我有一个Actionbar和一些片段.问题是我的主屏幕.有一个概述左侧的片段和右侧的细节片段.我的TabListener是动态的,所以我想以编程方式设置我的布局的重量.每当我尝试获取我的LinearLayout的Layoutparams我得到一个ClassCastException：

12-22 16:00:37.620: W/System.err(7235): java.lang.classCastException: android.widget.FrameLayout$LayoutParams cannot be cast to android.widget.LinearLayout$LayoutParams
12-22 16:00:37.625: W/System.err(7235):     at com.coover.eu.lostandfound.ListSearchFragment.onViewCreated(ListSearchFragment.java:184)
12-22 16:00:37.625: W/System.err(7235):     at android.support.v4.app.FragmentManagerImpl.movetoState(FragmentManager.java:884)
12-22 16:00:37.630: W/System.err(7235):     at android.support.v4.app.FragmentManagerImpl.movetoState(FragmentManager.java:1080)
12-22 16:00:37.630: W/System.err(7235):     at android.support.v4.app.BackStackRecord.run(BackStackRecord.java:622)
12-22 16:00:37.630: W/System.err(7235):     at android.support.v4.app.FragmentManagerImpl.execPendingActions(FragmentManager.java:1416)
12-22 16:00:37.630: W/System.err(7235):     at android.support.v4.app.FragmentActivity.onStart(FragmentActivity.java:505)
12-22 16:00:37.630: W/System.err(7235):     at android.app.Instrumentation.callActivityOnStart(Instrumentation.java:1178)
12-22 16:00:37.635: W/System.err(7235):     at android.app.Activity.performStart(Activity.java:5216)
12-22 16:00:37.635: W/System.err(7235):     at android.app.ActivityThread.performlaunchActivity(ActivityThread.java:2083)
12-22 16:00:37.635: W/System.err(7235):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
12-22 16:00:37.635: W/System.err(7235):     at android.app.ActivityThread.access$700(ActivityThread.java:140)
12-22 16:00:37.635: W/System.err(7235):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1237)
12-22 16:00:37.640: W/System.err(7235):     at android.os.Handler.dispatchMessage(Handler.java:99)
12-22 16:00:37.640: W/System.err(7235):     at android.os.Looper.loop(Looper.java:137)
12-22 16:00:37.640: W/System.err(7235):     at android.app.ActivityThread.main(ActivityThread.java:4921)
12-22 16:00:37.640: W/System.err(7235):     at java.lang.reflect.Method.invokeNative(Native Method)
12-22 16:00:37.640: W/System.err(7235):     at java.lang.reflect.Method.invoke(Method.java:511)
12-22 16:00:37.645: W/System.err(7235):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:1038)
12-22 16:00:37.645: W/System.err(7235):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:805)
12-22 16:00:37.645: W/System.err(7235):     at dalvik.system.NativeStart.main(Native Method)

膨胀的布局：

<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical" 
    android:id="@+id/container_found_list_overview">

    <EditText android:id="@+id/search_Box" 
        android:layout_width="fill_parent"
        android:layout_height="50dp"
        android:padding="5dp"
        android:textSize="35sp"
        android:hint="@string/search"
        android:inputType="text"
        android:maxLines="1"/>
    <ListView 
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/overview_list_view">
    </ListView>

</LinearLayout>

代码：

LinearLayout myView = (LinearLayout)this.getView().findViewById(R.id.container_found_list_overview);
            Log.d("found container",""+(myView != null));
            try{
                LayoutParams lp = (LayoutParams) myView.getLayoutParams();
                lp.weight = 1;
                lp.width = 0;
                myView.setLayoutParams(lp);
            }
            catch(RuntimeException e){
                Log.e("cant get layoutparams",e.getMessage());
                e.printstacktrace();
            }

发生的是一个视图的LayoutParams实际上是父类的类型.在这种情况下,您将获得一个FrameLayout $LayoutParams,因为您的LinearLayout位于FrameLayout中.

为什么是父母的类型？这是因为他们存储对父母有用的信息.如果要检索EditText或ListView的布局参数,您将获得LinearLayout $LayoutParams.

我正在尝试开发 Android 3.1平板电脑应用程序.

这个应用程序将有很多图像,我已经按照Processing Bitmaps Off the UI Thread教程,但我做错了,因为我得到：

java.lang.classCastException：android.widget.AbsListView $LayoutParams无法强制转换为android.widget.gallery $LayoutParams

这是我的代码：

我在一个Activity上设置了gallery

mFactgallery = (gallery)mView.findViewById(R.id.factgallery);
mFactgallery.setAdapter(new ImagegalleryAdapter(mActivity,ImageView.ScaleType.FIT_END,180,90));

ImagegalleryAdapter.java

public class ImagegalleryAdapter extends BaseAdapter
{
    private ArrayList<String> mImagesPath;
    private Context mContext;
    private int mWidth;
    private int mHeight;

    public ArrayList<String> getmImagesPath()
    {
        return mImagesPath;
    }

    public void setmImagesPath(ArrayList<String> mImagesPath)
    {
        this.mImagesPath = mImagesPath;
    }

    public void addImage(String imagePath)
    {
        mImagesPath.add(imagePath);
    }

    public ImagegalleryAdapter(Context context,ImageView.ScaleType scaleType,int width,int height)
    {
        mContext = context;
        mWidth = width;
        mHeight = height;
        mScaleType = scaleType;

        mImagesPath = new ArrayList<String>();
    }

    @Override
    public int getCount()
    {
        return mImagesPath.size();
    }

    @Override
    public Object getItem(int position)
    {
        return position;
    }

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

    @Override
    public View getView(int position,View convertView,ViewGroup parent)
    {
        // Get a View to display image data                     
        ImageView imageView;
        // if it's not recycled,initialize some attributes
        if (convertView == null)
        {
            imageView = new ImageView(mContext);
            imageView.setScaleType(ImageView.ScaleType.CENTER_CROP);
            imageView.setLayoutParams(new GridView.LayoutParams(
                    LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT));
        }
        else
        {
            imageView = (ImageView) convertView;
            // Recicla el Bitmap.
            Bitmap bm = ((BitmapDrawable) imageView.getDrawable()).getBitmap();
            if (bm != null)
                bm.recycle();
        }

        String filePath = mImagesPath.get(position);
        if (BitmapTools.cancelPotentialWork(filePath,imageView))
        {
            String[] params = {filePath,Integer.toString(mWidth),Integer.toString(mHeight)};
            final BitmapWorkerTask task = new BitmapWorkerTask(imageView);
            final AsyncDrawable asyncDrawable =
                    new AsyncDrawable(mContext.getResources(),filePath,task);
            imageView.setimageDrawable(asyncDrawable);
            task.execute(params);
        }

        return imageView;
    }
}

BitmapWorkerTask.java

public class BitmapWorkerTask extends AsyncTask<String,Void,Bitmap>
{
    private final WeakReference<ImageView> imageViewReference;
    public String imgPath = "";

    public BitmapWorkerTask(ImageView imageView) {
        // Use a WeakReference to ensure the ImageView can be garbage collected
        imageViewReference = new WeakReference<ImageView>(imageView);
    }

    // Decode image in background.
    @Override
    protected Bitmap doInBackground(String... params)
    {
        imgPath = params[0];
        int width = Integer.valueOf(params[1]).intValue();
        int height = Integer.valueOf(params[2]).intValue();
        return BitmapTools.decodeSampledBitmapFromdisk(imgPath,width,height);
    }

    // Once complete,see if ImageView is still around and set bitmap.
    @Override
    protected void onPostExecute(Bitmap bitmap)
    {
        if (isCancelled())
        {
            bitmap = null;
        }

        if (imageViewReference != null && bitmap != null)
        {
            final ImageView imageView = imageViewReference.get();
            final BitmapWorkerTask bitmapWorkerTask =
                    BitmapTools.getBitmapWorkerTask(imageView);
            if (this == bitmapWorkerTask && imageView != null)
            {
                imageView.setimageBitmap(bitmap);
            }
        }
    }
}

AsyncDrawable.java

public class AsyncDrawable extends BitmapDrawable
{
    private final WeakReference<BitmapWorkerTask> bitmapWorkerTaskReference;

    public AsyncDrawable(Resources res,String filepath,BitmapWorkerTask bitmapWorkerTask)
    {
        super(res,filepath);
        bitmapWorkerTaskReference =
            new WeakReference<BitmapWorkerTask>(bitmapWorkerTask);
    }

    public BitmapWorkerTask getBitmapWorkerTask()
    {
        return bitmapWorkerTaskReference.get();
    }
}

我究竟做错了什么？

用gallery.LayoutParams替换GridView.LayoutParams,如下所示,这将解决您的问题

imageView.setLayoutParams(new gallery.LayoutParams(
                    LayoutParams.MATCH_PARENT,LayoutParams.MATCH_PARENT));

我试图实现ViewHolder模式,以便在绘图上绘制地图时提高性能.
我需要为我的标记创建一些标签.在draw()中的数据处理中调用此方法

// Now we create label view and convert it into bitmap
private Bitmap createLabelBitmap(GisLaborHistoryObject object,HistoryPoint point) {
    // create view from xml
    if (vh == null) {
        vh = new ViewHolder();
        vh.view = inflater.inflate(R.layout.map_gis_history_label,null,false);
        vh.tv = (TextView) vh.view.findViewById(R.id.gislabeltext);
    }

    // set label content
    if (vh.tv != null) {
        if (!mSingleLaborHistory) {
            String name = "";
            name = object.getdisplayName();
            if (name == null || "".equals(name))
                name = object.getPersonId();
            if (name == null || "".equals(name))
                name = object.getLaborCode();
            if (name == null)
                name = "";

            vh.tv.setText(name);
        } else
            vh.tv.setText(point.getChangeDate());
    } 
    // measure resulting view
    vh.view.measure(spec,spec);
    vh.view.layout(0,vh.view.getMeasuredWidth(),vh.view.getMeasuredHeight());
    Bitmap b = Bitmap.createBitmap(vh.view.getWidth(),vh.view.getHeight(),Bitmap.Config.ARGB_8888);
    canvasToDraw.setBitmap(b);
    canvasToDraw.translate(-vh.view.getScrollX(),-vh.view.getScrollY());
    vh.view.draw(canvasToDraw);
    return b;
}

规格是

spec = MeasureSpec.makeMeasureSpec(0,MeasureSpec.UNSPECIFIED);

结果是
logcat的：

04-29 17:12:34.057: E/AndroidRuntime(389): java.lang.NullPointerException
 04-29 17:12:34.057: E/AndroidRuntime(389):     at android.widget.TextView.checkForRelayout(TextView.java:5497)
 04-29 17:12:34.057: E/AndroidRuntime(389):     at android.widget.TextView.setText(TextView.java:2730)
 04-29 17:12:34.057: E/AndroidRuntime(389):     at android.widget.TextView.setText(TextView.java:2598)
 04-29 17:12:34.057: E/AndroidRuntime(389):     at android.widget.TextView.setText(TextView.java:2573)
 04-29 17:12:34.057: E/AndroidRuntime(389):     at com.xxx.android.proj.ui.map.overlays.LaborsMarkerOverlay.createLabelBitmap(LaborsMarkerOverlay.java:164)

我使用的XML布局

<?xml version="1.0" encoding="utf-8"?>
<TextView xmlns:android="http://schemas.android.com/apk/res/android"
android:id="@+id/gislabeltext"android:layout_width="wrap_content"
android:layout_height="wrap_content"
android:paddingLeft="2dp"
android:paddingRight="2dp" />

可能是这个错误的原因？

在看到android source code在5497行我注意到有一个检查使用mLayoutParams.我在调试模式下看起来就是这样,真的是空的！
我添加明确设置此参数的行.现在一切正常

vh.tv = (TextView) vh.view.findViewById(R.id.gislabeltext);
vh.tv.setLayoutParams(new ViewGroup.LayoutParams(LayoutParams.WRAP_CONTENT,LayoutParams.WRAP_CONTENT));

我的错误是,当使用ViewGroup膨胀时,我必须显式设置LayoutParams root = null;一切正常,直到我尝试重用TextView乘法时间.