我是 Android 新手,懂一点 JAVA,但我想学习,我一直在做教程。我想要做的想法如下:我有一个渲染菜单,例如:1. BIRDS 2. ROCKS 3. PLANTS 当我按下 BIRDS 时,我想显示图片和一个小的描述。图片的 id 和我保存在 xml 中的描述。像这样:
<signs>
<sign id="1_1" category="1">
<name>desc1</name>
</sign>
<sign id="1_2" category="1">
<name>desc2</name>
</sign>
<sign id="1_3_1" category="1">
<name>desc3</name>
</sign>
<sign id="1_3_2" category="1">
<name>desc4</name>
</sign>
</signs>
图片在drawables中像sign_1_1.png,sign_1_2.png。
我制作了画廊,它正在展示,描述和图像也是可见的。我在图片库 Selected image 上进行了该操作,以在 TextView 中显示相应的描述。但是当我点击我得到一个致命的例外:
E/AndroidRuntime(22141): FATAL EXCEPTION: main
E/AndroidRuntime(22141): java.lang.NullPointerException
E/AndroidRuntime(22141): at apcmag.examples.singleSignListItem$ImageAdapter.getView(singleSignListItem.java:117)
E/AndroidRuntime(22141): at android.widget.Gallery.makeAndAddView(Gallery.java:849)
E/AndroidRuntime(22141): at android.widget.Gallery.fillToGalleryRightLtr(Gallery.java:803)
E/AndroidRuntime(22141): at android.widget.Gallery.fillToGalleryRight(Gallery.java:747)
E/AndroidRuntime(22141): at android.widget.Gallery.layout(Gallery.java:656)
E/AndroidRuntime(22141): at android.widget.Gallery.onLayout(Gallery.java:351)
E/AndroidRuntime(22141): at android.view.View.layout(View.java:13754)
E/AndroidRuntime(22141): at android.view.ViewGroup.layout(ViewGroup.java:4362)
代码是:
package apcmag.examples;
import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.AdapterView.OnItemSelectedListener;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.TextView;
import android.widget.Toast;
public class singleSignListItem extends Activity
{
public void onCreate(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
this.setContentView(R.layout.single_sign_gallery);
Gallery g = (Gallery) findViewById(R.id.gallery);
final Intent i = getIntent();
final String REGEX = "/%%/";
String product = i.getStringExtra("product");
setTitle(product);
g.setAdapter(new ImageAdapter(this));
g.setOnItemSelectedListener(new OnItemSelectedListener() {
public void onItemSelected(AdapterView<?> parent, View view, int position, long id)
{
String [] products = i.getStringExtra("product_text").split(REGEX);
Toast.makeText(singleSignListItem.this, ""+position, Toast.LENGTH_SHORT).show();
TextView show_intro = (TextView) findViewById(R.id.show_intro);
show_intro.setText(""+products[position]);
}
public void onNothingSelected(AdapterView<?> parent)
{
// TODO Auto-generated method stub
}
});
}
public class ImageAdapter extends BaseAdapter {
int mGalleryItemBackground;
private Context mContext;
// private Integer[] mImageIds = {
// R.drawable.sign_1_1,
// R.drawable.sign_1_1,
// R.drawable.sign_1_1,
// R.drawable.sign_1_1
// };
private Integer[] mImages = takePhotos();
public Integer[] takePhotos (){
Intent g = getIntent();
String Reg = "/%%/";
String Reg2 = "_%_";
String dataList = g.getStringExtra("product_text");
String [] datastring = dataList.split(Reg);
Integer[] imageResource = new Integer[20];
String[] dd = null;
for(int k = 0; k<datastring.length;k++){
dd = datastring[k].split(Reg2);
String imagename = "sign_"+dd[0];
imageResource[k] = getResources().getIdentifier(imagename, "drawable", getPackageName());
}
return imageResource;
}
public ImageAdapter(Context c) {
mContext = c;
TypedArray a = obtainStyledAttributes(R.styleable.HelloGallery);
mGalleryItemBackground = a.getResourceId(
R.styleable.HelloGallery_android_galleryItemBackground, 0);
a.recycle();
}
public int getCount() {
return mImages.length;
}
public Object getItem(int position) {
return position;
}
public long getItemId(int position) {
return position;
}
public View getView(int position, View convertView, ViewGroup parent) {
ImageView i = new ImageView(mContext);
i.setImageResource(mImages[position]);
i.setLayoutParams(new Gallery.LayoutParams(115, 200));
i.setScaleType(ImageView.ScaleType.FIT_XY);
i.setBackgroundResource(mGalleryItemBackground);
return i;
}
}
}
我几个小时都搞不清楚问题出在哪里,我有一些想法可能就在这里:
i.setLayoutParams(new Gallery.LayoutParams(115, 200));
但我不太确定该怎么做
更新
其实我发现了问题:
在第 77 行,我正在初始化大小为 20 的 ImageResource
Integer[] imageResource = new Integer[20];
但拆分后的数据字符串只有 4 个元素
String [] datastring = dataList.split(Reg);
所以 mImages 变量
private Integer[] mImages = takePhotos();
将有 20 个元素,其中 16 个为空,最后
i.setImageResource(mImages[position]);
它无法呈现空元素并且崩溃了。
所以我还有一个问题:
如果我不知道可能的 Integer[] 的大小,我该如何初始化并推入它的元素?与列表?