ImageView findViewById和setContent(R.layout.main)不起作用

Question

我对这个简单的代码有疑问.我正在尽一切可能,但setContent(R.layout.main)总是会导致错误.如果我尝试调试代码svgView =(SVGView),则findViewById(R.id.svgview)值始终为null.

这是我的代码:

SVGViewActivity.java:

    package android.svgview;

    import com.larvalabs.svgandroid.SVG;
    import com.larvalabs.svgandroid.SVGParser;

    import android.app.Activity;
    import android.graphics.Color;
    import android.os.Bundle;

    public class SVGViewActivity extends Activity {
        /** Called when the activity is first created. */

    private SVGView svgView;
    private ViewListener viewListener;
    private ViewState viewState;
    private SVG svg;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.main);
        svgView = (SVGView)findViewById(R.id.svgview);
        viewListener = new ViewListener();
        viewState = new ViewState();

        svgView.setViewState(viewState);
        svgView.setOnTouchListener(viewListener);
        viewListener.setViewState(viewState);

        svg = SVGParser.getSVGFromResource(getResources(), R.drawable.android);
        svgView.setImageDrawable(svg.createPictureDrawable());
        svgView.setBackgroundColor(Color.WHITE);

    }
}

SVGView.java

package android.svgview;

import java.util.Observable;
import java.util.Observer;

import android.content.Context;
import android.graphics.Canvas;
import android.widget.ImageView;

public class SVGView extends ImageView implements Observer {

    private ViewState viewState;

    public SVGView(Context context) {
        super(context);
    }

    public void setViewState(ViewState viewState){
        if(this.viewState==null){
            this.viewState = viewState;
            this.viewState.addObserver(this);
        }
    }

    protected void onDraw(Canvas canvas){

        canvas.scale(1.0f, 1.0f);
        canvas.translate(viewState.getX(), viewState.getY());

        super.onDraw(canvas);

    }
    public void update(Observable observable, Object data) {
        invalidate();

    }
}

和main.xml

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

    <android.svgview.SVGView
        android:id="@+id/svgview" 
        />
</LinearLayout>

当我改变svgView = (SVGView)findViewById(R.id.svgview);了svgView = new SVGView(this);,然后setContentView(R.layout.main);为setContentView(svgView);一切工作正常.但是使用main.xml会导致错误.

我尝试了清理并重新编译项目,在新的eclipse安装中编译它所有更新但没有效果.我不知道问题出在哪里: - /

Answer 1

您可能需要在以下内容中提供此构造函数SVGView.java:

public SVGView(Context context AttributeSet atrs ) {
    super(context, atrs);
}

然后将xml文件中的声明更改为:

<android.svgview.SVGView
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:id="@+id/svgview" />