我的应用程序有一个 Activity ，其中包含许多 TextView ，这些 TextView 用于显示很长的文本 block ，因此我将文本划分为许多 TextView 。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该位置时，就会出现问题。但是当我更改屏幕方向时，应用程序崩溃了。
下面是代码:
第1章.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>
第1章.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);
}
});
}
}
日志猫:
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)
谢谢大家修复了 ClassCastException，但现在当方向改变时似乎没有保存和保留滚动位置。
最佳答案
您遇到了强制转换异常，这很明显，因为您正在将RelativeLayout强制转换为 TextView 行
final TextView textView = (TextView)scrollView.getChildAt(0);
ScrollView 在 0 处的直接子级是relativelayout，如布局中所示。
关于java - 当我尝试保存滚动位置时应用程序崩溃，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/24822860/