android中如何处理空指针异常
我正在尝试创建照片库应用程序。但我有以下错误,我的程序将崩溃。我的这行代码也有错误:android中如何处理空指针异常,android,Android,我正在尝试创建照片库应用程序。但我有以下错误,我的程序将崩溃。我的这行代码也有错误: imageView.setImageResource(pics[arg2]); 错误 这是我的密码: package com.sai.samples.views; import android.app.Activity; import android.content.Context; import android.content.res.TypedArray; import android.os.Bundl
imageView.setImageResource(pics[arg2]);
错误
这是我的密码:
package com.sai.samples.views;
import android.app.Activity;
import android.content.Context;
import android.content.res.TypedArray;
import android.os.Bundle;
import android.view.View;
import android.view.ViewGroup;
import android.widget.AdapterView;
import android.widget.BaseAdapter;
import android.widget.Gallery;
import android.widget.ImageView;
import android.widget.Toast;
import android.widget.AdapterView.OnItemClickListener;
public class GalleryView extends Activity {
Integer[] pics = {
R.drawable.antartica1,
R.drawable.antartica2,
R.drawable.antartica3,
R.drawable.antartica4,
R.drawable.antartica5,
R.drawable.antartica6,
R.drawable.antartica7,
R.drawable.antartica8,
R.drawable.antartica9,
R.drawable.antartica10
};
ImageView imageView;
/** Called when the activity is first created. */
@Override
public void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
Gallery ga = (Gallery)findViewById(R.id.Gallery01);
ga.setAdapter(new ImageAdapter(this));
imageView = (ImageView)findViewById(R.id.ImageView01);
ga.setOnItemClickListener(new OnItemClickListener() {
@Override
public void onItemClick(AdapterView<?> arg0, View arg1, int arg2,
long arg3) {
Toast.makeText(getBaseContext(),
"You have selected picture " + (arg2+1) + " of Antartica",
Toast.LENGTH_SHORT).show();
imageView.setImageResource(pics[arg2]);
}
});
}
public class ImageAdapter extends BaseAdapter {
private Context ctx;
int imageBackground;
public ImageAdapter(Context c) {
ctx = c;
TypedArray ta = obtainStyledAttributes(R.styleable.Gallery1);
imageBackground = ta.getResourceId(R.styleable.Gallery1_android_galleryItemBackground, 1);
ta.recycle();
}
@Override
public int getCount() {
return pics.length;
}
@Override
public Object getItem(int arg0) {
return arg0;
}
@Override
public long getItemId(int arg0) {
return arg0;
}
@Override
public View getView(int arg0, View arg1, ViewGroup arg2) {
ImageView iv = new ImageView(ctx);
iv.setImageResource(pics[arg0]);
iv.setScaleType(ImageView.ScaleType.FIT_XY);
iv.setLayoutParams(new Gallery.LayoutParams(150,120));
iv.setBackgroundResource(imageBackground);
return iv;
}
}
}
package com.sai.samples.views;
导入android.app.Activity;
导入android.content.Context;
导入android.content.res.TypedArray;
导入android.os.Bundle;
导入android.view.view;
导入android.view.ViewGroup;
导入android.widget.AdapterView;
导入android.widget.BaseAdapter;
导入android.widget.Gallery;
导入android.widget.ImageView;
导入android.widget.Toast;
导入android.widget.AdapterView.OnItemClickListener;
公共类GalleryView扩展活动{
整数[]pics={
R.drawable.antartica1,
R.drawable.antartica2,
R.drawable.antartica3,
R.drawable.antartica4,
R.drawable.antartica5,
R.drawable.antartica6,
R.drawable.antartica7,
R.drawable.antartica8,
R.drawable.antartica9,
R.可牵引的
};
图像视图图像视图;
/**在首次创建活动时调用*/
@凌驾
创建时的公共void(Bundle savedInstanceState){
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
画廊ga=(画廊)findViewById(R.id.Gallery01);
ga.setAdapter(新的ImageAdapter(this));
imageView=(imageView)findViewById(R.id.ImageView01);
ga.setOnItemClickListener(新的OnItemClickListener(){
@凌驾
公共链接(AdapterView arg0、视图arg1、内部arg2、,
长arg3){
Toast.makeText(getBaseContext(),
“您已选择Antartica的图片”+(arg2+1)+”,
吐司。长度(短)。show();
setImageResource(pics[arg2]);
}
});
}
公共类ImageAdapter扩展了BaseAdapter{
私有上下文ctx;
int图像背景;
公共图像适配器(上下文c){
ctx=c;
