androidviewflow
ViewFlow & CircleFlowIndicator - Null Pointer Exception
I am using ViewFlow & CircleFlowIndicator to view & show circle to indicate changes in View
Still i am showing same text for each and every View, see below image :
Note:
still showing "Remember Life" in textView1 and "Instantly search memories for friends ......" in textView2
Now i want to show text based on View position, for an example:
If View position is 0 then need to show "TextView - 1.0" in textView1, "TextView - 2.0" in textView2 and if View position is 1 then need to show "TextView - 1.1" in textView1, "TextView - 2.1" in textView2 and so on...
But everytime, I am getting Null Pointer Exception at line number - 35
which is : position = viewFlow.getPositionForView(indic);
How may i know current view Position of ViewFlow ?
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 report:
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>
Solution
Cause of the Exception:
You have added a switch-case in onCreate method for changing the text. This is incorrect. User inputs should be handled by implementing event listeners in Java.
Solution:
Add a listener to the view. When the view is swiped, the listener will handle the event and change the text as per the position.
Add a setOnViewSwitchListener to the view and override the onSwitched method.
Sample Code:
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------
