how to use custom views in layout xml

2019-05-27 12:43发布

站内文章 / Android
11 0 0

问题:

I've created a custom layout to show gif animated image. Here is the code: 

public class GIFView extends View{        
private Movie movie;  
private InputStream is;  
private long moviestart;  
private long duration;

public GIFView(Context context) {  
    super(context);
    is=getResources().openRawResource(R.drawable.anim_cerca);  
    movie=Movie.decodeStream(is);
    duration = movie.duration();
}  

public GIFView(Context context,AttributeSet set){
    super(context,set);
    is=getResources().openRawResource(R.drawable.anim_cerca);  
    movie=Movie.decodeStream(is);
    duration = movie.duration();
}

public GIFView(Context context,AttributeSet set,int def){
    super(context,set,def);
    is=getResources().openRawResource(R.drawable.anim_cerca);  
    movie=Movie.decodeStream(is);
    duration = movie.duration();
}

@Override  
protected void onDraw(Canvas canvas) {
    super.onDraw(canvas);
    long now=android.os.SystemClock.uptimeMillis();
    Paint p = new Paint();
    p.setAntiAlias(true);
    if (moviestart == 0) 
        moviestart = now;

    int relTime = (int)((now - moviestart) % duration);

    movie.setTime(relTime);
    movie.draw(canvas,0,0);


    this.invalidate();
}                         
}

This is the xml where i put this object: 

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
android:orientation="vertical" android:layout_width="match_parent"
android:layout_height="match_parent" android:background="@drawable/sfondo">
<LinearLayout android:id="@+id/linearLayout2"
    android:layout_height="wrap_content" android:layout_width="match_parent"
    android:orientation="vertical">
    <LinearLayout android:id="@+id/linearLayout1"
        android:layout_height="fill_parent" android:weightSum="1"
        android:layout_width="fill_parent" android:orientation="horizontal">
        <ImageView android:layout_height="73dp" android:id="@+id/imageView1"
            android:layout_weight="0.25" android:src="@drawable/trovachiavi"
            android:layout_width="256dip"></ImageView>
        <ImageButton android:id="@+id/infoButton"
            android:background="@null" android:layout_height="47dp"
            android:layout_marginLeft="10dip" android:layout_weight="0.25"
            android:layout_marginTop="15dip" android:src="@drawable/info_mini"
            android:layout_width="47dp"></ImageButton>
    </LinearLayout>
</LinearLayout>
<LinearLayout android:id="@+id/layoutGIF"
    android:layout_height="wrap_content" android:layout_width="wrap_content"
    android:orientation="vertical">
    <com.digit.GIFView android:id="@+id/gIFView1"
        android:layout_width="wrap_content" android:layout_height="wrap_content"
        android:layout_gravity="center"></com.digit.GIFView>
</LinearLayout>
<ImageButton android:id="@+id/avvia_cerca"
    android:layout_height="wrap_content" android:layout_width="wrap_content"
    android:layout_marginTop="10dp" android:layout_gravity="center|bottom"
    android:background="@null"></ImageButton>
</LinearLayout>

When i go in the Graphical Layout zone of xml, it appears an error:

The following classes could not be instantiated:
-  (Open Class, Show Error Log)
See the Error Log (Window > Show View) for more details.
Tip: Use View.isInEditMode() in your custom views to skip code when shown in Eclipse

and in Error log appears these:

java.lang.NullPointerException
at com.digit.GIFView.<init>(GIFView.java:27)
at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:39)
at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:27)
at java.lang.reflect.Constructor.newInstance(Constructor.java:513)
at com.android.ide.eclipse.adt.internal.editors.layout.ProjectCallback.instantiateClass(ProjectCallback.java:396)
at com.android.ide.eclipse.adt.internal.editors.layout.ProjectCallback.loadView(ProjectCallback.java:164)
at com.android.layoutlib.bridge.android.BridgeInflater.loadCustomView(BridgeInflater.java:205)
at com.android.layoutlib.bridge.android.BridgeInflater.createViewFromTag(BridgeInflater.java:133)
at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:83)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:702)
at android.view.LayoutInflater_Delegate.rInflate(LayoutInflater_Delegate.java:86)
at android.view.LayoutInflater.rInflate(LayoutInflater.java:702)
at android.view.LayoutInflater.inflate(LayoutInflater.java:479)
at android.view.LayoutInflater.inflate(LayoutInflater.java:367)
at com.android.layoutlib.bridge.impl.RenderSessionImpl.inflate(RenderSessionImpl.java:324)
at com.android.layoutlib.bridge.Bridge.createSession(Bridge.java:321)
at com.android.ide.common.rendering.LayoutLibrary.createSession(LayoutLibrary.java:325)
at com.android.ide.eclipse.adt.internal.editors.layout.gle2.RenderService.createRenderSession(RenderService.java:380)
at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.renderWithBridge(GraphicalEditorPart.java:1310)
at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.recomputeLayout(GraphicalEditorPart.java:1075)
at com.android.ide.eclipse.adt.internal.editors.layout.gle2.GraphicalEditorPart.activated(GraphicalEditorPart.java:901)
at com.android.ide.eclipse.adt.internal.editors.layout.LayoutEditor.partActivated(LayoutEditor.java:416)
at com.android.ide.eclipse.adt.internal.editors.layout.LayoutEditor.partBroughtToTop(LayoutEditor.java:425)
at org.eclipse.ui.internal.PartListenerList$2.run(PartListenerList.java:87)
at org.eclipse.core.runtime.SafeRunner.run(SafeRunner.java:42)
at org.eclipse.core.runtime.Platform.run(Platform.java:888)
at org.eclipse.ui.internal.PartListenerList.fireEvent(PartListenerList.java:57)
at org.eclipse.ui.internal.PartListenerList.firePartBroughtToTop(PartListenerList.java:85)
at org.eclipse.ui.internal.PartService.firePartBroughtToTop(PartService.java:208)
at org.eclipse.ui.internal.WorkbenchPagePartList.firePartBroughtToTop(WorkbenchPagePartList.java:76)
at org.eclipse.ui.internal.WorkbenchPagePartList.fireActiveEditorChanged(WorkbenchPagePartList.java:52)
at org.eclipse.ui.internal.PartList.setActiveEditor(PartList.java:162)
at org.eclipse.ui.internal.WorkbenchPage.makeActiveEditor(WorkbenchPage.java:1281)
at org.eclipse.ui.internal.WorkbenchPage.setActivePart(WorkbenchPage.java:3530)
at org.eclipse.ui.internal.WorkbenchPage.requestActivation(WorkbenchPage.java:3077)
at org.eclipse.ui.internal.PartPane.requestActivation(PartPane.java:279)
at org.eclipse.ui.internal.EditorPane.requestActivation(EditorPane.java:98)
at org.eclipse.ui.internal.PartPane.setFocus(PartPane.java:325)
at org.eclipse.ui.internal.EditorPane.setFocus(EditorPane.java:127)
at org.eclipse.ui.internal.PartStack.presentationSelectionChanged(PartStack.java:844)
at org.eclipse.ui.internal.PartStack.access$1(PartStack.java:827)
at org.eclipse.ui.internal.PartStack$1.selectPart(PartStack.java:137)
at org.eclipse.ui.internal.presentations.util.TabbedStackPresentation$1.handleEvent(TabbedStackPresentation.java:133)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.fireEvent(AbstractTabFolder.java:269)
at org.eclipse.ui.internal.presentations.util.AbstractTabFolder.fireEvent(AbstractTabFolder.java:278)
at org.eclipse.ui.internal.presentations.defaultpresentation.DefaultTabFolder.access$1(DefaultTabFolder.java:1)
at org.eclipse.ui.internal.presentations.defaultpresentation.DefaultTabFolder$2.handleEvent(DefaultTabFolder.java:88)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:3783)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1375)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1398)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1383)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1195)
at org.eclipse.swt.custom.CTabFolder.setSelection(CTabFolder.java:2743)
at org.eclipse.swt.custom.CTabFolder.onMouse(CTabFolder.java:1429)
at org.eclipse.swt.custom.CTabFolder$1.handleEvent(CTabFolder.java:257)
at org.eclipse.swt.widgets.EventTable.sendEvent(EventTable.java:84)
at org.eclipse.swt.widgets.Display.sendEvent(Display.java:3783)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1375)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1398)
at org.eclipse.swt.widgets.Widget.sendEvent(Widget.java:1383)
at org.eclipse.swt.widgets.Widget.notifyListeners(Widget.java:1195)
at org.eclipse.swt.widgets.Display.runDeferredEvents(Display.java:3629)
at org.eclipse.swt.widgets.Display.readAndDispatch(Display.java:3284)
at org.eclipse.ui.internal.Workbench.runEventLoop(Workbench.java:2640)
at org.eclipse.ui.internal.Workbench.runUI(Workbench.java:2604)
at org.eclipse.ui.internal.Workbench.access$4(Workbench.java:2438)
at org.eclipse.ui.internal.Workbench$7.run(Workbench.java:671)
at org.eclipse.core.databinding.observable.Realm.runWithDefault(Realm.java:332)
at org.eclipse.ui.internal.Workbench.createAndRunWorkbench(Workbench.java:664)
at org.eclipse.ui.PlatformUI.createAndRunWorkbench(PlatformUI.java:149)
at org.eclipse.ui.internal.ide.application.IDEApplication.start(IDEApplication.java:115)
at org.eclipse.equinox.internal.app.EclipseAppHandle.run(EclipseAppHandle.java:196)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.runApplication(EclipseAppLauncher.java:110)
at org.eclipse.core.runtime.internal.adaptor.EclipseAppLauncher.start(EclipseAppLauncher.java:79)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:369)
at org.eclipse.core.runtime.adaptor.EclipseStarter.run(EclipseStarter.java:179)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at org.eclipse.equinox.launcher.Main.invokeFramework(Main.java:620)
at org.eclipse.equinox.launcher.Main.basicRun(Main.java:575)
at org.eclipse.equinox.launcher.Main.run(Main.java:1408)