TypedArray ta=获得的StyledAttributes(R.styleable.Gallery1);
imageBackground=ta.getResourceId(R.styleable.Gallery1\u android\u galleryItemBackground,1);
ta.recycle();
}
@凌驾
public int getCount(){
返回图片长度;
}
@凌驾
公共对象getItem(int arg0){
返回arg0;
}
@凌驾
公共长getItemId(int arg0){
返回arg0;
}
@凌驾
公共视图getView(int arg0、视图arg1、视图组arg2){
ImageView iv=新的ImageView(ctx);
iv.setImageResource(pics[arg0]);
iv.setScaleType(ImageView.ScaleType.FIT_XY);
iv.设置布局参数(新画廊布局参数(150120));
iv.挫折背景资源(图像背景);
回报四;
}
}
}
这是我的main.xml
<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent">
<Gallery
android:id="@+id/Gallery01"
android:layout_width="fill_parent"
android:layout_height="wrap_content"></Gallery>
<ImageView
android:id="@+id/ImageView01"
android:layout_width="wrap_content"
android:layout_height="wrap_content"></ImageView>
</LinearLayout>
此行可能返回空值:
imageView = (ImageView)findViewById(R.id.ImageView01);
检查
ImageView
id是否正确,如果错误仍然存在,请尝试清理并重建项目。我已使用此代码创建图像库
public class GalleryViewActivity extends Activity
{
GridView gridView;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
gridView = (GridView)findViewById(R.id.gridView);
gridView.setAdapter(new ImageAdapter(this));
}
}
class ImageAdapter extends BaseAdapter
{
ArrayList<String> images;
private Context mContext;
public ImageAdapter(Context c)
{
mContext = c;
}
public int getCount()
{
return mThumbIds.length;
}
public Object getItem(int position)
{
return null;
}
public long getItemId(int position)
{
return 0;
}
// create a new ImageView for each item referenced by the Adapter
public View getView(final int position, View convertView, ViewGroup parent)
{
ImageView imageView;
if (convertView == null)
{ // if it's not recycled, initialize some attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
}
else
{
imageView = (ImageView) convertView;
}
imageView.setClickable(true);
imageView.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
Intent i = new Intent(v.getContext(), showImageClass.class);
Toast.makeText(v.getContext(), mThumbIds.toString() + " Clicked", 5000).show();
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
i.putExtra("imageName", mThumbIds[position]);
v.getContext().startActivity(i);
}
});
// imageView.setImageDrawable(images);
// imageView.setImageBitmap(images);
// imageView.setImageResource(images[]);
imageView.setImageResource(mThumbIds[position]);
return imageView;
}
// references to images
private Integer[] mThumbIds =
{
R.drawable.abc,
R.drawable.def,
R.drawable.klm,
R.drawable.pqr,
R.drawable.rst,
R.drawable.wxy,
R.drawable.xyz,
};
}
公共类GalleryViewActivity扩展活动
{
GridView;
@凌驾
创建时的公共void(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
gridView=(gridView)findViewById(R.id.gridView);
setAdapter(新的ImageAdapter(this));
}
}
类ImageAdapter扩展BaseAdapter
{
阵列图像;
私有上下文;
公共图像适配器(上下文c)
{
mContext=c;
}
public int getCount()
{
返回mThumbIds.length;
}
公共对象getItem(int位置)
{
返回null;
}
公共长getItemId(int位置)
{
返回0;
}
//为适配器引用的每个项目创建新的ImageView
公共视图getView(最终整数位置、视图转换视图、视图组父视图)
{
图像视图图像视图;
if(convertView==null)
{//如果没有回收,初始化一些属性
imageView=新的imageView(mContext);
setLayoutParams(新的GridView.LayoutParams(85,85));
imageView.setScaleType(imageView.ScaleType.CENTER\U裁剪);
设置填充(8,8,8,8);
}
其他的
{
imageView=(imageView)convertView;
}
imageView.setClickable(真);
setOnClickListener(新的OnClickListener()
{
@凌驾
公共void onClick(视图v)
{
Intent i=新的Intent(v.getContext(),showImageClass.class);
Toast.makeText(v.getContext(),mThumbIds.toString()+“单击”,5000.show();
i、 设置标志(意图、标志、活动、新任务);
i、 putExtra(“imageName”,mThumbIds[位置]);
v、 getContext().startActivity(i);
}
});
//imageView.setImageDrawable(图像);
//设置图像位图(图像);
//setImageResource(images[]);
setImageResource(mThumbIds[position]);
返回图像视图;
}
//对图像的引用
私有整数[]mThumbIds=
{
R.drawable.abc,
R.drawable.def,
荷兰皇家航空公司,
R.drawable.pqr,
R.drawable.rst,
R.drawable.wxy,
R.drawable.xyz,
};
}
首先创建GalleryViewActivity类
public class GalleryViewActivity extends Activity
{
GridView gridView;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
gridView = (GridView)findViewById(R.id.gridView);
gridView.setAdapter(new ImageAdapter(this));
}
}
class ImageAdapter extends BaseAdapter
{
ArrayList<String> images;
private Context mContext;
public ImageAdapter(Context c)
{
mContext = c;
}
public int getCount()
{
return mThumbIds.length;
}
public Object getItem(int position)
{
return null;
}
public long getItemId(int position)
{
return 0;
}
// create a new ImageView for each item referenced by the Adapter
public View getView(final int position, View convertView, ViewGroup parent)
{
ImageView imageView;
if (convertView == null)
{ // if it's not recycled, initialize some attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
}
else
{
imageView = (ImageView) convertView;
}
imageView.setClickable(true);
imageView.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
Intent i = new Intent(v.getContext(), showImageClass.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
i.putExtra("position", "" + position);
v.getContext().startActivity(i);
}
});
imageView.setImageResource(mThumbIds[position]);
return imageView;
}
// references to images
private Integer[] mThumbIds =
{
R.drawable.abc,
R.drawable.def,
R.drawable.klm,
R.drawable.pqr,
R.drawable.rst,
R.drawable.wxy,
R.drawable.xyz,
};
}
这个代码对我来说很有用,它肯定会有用的。。
别忘了添加相关的图像并导入所需的类库。
请在android清单文件中提及这两项活动
public class GalleryViewActivity extends Activity
{
GridView gridView;
@Override
public void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.main);
gridView = (GridView)findViewById(R.id.gridView);
gridView.setAdapter(new ImageAdapter(this));
}
}
class ImageAdapter extends BaseAdapter
{
ArrayList<String> images;
private Context mContext;
public ImageAdapter(Context c)
{
mContext = c;
}
public int getCount()
{
return mThumbIds.length;
}
public Object getItem(int position)
{
return null;
}
public long getItemId(int position)
{
return 0;
}
// create a new ImageView for each item referenced by the Adapter
public View getView(final int position, View convertView, ViewGroup parent)
{
ImageView imageView;
if (convertView == null)
{ // if it's not recycled, initialize some attributes
imageView = new ImageView(mContext);
imageView.setLayoutParams(new GridView.LayoutParams(85, 85));
imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
imageView.setPadding(8, 8, 8, 8);
}
else
{
imageView = (ImageView) convertView;
}
imageView.setClickable(true);
imageView.setOnClickListener(new OnClickListener()
{
@Override
public void onClick(View v)
{
Intent i = new Intent(v.getContext(), showImageClass.class);
i.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
i.putExtra("position", "" + position);
v.getContext().startActivity(i);
}
});
imageView.setImageResource(mThumbIds[position]);
return imageView;
}
// references to images
private Integer[] mThumbIds =
{
R.drawable.abc,
R.drawable.def,
R.drawable.klm,
R.drawable.pqr,
R.drawable.rst,
R.drawable.wxy,
R.drawable.xyz,
};
}
public class showImageClass extends Activity
{
private Integer[] mThumbIds =
{
R.drawable.abc,
R.drawable.def,
R.drawable.klm,
R.drawable.pqr,
R.drawable.rst,
R.drawable.wxy,
R.drawable.xyz,
};
@Override
protected void onCreate(Bundle savedInstanceState)
{
super.onCreate(savedInstanceState);
setContentView(R.layout.showimage);
int position = Integer.parseInt(this.getIntent().getStringExtra("position"));
ImageView jpgView = (ImageView)findViewById(R.id.imageView);
jpgView.setImageResource(mThumbIds[position]);
}
}