这是我的主要活动类文件：
public class product extends AppCompatActivity {
String name[] = {
"q",
"w",
"e",
"r",
"t",
"y",
"u"
};
Integer pisc[] = {
R.drawable.a,
R.drawable.e,
R.drawable.c,
R.drawable.d,
R.drawable.e,
R.drawable.a,
R.drawable.d
};
String location[] = {
"a",
"s",
"dr",
"d",
"f",
"r",
"r"
};
String lang[] = {
"Hindi",
"Hindi",
"Hindi",
"Hindi",
"Hindi",
"Hindi",
"Hindi"
};
Float rating[] = {
5f,
4.5f,
4.5f,
4f,
4f,
3.5f,
3f
};
String rate[] = {
"Rated by 452+ people",
"Rated by 427+ people",
"Rated by 369+ people",
"Rated by 332+ people",
"Rated by 279+ people",
"Rated by 259+ people",
"Rated by 129+ people"
};
TextView naam,loc,langs,rat;
Button thumbnails;
ListView hind;
RatingBar rates;
@Override
protected void onCreate(Bundle savedInstanceState) {
super.onCreate(savedInstanceState);
setContentView(R.layout.activity_product);
hind = (ListView) findViewById(R.id.hindpro);
naam = (TextView) findViewById(R.id.nameh);
loc = (TextView) findViewById(R.id.locations);
langs = (TextView) findViewById(R.id.lang);
rat = (TextView) findViewById(R.id.rating);
thumbnails = (Button) findViewById(R.id.pic);
rates = (RatingBar)findViewById(R.id.ratingBar);
class customadapterpz extends BaseAdapter {
@Override
public int getCount() {
return name.length;
}
@Override
public Object getItem(int position) {
return null;
}
@Override
public long getItemId(int position) {
return 0;
}
@Override
public View getView(int positionq, View convertView, ViewGroup
parent) {
View view4 = getLayoutInflater().inflate(R.layout.hindpro,
null);
if (name[positionq] != null) {
Bitmap bitmahind =
decodeSampledBitmapFromResource(product.this.getResources(),
pisc[positionq], 150, 150);
BitmapDrawable bitmapDrawableaw = new
BitmapDrawable(getResources(), bitmahind);
thumbnails.setBackgroundDrawable(bitmapDrawableaw);
// thumbnails.setImageBitmap(bitmahind);
naam.setText(name[positionq]);
loc.setText(location[positionq]);
langs.setText(lang[positionq]);
rat.setText(rate[positionq]);
rates.setRating(rating[positionq]);
}
return view4;
}
}
customadapterpz item23 = new customadapterpz();
hind.setAdapter(item23);
}
public static Bitmap decodeSampledBitmapFromResource(Resources res, int
resId, int reqWidth, int reqHeight) {
// First decode with inJustDecodeBounds=true to check dimensions
final BitmapFactory.Options options = new BitmapFactory.Options();
options.inJustDecodeBounds = true;
BitmapFactory.decodeResource(res, resId, options);
// Calculate inSampleSize
options.inSampleSize = calculateInSampleSize(options, reqWidth,
reqHeight);
// Decode bitmap with inSampleSize set
options.inJustDecodeBounds = false;
return BitmapFactory.decodeResource(res, resId, options);
}
public static int calculateInSampleSize(BitmapFactory.Options options,
int reqWidth, int reqHeight) {
// Raw height and width of image
final int height = options.outHeight;
final int width = options.outWidth;
int inSampleSize = 4;
if (height > reqHeight || width > reqWidth) {
final int halfHeight = height / 8;
final int halfWidth = width / 8;
// Calculate the largest inSampleSize value that is a power of 2
and keeps both
// height and width larger than the requested height and width.
while ((halfHeight / inSampleSize) >= reqHeight
&& (halfWidth / inSampleSize) >= reqWidth) {
inSampleSize *= 8;
}
}
return inSampleSize;
}
}
这个xml的活动：
<RelativeLayout>
<TextView
android:id="@+id/sometextview"
android:layout_width="match_parent"
android:layout_height="60dp"
android:text="Some Text"
android:textColor="#FFFFFF"
android:background="#000000"
android:textSize="25sp"
android:gravity="center"
android:layout_alignParentTop="true"
android:layout_centerHorizontal="true"
/>
<ListView
android:layout_width="match_parent"
android:layout_height="wrap_content"
android:id="@+id/hindpro"
android:layout_below="@+id/textView2">
</ListView>
</RelativeLayout>
listview的自定义xml文件：
<RelativeLayout>
<Button
android:id="@+id/pic"
android:layout_width="120dp"
android:layout_height="150dp"
android:layout_marginStart="11dp"
android:layout_marginTop="13dp"
android:layout_marginBottom="11dp"
android:layout_alignParentTop="true"
android:layout_alignParentStart="true" />
<TextView
android:id="@+id/nameh"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignParentStart="true"
android:layout_alignParentTop="true"
android:layout_marginStart="149dp"
android:textColor="#FFFFFF"
android:layout_marginTop="14dp"
android:textSize="20sp"
android:text="Name" />
<TextView
android:id="@+id/locations"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:layout_alignStart="@+id/nameh"
android:layout_below="@+id/nameh"
android:text="Mansarovar, jaipur" />
<TextView
android:id="@+id/lang"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:textSize="12sp"
android:text="Hindi"
android:layout_below="@+id/locations"
android:layout_alignStart="@+id/locations" />
<RatingBar
android:id="@+id/ratingBar"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
style="?android:attr/ratingBarStyleSmall"
android:scaleX="2"
android:scaleY="2"
android:layout_centerVertical="true"
android:layout_alignEnd="@+id/locations" />
<TextView
android:id="@+id/rating"
android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:text="Rated by 129 people"
android:textSize="10sp"
android:layout_above="@+id/book"
android:layout_alignStart="@+id/lang" />
<Button
android:id="@+id/book"
android:layout_width="wrap_content"
android:layout_marginRight="10dp"
android:layout_height="wrap_content"
android:text="BOOK"
android:layout_alignBottom="@+id/pic"
android:layout_alignParentEnd="true" />
</RelativeLayout>
当我尝试从另一个活动打开此活动时，我收到空指针异常
我尝试了所有我知道的事情，包括仔细检查每一行代码并重命名每个标记，以便它们与任何其他标记不匹配。 所以请大家，看看代码并告诉我出了什么问题。
logcat的：
05-27 21:56:19.974 22216-22216/com.example.pankaz.qw E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.pankaz.qw, PID: 22216
java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.Button.setBackgroundDrawable(android.graphics.drawable.Drawable)' on a null object reference
at com.example.pankaz.qw.product$1customadapterpz.getView(product.java:137)
at android.widget.AbsListView.obtainView(AbsListView.java:2346)
at android.widget.ListView.measureHeightOfChildren(ListView.java:1280)
at android.widget.ListView.onMeasure(ListView.java:1188)
at android.view.View.measure(View.java:18788)
at android.widget.RelativeLayout.measureChild(RelativeLayout.java:676)
at android.widget.RelativeLayout.onMeasure(RelativeLayout.java:479)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.support.v7.widget.ContentFrameLayout.onMeasure(ContentFrameLayout.java:139)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.LinearLayout.measureChildBeforeLayout(LinearLayout.java:1465)
at android.widget.LinearLayout.measureVertical(LinearLayout.java:748)
at android.widget.LinearLayout.onMeasure(LinearLayout.java:630)
at android.view.View.measure(View.java:18788)
at android.view.ViewGroup.measureChildWithMargins(ViewGroup.java:5951)
at android.widget.FrameLayout.onMeasure(FrameLayout.java:194)
at com.android.internal.policy.PhoneWindow$DecorView.onMeasure(PhoneWindow.java:2643)
at android.view.View.measure(View.java:18788)
at android.view.ViewRootImpl.performMeasure(ViewRootImpl.java:2100)
at android.view.ViewRootImpl.measureHierarchy(ViewRootImpl.java:1216)
at android.view.ViewRootImpl.performTraversals(ViewRootImpl.java:1452)
at android.view.ViewRootImpl.doTraversal(ViewRootImpl.java:1107)
at android.view.ViewRootImpl$TraversalRunnable.run(ViewRootImpl.java:6013)
at android.view.Choreographer$CallbackRecord.run(Choreographer.java:858)
at android.view.Choreographer.doCallbacks(Choreographer.java:670)
at android.view.Choreographer.doFrame(Choreographer.java:606)
at android.view.Choreographer$FrameDisplayEventReceiver.run(Choreographer.java:844)
at android.os.Handler.handleCallback(Handler.java:739)
at android.os.Handler.dispatchMessage(Handler.java:95)
at android.os.Looper.loop(Looper.java:148)
at android.app.ActivityThread.main(ActivityThread.java:5417)
at java.lang.reflect.Method.invoke(Native Method)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616)
答案 0 :(得分：0)
这是因为你在onCreate（）中初始化了缩略图。您应该在适配器内初始化它。将 LayoutInflater 传递给适配器。然后使用适配器内的LayoutInflater初始化缩略图。