calumon calumon - 4 months ago 26
Android Question

App doesn't work with ViewHolder

I have this problem with my ImageAdapter in Android Studio. I have huge performance problems when I start the application on a phone. So, people suggested, I should use a ViewHolder. I looked at dozens of examples on how others did it. tried lot's of versions. Still, my app crashes when I try to open that activity. Here's my code:

public class ImageAdap extends BaseAdapter {
private Context mContext;

public ImageAdap(Context c) {
mContext = c;
}

public int getCount() {
return mThumbIds.length;
}

public Object getItem(int position) {
return null; //mThumbIds[position];
}

public long getItemId(int position) {
return position;
}

static class ViewHolder {
ImageView image;
}

public View getView(int position, View convertView, ViewGroup parent) {

View vi = convertView;
ViewHolder holder;

if(convertView == null) {
holder = new ViewHolder();
holder.image = new ImageView(mContext);
vi.setTag(holder); //Here is the point the app crashes
}
else {
holder = (ViewHolder) vi.getTag();
}

holder.image.setLayoutParams(new GridView.LayoutParams(800, 600));
holder.image.setScaleType(ImageView.ScaleType.CENTER_CROP);
holder.image.setPadding(8, 8, 8, 8);

holder.image.setImageResource(mThumbIds[position]);

return vi;
}

// references to my images
private Integer[] mThumbIds = {
R.drawable.sampleda_01,
R.drawable.sampleda_02,
R.drawable.sampleda_03,
R.drawable.sampleda_04,
R.drawable.sampleda_05
}; }


The program complies without any problem. But it crashes, when I open the activity. So I used debugger to see, when the app crashes. The app crashes, when

vi.setTag(holder);


should be performed. I appreciate every kind of help.

logcat:


--------- beginning of crash 07-21 13:42:19.229 3059-3059/com.b.a.test E/AndroidRuntime: FATAL
EXCEPTION: main
Process: com.b.a.test, PID: 3059
java.lang.NullPointerException: Attempt to invoke virtual method 'void
android.view.View.setTag(java.lang.Object)' on a null object reference
at
com.b.a.test.ImageAdap.getView(ImageAdap.java:59)
at android.widget.AbsListView.obtainView(AbsListView.java:2346)
at android.widget.GridView.onMeasure(GridView.java:1065)
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:135)
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$MethodAndArgsCaller.run(ZygoteInit.java:726)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:616) 07-21
13:42:21.620 3059-3059/com.b.a.test I/Process: Sending
signal. PID: 3059 SIG: 9 07-21 13:42:22.939
3315-3315/com.b.a.test W/System: ClassLoader referenced
unknown path: /data/app/com.b.a.test-1/lib/x86 07-21
13:42:23.815 3315-3315/com.b.a.test W/art: Before
Android 4.1, method android.graphics.PorterDuffColorFilter
android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter(android.graphics.PorterDuffColorFilter,
android.content.res.ColorStateList, android.graphics.PorterDuff$Mode)
would have incorrectly overridden the package-private method in
android.graphics.drawable.Drawable 07-21 13:42:23.971
3315-3348/com.b.a.test D/OpenGLRenderer: Use
EGL_SWAP_BEHAVIOR_PRESERVED: true

[ 07-21 13:42:24.003 3315: 3315 D/ ]
HostConnection::get() New Host Connection established 0xad1b97e0, tid


3315

Answer

your code should look like this

if(convertView == null) {
    holder = new ViewHolder();
    ImageView imageView = new ImageView(mContext);
    vi = imageView;
    holder.image = imageView
    vi.setTag(holder); 
}

You need to set the view first