Question

我试图找出WebView滚动是否已经结束。我试图通过使用下面的代码找到它。我得到了ClassCastException。请帮帮我：

这是界面：

public interface ScrollViewListener {
void onScrollChanged(ScrollViewExt scrollView, 
        int x, int y, int oldx, int oldy);
}

这是扩展ScrollView：

的类

public class ScrollViewExt extends ScrollView {
private ScrollViewListener scrollViewListener = null;
public ScrollViewExt(Context context) {
    super(context);
}

public ScrollViewExt(Context context, AttributeSet attrs, int defStyle) {
    super(context, attrs, defStyle);
}

public ScrollViewExt(Context context, AttributeSet attrs) {
    super(context, attrs);
}

public void setScrollViewListener(ScrollViewListener scrollViewListener) {
    this.scrollViewListener = scrollViewListener;
}

@Override
protected void onScrollChanged(int l, int t, int oldl, int oldt) {
    super.onScrollChanged(l, t, oldl, oldt);
    if (scrollViewListener != null) {
        scrollViewListener.onScrollChanged(this, l, t, oldl, oldt);
    }
}
}

这是我的活动课程：

public class MainActivity extends Activity implements ScrollViewListener{

ScrollViewExt sv;
WebView wv;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    sv = (ScrollViewExt) findViewById(R.id.scrollTest);
    sv.setScrollViewListener(this);

    wv = (WebView) findViewById(R.id.webTest);
    wv.loadUrl("some url");
}

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.main, menu);
    return true;
}

@Override
public void onScrollChanged(ScrollViewExt scrollView, int x, int y,
        int oldx, int oldy) {
    // TODO Auto-generated method stub
     View view = (View) scrollView.getChildAt(scrollView.getChildCount() - 1);
        int diff = (view.getBottom() - (scrollView.getHeight() + scrollView.getScrollY()));

        // if diff is zero, then the bottom has been reached
        if (diff == 0) {
            // do stuff
            System.out.println("in here---->>>");
        }

}

}

这是我的布局xml：

<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
xmlns:tools="http://schemas.android.com/tools"
android:layout_width="match_parent"
android:layout_height="match_parent"
android:paddingBottom="@dimen/activity_vertical_margin"
android:paddingLeft="@dimen/activity_horizontal_margin"
android:paddingRight="@dimen/activity_horizontal_margin"
android:paddingTop="@dimen/activity_vertical_margin"
tools:context=".MainActivity" >

    <ScrollView 
        android:id="@+id/scrollTest"
        android:layout_height="600dp"
        android:layout_width="match_parent">
            <WebView 
                android:id="@+id/webTest"
                android:layout_height="600dp"
                android:layout_width="match_parent"/>
    </ScrollView>


</RelativeLayout>

这是我的例外：

03-11 10:55:58.744: E/AndroidRuntime(27404): FATAL EXCEPTION: main
03-11 10:55:58.744: E/AndroidRuntime(27404): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.scrolltest/com.example.scrolltest.MainActivity}: java.lang.ClassCastException: android.widget.ScrollView cannot be cast to com.demo.listener.ScrollViewExt
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2084)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.access$600(ActivityThread.java:130)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1195)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.os.Handler.dispatchMessage(Handler.java:99)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.os.Looper.loop(Looper.java:137)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.main(ActivityThread.java:4745)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at java.lang.reflect.Method.invokeNative(Native Method)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at java.lang.reflect.Method.invoke(Method.java:511)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:786)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at dalvik.system.NativeStart.main(Native Method)
03-11 10:55:58.744: E/AndroidRuntime(27404): Caused by: java.lang.ClassCastException: android.widget.ScrollView cannot be cast to com.demo.listener.ScrollViewExt
03-11 10:55:58.744: E/AndroidRuntime(27404):    at com.example.scrolltest.MainActivity.onCreate(MainActivity.java:21)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.Activity.performCreate(Activity.java:5008)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1079)
03-11 10:55:58.744: E/AndroidRuntime(27404):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2023)
03-11 10:55:58.744: E/AndroidRuntime(27404):    ... 11 more

Answer 1

你有

 <ScrollView  // its a scorllview
    android:id="@+id/scrollTest"

但是当你初始化时，你有

  sv = (ScrollViewExt) findViewById(R.id.scrollTest); 
  // casting to ScrollViewExt which should be ScrollView

如果您在xml中有ScrollView，则将其初始化为

  sv = (ScrollView) findViewById(R.id.scrollTest);

或

  <yourpackagename.ScrollViewExt 
   android:id="@+id/scrollTest"
    android:layout_height="600dp"
    android:layout_width="match_parent">
        <WebView 
            android:id="@+id/webTest"
            android:layout_height="600dp"
            android:layout_width="match_parent"/>
  </yourpackagename.ScrollViewExt >

Answer 2

不必在布局中使用ScrollView，而是必须使元素成为ScrollViewExt的完全命名空间限定名称

 <com.demo.listener.ScrollViewExt
        android:id="@+id/scrollTest"
        android:layout_height="600dp"
        android:layout_width="match_parent">
            <WebView 
                android:id="@+id/webTest"
                android:layout_height="600dp"
                android:layout_width="match_parent"/>
    </com.demo.listener.ScrollViewExt>

Answer 3

尝试替换 ScrollView在您的Xml布局中使用ScrollViewExt

在尝试查看WebView滚动是否已到达时获取ClassCastException

3 个答案: