Question

恢复活动时，我需要帮助保存我的scrollview的位置。我有一个包含一些按钮的长滚动视图。当我点击这些按钮时，会打开新的活动。当我恢复scrollview的活动时，scrollview从顶部开始，用户必须再次滚动。这很烦人。

如何保存滚动视图位置？

我发现了这一点，但是行Util.Log("X:" + scrollX + " Y:" + scrollY);不起作用：

//  two static variable,
public static int scrollX = 0;
public static int scrollY = -1;

//update & save their value on onPause & onResume.
@Override
protected void onPause()
{
  super.onPause();
  scrollX = scrollView.getScrollX();
  scrollY = scrollView.getScrollY();
}
@Override
protected void onResume()
{
  Util.Log("X:" + scrollX + " Y:" + scrollY);
  super.onResume();
  //this is important. scrollTo doesn't work in main thread.
  scrollView.post(new Runnable()
{
@Override
public void run()
{
  scrollView.scrollTo(scrollX, scrollY);
}
});
}

感谢您的帮助！：d

编辑：

如果我删除该行，我会收到此错误：

 01-01 17:29:11.023: E/AndroidRuntime(1967): FATAL EXCEPTION: main
01-01 17:29:11.023: E/AndroidRuntime(1967): Process: com.example.appquiz, PID: 1967
01-01 17:29:11.023: E/AndroidRuntime(1967): java.lang.RuntimeException: Unable to resume activity {com.example.appquiz/com.example.appquiz.Categories}: java.lang.NullPointerException
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2808)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:2837)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2270)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.access$800(ActivityThread.java:145)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1206)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.os.Handler.dispatchMessage(Handler.java:102)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.os.Looper.loop(Looper.java:136)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.main(ActivityThread.java:5081)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at java.lang.reflect.Method.invokeNative(Native Method)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at java.lang.reflect.Method.invoke(Method.java:515)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:781)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at dalvik.system.NativeStart.main(Native Method)
01-01 17:29:11.023: E/AndroidRuntime(1967): Caused by: java.lang.NullPointerException
01-01 17:29:11.023: E/AndroidRuntime(1967):     at com.example.appquiz.Categories.onResume(Categories.java:82)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1192)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.Activity.performResume(Activity.java:5319)
01-01 17:29:11.023: E/AndroidRuntime(1967):     at android.app.ActivityThread.performResumeActivity(ActivityThread.java:2798)
01-01 17:29:11.023: E/AndroidRuntime(1967):     ... 12 more

我的整个代码：

public static int scrollX = 0;
public static int scrollY = -1;
ScrollView scrollView = (ScrollView) findViewById(R.id.Scrollview);

//blabla

onCreate //...

@Override
protected void onPause() {
// TODO Auto-generated method stub
    scrollX = scrollView.getScrollX();
    scrollY = scrollView.getScrollY();
    super.onPause();
    }

@Override
protected void onResume() {
// TODO Auto-generated method stub
    super.onResume();
    scrollView.post(new Runnable(){
     @Override
     public void run(){
       scrollView.scrollTo(scrollX, scrollY);}});}

Answer 1

将此代码添加到inflateView方法的末尾，请确保R.id.Scrollview是正确的ID

scrollView = (ScrollView) findViewById(R.id.Scrollview);

顺便说一下，你不应该使用post方法来做到这一点。滚动视图的最佳方法是执行以下操作：

ViewTreeObserver vto = scrollView.getViewTreeObserver();
vto.addOnGlobalLayoutListener(new OnGlobalLayoutListener() {
    public void onGlobalLayout() {
        scrollView.scrollTo(0, 0);
    }
});

如果这没有用，请告诉我们这是什么行：（com.example.appquiz.Categories.onResume（Categories.java:82））

Answer 2

Util.Log（“X：”+ scrollX +“Y：”+ scrollY）;删除此代码dude这只是记录代码而与功能无关

如何保存和恢复ScrollPosition

2 个答案: