Question

我的应用程序有一个活动，其中包含许多文本视图，用于显示非常长的文本块，因此我将文本分成许多文本视图。当我尝试保存文本的滚动位置以进行方向更改并在应用程序进入后台时保留位置时，会出现问题。但是当我改变屏幕的方向时，应用程序崩溃了。

以下是代码：

Chapter1.xml

<?xml version="1.0" encoding="utf-8"?>

<ScrollView xmlns:android="http://schemas.android.com/apk/res/android"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:id="@+id/scrollChapter1">
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
                android:layout_width="match_parent"
                android:layout_height="match_parent">
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:text="@string/Chapter1"
            android:textSize="17sp"
            android:padding="10px"
            android:id="@+id/txtChapter1Title"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="15dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentA"
            android:id="@+id/txtChapter1A"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1Title"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentB"
            android:id="@+id/txtChapter1B"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1A"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentC"
            android:id="@+id/txtChapter1C"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1B"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentD"
            android:id="@+id/txtChapter1D"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1C"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentE"
            android:id="@+id/txtChapter1E"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1D"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentF"
            android:id="@+id/txtChapter1F"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1E"
            />
    <TextView
            android:layout_width="fill_parent"
            android:layout_height="wrap_content"
            android:layout_marginTop="0dip"
            android:width="0dip"
            android:textSize="16sp"
            android:padding="10px"
            android:text="@string/Chapter1ContentG"
            android:id="@+id/txtChapter1G"
            android:maxLength="9000"
            android:layout_below="@+id/txtChapter1F"
            />
</RelativeLayout>
</ScrollView>

Chapter1.java：

public class chapter1 extends Activity {
@Override
public void onCreate(Bundle savedInstanceState){
    super.onCreate(savedInstanceState);
    setContentView(R.layout.chapter1);
    WindowManager w = getWindowManager();
    Display d = w.getDefaultDisplay();
    if(d.getWidth() > d.getHeight()){
        Log.d("Orientation", "Landscape");
    }else{
        Log.d("Orientation", "Potrait");
    }
}
@Override
protected void onSaveInstanceState(Bundle outState){
    super.onSaveInstanceState(outState);
    final ScrollView scrollView = (ScrollView) findViewById(R.id.scrollChapter1);
    final TextView textView = (TextView) scrollView.getChildAt(0); //Crashes at this line
    final int firstVisibleLineOffset = textView.getLayout().getLineForVertical(scrollView.getScrollY());
    final int firstVisibleCharacterOffset = textView.getLayout().getLineStart(firstVisibleLineOffset);
    outState.putInt("ScrollViewContainerTextViewFirstVisibleCharacterOffset", firstVisibleCharacterOffset);
}
@Override
protected void onRestoreInstanceState(Bundle savedInstanceState){
    super.onRestoreInstanceState(savedInstanceState);
    final int firstVisibleCharacterOffset = savedInstanceState.getInt("ScrollViewContainerTextViewFirstVisibleCharacterOffset");
    final ScrollView scrollView = (ScrollView) findViewById(R.id.scrollChapter1);
    scrollView.post(new Runnable() {
        @Override
        public void run() {
            final TextView textView = (TextView) scrollView.getChildAt(0);
            final int firstVisibleLineOffset = textView.getLayout().getLineStart(firstVisibleCharacterOffset);
            final int pixelOffset = textView.getLayout().getLineTop(firstVisibleLineOffset);
            scrollView.scrollTo(0, pixelOffset);
        }
    });
}

}

logcat的：

07-18 15:52:39.921      806-806/com.example.ZindaRud D/Orientation﹕ Potrait
07-18 15:52:41.800      806-810/com.example.ZindaRud D/dalvikvm﹕ GC_CONCURRENT freed 155K, 4% free 7169K/7431K, paused 6ms+6ms
07-18 15:52:41.809      806-806/com.example.ZindaRud D/Orientation﹕ Potrait
07-18 15:52:44.500      806-806/com.example.ZindaRud W/TextLayoutCache﹕ computeValuesWithHarfbuzz -- need to force to single run
07-18 15:52:48.760      806-806/com.example.ZindaRud D/AndroidRuntime﹕ Shutting down VM
07-18 15:52:48.760      806-806/com.example.ZindaRud W/dalvikvm﹕ threadid=1: thread exiting with uncaught exception (group=0x409961f8)
07-18 15:52:48.809      806-806/com.example.ZindaRud E/AndroidRuntime﹕ FATAL EXCEPTION: main
java.lang.ClassCastException: android.widget.RelativeLayout cannot be cast to android.widget.TextView
        at com.example.ZindaRud.chapter1.onSaveInstanceState(chapter1.java:31)
        at android.app.Activity.performSaveInstanceState(Activity.java:1113)
        at android.app.Instrumentation.callActivityOnSaveInstanceState(Instrumentation.java:1185)
        at android.app.ActivityThread.handleRelaunchActivity(ActivityThread.java:3321)
        at android.app.ActivityThread.access$700(ActivityThread.java:122)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1150)
        at android.os.Handler.dispatchMessage(Handler.java:99)
        at android.os.Looper.loop(Looper.java:137)
        at android.app.ActivityThread.main(ActivityThread.java:4340)
        at java.lang.reflect.Method.invokeNative(Native Method)
        at java.lang.reflect.Method.invoke(Method.java:511)
        at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551)
        at dalvik.system.NativeStart.main(Native Method)

谢谢你们修复了ClassCastException，但是现在它似乎没有保存并在方向改变时保留滚动位置。

Answer 1

您正在获得强制转换异常，因为您将RelativeLayout强制转换为

行的TextView

final TextView textView = (TextView) scrollView.getChildAt(0);

ScrollView在0的直接子节点是RelativeLayout，如布局中所示。

Answer 2

你必须像对此错误一样使用它。重用@ micro.pavo所说的

final RelativeLayout rLayout = (RelativeLayout) scrollView.getChildAt(0);
final TextView textView = (TextView) rLayout.getChildAt(0);

或者您可以直接访问

final TextView textView = (TextView)findViewById(R.id.txtChapter1Title);

Answer 3

final TextView textView =（TextView）scrollView.getChildAt（0）; //在此行崩溃

RelativeLayout是ScrollView的孩子，您将其投放到TextView。

所以，

java.lang.ClassCastException：android.widget.RelativeLayout不能强制转换为android.widget.TextView

Answer 4

您收到ClassCastException，因为您试图在此行中RelativeLayout投放TextView

final TextView textView = (TextView) scrollView.getChildAt(0);

如xml代码所示，ScrollView下的第一个孩子是RelativeLayout，请尝试将其设为：

final RelativeLayout rLayout = (RelativeLayout) scrollView.getChildAt(0);

当我尝试保存滚动位置时，应用程序崩溃

4 个答案: