Android:如何使用View的setTag,getTag和findViewWithTag方法？

Question

我的Android应用程序的一段代码遇到了一些麻烦.我NullPointerException在尝试设置ImageView对象的背景时不断得到.

这是代码:

public View getView(int position, View view, ViewGroup parent) {
    ImageView imageView;
    if (view == null) {
        imageView = new ImageView(mContext);
    } else {
        imageView = (ImageView) view;
    }
    imageView.setTag(position);
    return imageView;
}

private OnItemClickListener itemClickListener = new OnItemClickListener() {
    @Override
    public void onItemClick(AdapterView<?> parent, View v, int position, long id) {

        ImageView imageView;
        //Variable i, here, is from a for loop.
        imageView = (ImageView)v.findViewWithTag(i);
        //I get a NullPointerException at the next line, "Log.d"
        Log.d("View 1", imageView.toString());
        //If I get rid of the "Log.d" line above, 
        //the NullPointerException occurs on the next line
        imageView.setBackgroundColor(Color.BLUE);
        imageView = (ImageView)v.findViewWithTag(position);

        Log.d("View 2", imageView.toString());
        imageView.setBackgroundColor(Color.BLUE);

    };
}

我怀疑我的代码问题是因为我传递的setTag()方法是什么参数以及我传递方法的参数是什么findViewWithTag().如果有人可以向我展示如何设置标签和使用标签查找视图的示例,我将非常感激.

感谢您的时间.

编辑:这是错误日志.我不知道该把它放在哪里,所以我会把它放在这里.

05-04 21:47:24.314: ERROR/AndroidRuntime(335): FATAL EXCEPTION: main
05-04 21:47:24.314: ERROR/AndroidRuntime(335): java.lang.NullPointerException
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at com.jacksmartie.PhotoMem.MainActivity$1.onItemClick(MainActivity.java:79)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at android.widget.AdapterView.performItemClick(AdapterView.java:284)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at android.widget.AbsListView$PerformClick.run(AbsListView.java:1696)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at android.os.Handler.handleCallback(Handler.java:587)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at android.os.Handler.dispatchMessage(Handler.java:92)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at android.os.Looper.loop(Looper.java:123)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at android.app.ActivityThread.main(ActivityThread.java:4627)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at java.lang.reflect.Method.invokeNative(Native Method)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at java.lang.reflect.Method.invoke(Method.java:521)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:868)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:626)
05-04 21:47:24.314: ERROR/AndroidRuntime(335):     at dalvik.system.NativeStart.main(Native Method)`

Answer 1

这条线是你罪魁祸首的一部分:

com.jacksmartie.PhotoMem.MainActivity$1.onItemClick(MainActivity.java:79)

在这里放一个断点:

Log.d("View 1", imageView.toString());

看看你的imageview参考对象[imageView]是什么,我期待它是null,因为你没有正确链接它.

如果为null,则表示您指向参考视图的链接不正确.如果是这种情况,那么你需要正确分配它,如下所示:

Button b = findViewById(R.id.Button01);

然而; 因为你正在使用看起来似乎是a的东西ListView,所以它的拉动略有不同.这意味着你拉动视图的方式是错误的,做一些研究,应该找到一些东西来帮助清除它!