What can i do? where does the error born? The elements under my custom view aren't displayed!

回答1:

You have a NullPointerException in one of your constructors. I can not exactly tell which one, as the StackTrace says line 27, which is an empty line in the code you posted.

You should re-run your code, check the first line of the stack trace in your code. I would guess it's this line: 

duration = movie.duration();

and the movie object is null.



回答2:

The problem is not with your code but displaying custom view in Graphical Layout. Drawing views rely on device features. To see your custom view properly you have to use the isInEditMode() method in your custom view implementation. Based on that method, you have to implement alternative initialization and drawing.



回答3:

I think you want your xml file object to be like this:

<com.spazio.digitale.GIFView android:id="@+id/gIFView1"
    android:layout_width="wrap_content" android:layout_height="wrap_content"
    android:layout_gravity="center" />

assuming that your package is com.spazio.digitale which I'm not totally sure of from what you've posted.



回答4:

Try this it work for me 

public class MyOwnTextView extends TextView {

    public MyOwnTextView(Context context, AttributeSet attrs, int defStyle) {
        super(context, attrs, defStyle);
        // TODO Auto-generated constructor stub

    }

    public MyOwnTextView(Context context, AttributeSet attrs) {
        super(context, attrs);
        // TODO Auto-generated constructor stub

    }
    public MyOwnTextView(Context context) {
        super(context);
        // TODO Auto-generated constructor stub

    }

    public void setTypeface(Typeface tf, int style) {
        if(!this.isInEditMode()){
        Typeface normalTypeface = Typeface.createFromAsset(getContext().getAssets(), "font/Roboto-Light.ttf");
        Typeface boldTypeface = Typeface.createFromAsset(getContext().getAssets(), "font/Roboto-Light.ttf");

        if (style == Typeface.BOLD) {
            super.setTypeface(boldTypeface/*, -1*/);
        } else {
            super.setTypeface(normalTypeface/*, -1*/);
        }
        }

    }   

}

then at the xml 

<com.xxxxx.appname.MyOwnTextView

          android:layout_width="fill_parent"
          android:layout_height="fill_parent"

        />


回答5:

My problem was that a ttf font was placed in custom "fonts" folder under assets folder. Error when displayed xml layout:

The following classes could not be instantiated:
----
Tip: Use View.isInEditMode() in your custom views to skip code when shown...

Then, I placed the font under root assets folder, rebuilt project and, magically, all works and the xml layout was showed ok.

Then, I dragged the font to the "fonts" folder again trough ide, rebuilt project and the xml layout remains showed ok.

I don´t have any idea why this operation worked but if it can help anyone, ok.



标签： android xml layout custom-view
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