Question

Android Studio中的ImageAdapter存在此问题。当我在手机上启动应用程序时，我遇到了巨大的性能问题。所以，人们建议，我应该使用ViewHolder。我查看了其他人如何做到的几十个例子。尝试了许多版本。不过，当我尝试打开该活动时，我的应用程序崩溃了。这是我的代码：

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
}; }

该程序没有任何问题。但是当我打开活动时它会崩溃。当应用程序崩溃时，我使用调试器来查看。

时，应用程序崩溃了

vi.setTag(holder);

应该执行

。我感谢各种帮助。

logcat的：

---------崩溃开始07-21 13：42：19.229 3059-3059 / com.b.a.test E / AndroidRuntime：FATAL 例外：主要过程：com.b.a.test，PID：3059 java.lang.NullPointerException：尝试调用虚方法＆＃39; void android.view.View.setTag（java.lang.Object中）＆＃39;在null对象引用上在 com.b.a.test.ImageAdap.getView（ImageAdap.java:59）在android.widget.AbsListView.obtainView（AbsListView.java:2346）在android.widget.GridView.onMeasure（GridView.java:1065）在android.view.View.measure（View.java:18788）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5951）在android.widget.FrameLayout.onMeasure（FrameLayout.java:194）在 android.support.v7.widget.ContentFrameLayout.onMeasure（ContentFrameLayout.java:135）在android.view.View.measure（View.java:18788）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5951）在 android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1465）在android.widget.LinearLayout.measureVertical（LinearLayout.java:748）在android.widget.LinearLayout.onMeasure（LinearLayout.java:630）在android.view.View.measure（View.java:18788）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5951）在android.widget.FrameLayout.onMeasure（FrameLayout.java:194）在android.view.View.measure（View.java:18788）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5951）在 android.widget.LinearLayout.measureChildBeforeLayout（LinearLayout.java:1465）在android.widget.LinearLayout.measureVertical（LinearLayout.java:748）在android.widget.LinearLayout.onMeasure（LinearLayout.java:630）在android.view.View.measure（View.java:18788）在android.view.ViewGroup.measureChildWithMargins（ViewGroup.java:5951）在android.widget.FrameLayout.onMeasure（FrameLayout.java:194）在 com.android.internal.policy.PhoneWindow $ DecorView.onMeasure（PhoneWindow.java:2643）在android.view.View.measure（View.java:18788）在android.view.ViewRootImpl.performMeasure（ViewRootImpl.java:2100）在android.view.ViewRootImpl.measureHierarchy（ViewRootImpl.java:1216）在android.view.ViewRootImpl.performTraversals（ViewRootImpl.java:1452）在android.view.ViewRootImpl.doTraversal（ViewRootImpl.java:1107）在 android.view.ViewRootImpl $ TraversalRunnable.run（ViewRootImpl.java:6013）在 android.view.Choreographer $ CallbackRecord.run（Choreographer.java:858）在android.view.Choreographer.doCallbacks（Choreographer.java:670）在android.view.Choreographer.doFrame（Choreographer.java:606）在 android.view.Choreographer $ FrameDisplayEventReceiver.run（Choreographer.java:844）在android.os.Handler.handleCallback（Handler.java:739）在android.os.Handler.dispatchMessage（Handler.java:95）在android.os.Looper.loop（Looper.java:148）在android.app.ActivityThread.main（ActivityThread.java:5417） at java.lang.reflect.Method.invoke（Native Method）在 com.android.internal.os.ZygoteInit $ MethodAndArgsCaller.run（ZygoteInit.java:726）在com.android.internal.os.ZygoteInit.main（ZygoteInit.java:616)07-21 13：42：21.620 3059-3059 / com.b.a.test I / Process：发送信号。 PID：3059 SIG：9 07-21 13：42：22.939 3315-3315 / com.b.a.test W / System：引用的ClassLoader 未知路径：/data/app/com.b.a.test-1/lib/x86 07-21 13：42：23.815 3315-3315 / com.b.a.test W / art：之前 Android 4.1，方法android.graphics.PorterDuffColorFilter android.support.graphics.drawable.VectorDrawableCompat.updateTintFilter（android.graphics.PorterDuffColorFilter， android.content.res.ColorStateList，android.graphics.PorterDuff $ Mode）会错误地覆盖package-private方法 android.graphics.drawable.Drawable 07-21 13：42：23.971 3315-3348 / com.b.a.test D / OpenGLRenderer：使用 EGL_SWAP_BEHAVIOR_PRESERVED：true
                                                                       [ 07-21 13:42:24.003  3315: 3315 D/         ]
                                                                       HostConnection::get() New Host Connection established 0xad1b97e0, tid
3315

Answer 1

if(convertView == null)

当断言为真时，您应该扩充布局。因为您的视图为空。像那样;

LayoutInflater inflater = (LayoutInflater)   getContext().getSystemService(Context.LAYOUT_INFLATER_SERVICE); 
view = inflater.inflate(R.layout.mylayout, null);

如果您不想给布局充气，可以这样使用。

View vi = convertView;
ViewHolder holder;

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

Answer 2

您的代码应如下所示

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

您需要先设置视图

Answer 3

View vi = convertView;

if(convertView == null) {
    vi.setTag(holder); 
}

请仔细检查您的代码。简单地说你从null调用setTag，并NullPointerException因此而抛出。

应用不适用于ViewHolder

3 个答案: