android - ViewFlow 和 CircleFlowIndicator - 空指针异常

Question

我正在使用 ViewFlow & CircleFlowIndicator至 view & show圈到indicate View 的变化

还是我showing same text对于每一个View ，见下图:

注意:

仍在 textView1 中显示“Remember Life”，在 textView2 中显示“Instantly search memories for friends ......”

现在我想根据View position显示文本 , 对于 example :

如果查看position为0则需要在textView1中显示“TextView - 1.0”，在textView2中显示“TextView - 2.0”，如果View position是1 那么需要在textView1 中显示“TextView - 1.1”，在textView2 中显示“TextView - 2.1”和so on ...

但每次，我都会得到 Null Pointer Exception在 line number - 35

即:position = viewFlow.getPositionForView(indic);

我如何知道 ViewFlow 的当前 View 位置？

MainActivity.java:-

public class MainActivity extends Activity {

    private ViewFlow viewFlow;
    TextView textView1, textView2;
    int position = 0;

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setTitle(R.string.circle_title);
        setContentView(R.layout.screen_layout);

        viewFlow = (ViewFlow) findViewById(R.id.viewflow);
        viewFlow.setAdapter(new ImageAdapter(this), 1); // default focus on second circle

        CircleFlowIndicator indic = (CircleFlowIndicator) findViewById(R.id.viewflowindic);
        viewFlow.setFlowIndicator(indic);       

        textView1 = (TextView) findViewById(R.id.textView1);
        textView2 = (TextView) findViewById(R.id.textView2);

        position = viewFlow.getPositionForView(indic);
        Toast.makeText(MainActivity.this, position, Toast.LENGTH_LONG).show();

        switch (position) {
        case 0:
            textView1.setText("TextView - 1.0"); // TextView - 1, position - 0
            textView2.setText("TextView - 2.0"); // TextView - 2, position - 0
            break;

        case 1:
            textView1.setText("TextView - 1.1");
            textView2.setText("TextView - 2.1");
            break;

        case 2:
            textView1.setText("TextView - 1.2");
            textView2.setText("TextView - 2.2");
            break;

        case 3:
            textView1.setText("TextView - 1.3");
            textView2.setText("TextView - 2.3");
            break;

        case 4:
            textView1.setText("TextView - 1.4");
            textView2.setText("TextView - 2.4");
            break;

        default:

            break;
        }

    }

    /* If your min SDK version is < 8 you need to trigger the onConfigurationChanged in ViewFlow manually, like this */ 
    @Override
    public void onConfigurationChanged(Configuration newConfig) {
        super.onConfigurationChanged(newConfig);
        viewFlow.onConfigurationChanged(newConfig); 
    }
}

Logcat 报告:

08-22 06:54:53.811: W/dalvikvm(1829): threadid=1: thread exiting with uncaught exception (group=0x41465700)
08-22 06:54:53.840: E/AndroidRuntime(1829): FATAL EXCEPTION: main
08-22 06:54:53.840: E/AndroidRuntime(1829): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.indianic.viewflipperdemo/com.indianic.viewflipperdemo.CircleViewFlipperActivity}: java.lang.NullPointerException
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2211)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2261)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.app.ActivityThread.access$600(ActivityThread.java:141)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1256)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.os.Handler.dispatchMessage(Handler.java:99)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.os.Looper.loop(Looper.java:137)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.app.ActivityThread.main(ActivityThread.java:5103)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at java.lang.reflect.Method.invokeNative(Native Method)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at java.lang.reflect.Method.invoke(Method.java:525)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:737)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:553)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at dalvik.system.NativeStart.main(Native Method)
08-22 06:54:53.840: E/AndroidRuntime(1829): Caused by: java.lang.NullPointerException
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.widget.AdapterView.getPositionForView(AdapterView.java:597)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at com.indianic.viewflipperdemo.CircleViewFlipperActivity.onCreate(CircleViewFlipperActivity.java:35)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.app.Activity.performCreate(Activity.java:5133)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1087)
08-22 06:54:53.840: E/AndroidRuntime(1829):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2175)
08-22 06:54:53.840: E/AndroidRuntime(1829):     ... 11 more

XML:-

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    xmlns:app="http://schemas.android.com/apk/res/com.indianic.viewflipperdemo"
    android:layout_width="fill_parent"
    android:layout_height="fill_parent"
    android:orientation="vertical" >

     <com.indianic.viewflipperdemo.widget.ViewFlow
        android:id="@+id/viewflow"
        android:layout_width="fill_parent"
        android:layout_height="fill_parent"
        app:sidebuffer="3" >
    </com.indianic.viewflipperdemo.widget.ViewFlow>

    <ImageView
        android:id="@+id/imageView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="30dp"
        android:src="@drawable/ic_launcher" />

    <TextView
        android:id="@+id/textView1"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/textView2"
        android:layout_centerHorizontal="true"
        android:text="Remember Life"
        android:textAppearance="?android:attr/textAppearanceMedium"
        android:textStyle="bold" />

    <TextView
        android:id="@+id/textView2"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/viewflowindic"
        android:layout_centerHorizontal="true"
        android:layout_marginLeft="30dp"
        android:layout_marginRight="30dp"
        android:padding="5dp"
        android:text="Instantly search memories of friends, season, birthdays, and more"
        android:textAppearance="?android:attr/textAppearanceSmall" />

    <LinearLayout
        android:id="@+id/linearLayout1"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_alignParentBottom="true"
        android:layout_alignParentLeft="true"
        android:orientation="horizontal"
        android:paddingBottom="10dp"
        android:paddingLeft="20dp"
        android:paddingRight="20dp"
        android:paddingTop="10dp" >

        <Button
            android:id="@+id/textView"
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_gravity="left|center"
            android:layout_weight="1"
            android:text="Register"
            android:textColor="#000000" />

        <Button
            android:layout_width="0dp"
            android:layout_height="wrap_content"
            android:layout_gravity="right"
            android:layout_weight="1"
            android:text="Login"
            android:textColor="#000000" />
    </LinearLayout>

    <com.indianic.viewflipperdemo.widget.CircleFlowIndicator
        android:id="@+id/viewflowindic"
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:layout_above="@+id/linearLayout1"
        android:layout_centerHorizontal="true"
        android:padding="20dp"
        app:inactiveType="stroke" />

</RelativeLayout>

Answer 1

异常原因:

您在 onCreate 方法中添加了一个 switch-case 来更改文本。这是不正确的。用户输入应由 implementing event listeners in Java 处理.

解决方案:

向 View 添加一个监听器。当滑动 View 时，监听器将处理事件并根据位置更改文本。

在 View 中添加一个setOnViewSwitchListener并覆盖onSwitched方法。

示例代码:

viewFlow.setOnViewSwitchListener(new ViewSwitchListener() {
    public void onSwitched(View v, int position) {
        //position is received as an argument from the system, it doesn't need to be calculated
        switch (position) {
        case 0:
            textView1.setText("TextView - 1.0"); // TextView - 1,
                                                    // position - 0
            textView2.setText("TextView - 2.0"); // TextView - 2,
                                                    // position - 0
            break;
            // ----rest of your code here------

引用资料:

• https://github.com/pakerfeldt/android-viewflow