
jclass order_class = g_env->FindClass("com/clouddevelop/cloudbox/TextManager");
AndroidLog("FindClass succeed");
g_textmgr = getInstance(g_env, order_class);
jclass cls = g_env->GetObjectClass(g_textmgr);
AndroidLog("get class succeed");
jmethodID mid;
mid = g_env->GetMethodID(cls, "create",
"(Ljava/lang/String;F)Landroid/graphics/Bitmap;");
AndroidLog("get create succeed");
jstring data = g_env->NewStringUTF(text);
jobject textImage = g_env->CallObjectMethod(g_textmgr, mid, data,size);
AndroidLog("call create succeed");
g_env->DeleteLocalRef(data);
g_env->NewGlobalRef(textImage);
/* Get image dimensions */
mid = g_env->GetMethodID(cls, "getWidth", "(Landroid/graphics/Bitmap;)I");
int width = g_env->CallIntMethod(g_textmgr, mid, textImage);
AndroidLog("call getWidth succeed");
mid = g_env->GetMethodID(cls, "getHeight", "(Landroid/graphics/Bitmap;)I");
int height = g_env->CallIntMethod(g_textmgr, mid, textImage);
AndroidLog("call getHeight succeed");
*rWidth = width;
*rHeight = height;
/* Get pixels */
jintArray image_data = g_env->NewIntArray(width * height);
g_env->NewGlobalRef(image_data);
mid = g_env->GetMethodID(cls, "getPixels", "(Landroid/graphics/Bitmap;[I)V");
g_env->CallVoidMethod(g_textmgr, mid, textImage, image_data);
AndroidLog("call getPixels succeed");
jint *pixels = g_env->GetIntArrayElements(image_data, 0);
//Now generate the OpenGL texture object
GLuint texture;
glGenTextures(1, &texture);
glBindTexture(GL_TEXTURE_2D, texture);
glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, width, height, 0, GL_RGBA,
GL_UNSIGNED_BYTE, (GLvoid*) pixels);
glTexParameteri(GL_TEXTURE_2D, GL_TEXTURE_MIN_FILTER, GL_NEAREST);
AndroidLog("generate texture succeed");
g_env->ReleaseIntArrayElements(image_data, pixels, 0);
g_env->DeleteGlobalRef(image_data);
/* Free image */
mid = g_env->GetMethodID(cls, "close", "(Landroid/graphics/Bitmap;)V");
g_env->CallVoidMethod(g_textmgr, mid, textImage);
AndroidLog("call close succeed");
g_env->DeleteGlobalRef(textImage);
return texture;
}
jobject getInstance(JNIEnv* env, jclass obj_class)
{
jmethodID construction_id = env->GetMethodID(obj_class, "<init>", "()V");
jobject obj = env->NewObject(obj_class, construction_id);
return obj;
}
下面這段代碼，是在native code中創立一個Java的實體類
這段代碼是我的CloudBox中創立文字紋理的代碼
mid = g_env->GetMethodID(cls, "getWidth", "(Landroid/graphics/Bitmap;)I");
int width = g_env->CallIntMethod(g_textmgr, mid, textImage);
其中這兩行,GetMethodID先獲得該類的辦法
在GetMethodID中第一參數是Java 類對象。第二個參數是參數（或辦法名），第三個參數是該參數（或辦法）的簽名。
那要如何獲得辦法的簽名呢？
我們要應用Javap -s TextManager這個指令來做
首先到.class所在的文件夾下，在我的范例中是在D:\CloudAndroid\CloudBox\CloudBoxAndroidGameApplication\bin\com\clouddevelop\cloudbox
然後鍵入javap -s TextManager就可以失掉了,Signature就是我們要的簽名。
辛勞了這麼久，我的CloudBox終於能顯示文字了！！！！！！
