java - 无法 Intent 与另一个 Activity 正常工作

Question

我正在制作一个多 Activity 应用程序，我制作的前两个 Activity 运行良好，没有强制关闭，但是一旦我添加了第三个 Activity ，一个用于注册显示屏上的触摸，当单击其列表项时，我得到强制关闭。

我所做的与其他 Activity 完全相同，但根本不知道出了什么问题，所有 Activity 也都包含在 AndroidManifest 文件中。

ListView 的主要 Activity :

public class MyCustomAdapter extends ArrayAdapter<String> {

    public MyCustomAdapter(Context context, int textViewResourceId, String[] objects) {
        super(context, textViewResourceId, objects);
        // TODO Auto-generated constructor stub
    }

    @Override
    public View getView(int position, View convertView, ViewGroup parent) {
        // TODO Auto-generated method stub
        //return super.getView(position, convertView, parent);
        LayoutInflater inflater = getLayoutInflater();
        View row = inflater.inflate(R.layout.row, parent, false);
        TextView label = (TextView)row.findViewById(R.id.tool);
        label.setText(Tool[position]);
        ImageView icon = (ImageView)row.findViewById(R.id.icon);

        if (Tool[position]=="Random # Generator") {
            icon.setImageResource(R.drawable.generator);
        }
        else if (Tool[position]=="Converter"){
            icon.setImageResource(R.drawable.converter);
        }
        else if (Tool[position]=="Ruler"){
            icon.setImageResource(R.drawable.ruler);
        }
        else if (Tool[position]=="Stopwatch"){
            icon.setImageResource(R.drawable.stopwatch);
        }
        else if (Tool[position]=="Countdown"){
            icon.setImageResource(R.drawable.countdown);
        }
        else if (Tool[position]=="Multitouch"){
            icon.setImageResource(R.drawable.touch);
        }

        return row;
        }
    }

    String[] Tool = {"Stopwatch", "Countdown", "Multitouch", "Ruler", "Converter", "Random # Generator"};

    /** Called when the activity is first created. */
    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        //setContentView(R.layout.main);
        /*setListAdapter(new ArrayAdapter<String>(this, R.layout.row, R.id.weekofday, DayOfWeek));*/
        setListAdapter(new MyCustomAdapter(this, R.layout.row, Tool));
    }

    @Override
    protected void onListItemClick(ListView l, View v, int position, long id) {
        // TODO Auto-generated method stub
        // super.onListItemClick(l, v, position, id);
        switch(position) {

        case 0:
            Intent stopwatch = new Intent(UsefulToolsActivity.this, Stopwatch.class);
            startActivity(stopwatch);
            return;

        case 1:
            Intent countdown = new Intent(UsefulToolsActivity.this, CountdownActivity.class);
            startActivity(countdown);
            return;

        case 2:
            Intent multitouch = new Intent(UsefulToolsActivity.this, Multitouch.class);
            startActivity(multitouch);
            return;

        default:                    
    }
}

导致强制关闭的 Activity :

public class Multitouch extends View {

private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

final int MAX_NUMBER_OF_POINT = 10;
float[] x = new float[MAX_NUMBER_OF_POINT];
float[] y = new float[MAX_NUMBER_OF_POINT];
boolean[] touching = new boolean[MAX_NUMBER_OF_POINT];

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

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

public Multitouch(Context context) {
    super(context);
    init();
}

void init() {
    paint.setStyle(Paint.Style.STROKE);
    paint.setStrokeWidth(1);
    paint.setColor(Color.BLUE);
}

@Override
protected void onDraw(Canvas canvas) {

    for(int i = 0; i < MAX_NUMBER_OF_POINT; i++) {
        if(touching[i]){
            canvas.drawCircle(x[i], y[i], 50f, paint);
        }
    }
}

@Override
protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    // TODO Auto-generated method stub
    setMeasuredDimension(MeasureSpec.getSize(widthMeasureSpec), 
            MeasureSpec.getSize(heightMeasureSpec));
}

@Override
public boolean onTouchEvent(MotionEvent event) {
    int action = (event.getAction() & MotionEvent.ACTION_MASK);
    int pointCount = event.getPointerCount();

    for (int i = 0; i < pointCount; i++) {
        int id = event.getPointerId(i);

        //Ignore pointer higher than our max.
        if(id < MAX_NUMBER_OF_POINT) {
            x[id] = (int)event.getX(i);
            y[id] = (int)event.getY(i);

            if((action == MotionEvent.ACTION_DOWN)
                    ||(action == MotionEvent.ACTION_POINTER_DOWN)
                    ||(action == MotionEvent.ACTION_MOVE)) {
                touching[id] = true;
            }
            else {
                touching[id] = false;
            }
        } 
    }
    invalidate(); 
    return true;
}

来自 LOGCAT 的信息:

01-02 16:08:05.292: W/dalvikvm(20683): threadid=1: thread exiting with uncaught exception (group=0x40a321f8) 01-02 16:08:05.302: E/AndroidRuntime(20683): FATAL EXCEPTION: main 01-02 16:08:05.302: E/AndroidRuntime(20683): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.reddicliffe.usefultools/com.reddicliffe.usefultools.Multitouch}: java.lang.InstantiationException: can't instantiate class com.reddicliffe.usefultools.Multitouch; no empty constructor 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1880) 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981) 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.app.ActivityThread.access$600(ActivityThread.java:123) 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147) 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.os.Handler.dispatchMessage(Handler.java:99) 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.os.Looper.loop(Looper.java:137) 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.app.ActivityThread.main(ActivityThread.java:4424) 01-02 16:08:05.302: E/AndroidRuntime(20683): at java.lang.reflect.Method.invokeNative(Native Method) 01-02 16:08:05.302: E/AndroidRuntime(20683): at java.lang.reflect.Method.invoke(Method.java:511) 01-02 16:08:05.302: E/AndroidRuntime(20683): at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:784) 01-02 16:08:05.302: E/AndroidRuntime(20683): at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:551) 01-02 16:08:05.302: E/AndroidRuntime(20683): at dalvik.system.NativeStart.main(Native Method) 01-02 16:08:05.302: E/AndroidRuntime(20683): Caused by: java.lang.InstantiationException: can't instantiate class com.reddicliffe.usefultools.Multitouch; no empty constructor 01-02 16:08:05.302: E/AndroidRuntime(20683): at java.lang.Class.newInstanceImpl(Native Method) 01-02 16:08:05.302: E/AndroidRuntime(20683): at java.lang.Class.newInstance(Class.java:1319) 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.app.Instrumentation.newActivity(Instrumentation.java:1023) 01-02 16:08:05.302: E/AndroidRuntime(20683): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1871) 01-02 16:08:05.302: E/AndroidRuntime(20683): ... 11 more

修改多点触控代码

public class Multitouch extends Activity {

public class MultitouchView extends View {

    private Paint paint = new Paint(Paint.ANTI_ALIAS_FLAG);

Answer 1

简而言之:在您的情况下，Multitouch 正在扩展 View 而不是 Activity 类。

如果您想将多点触控显示为 Activity 的内容。

将其用作View，并使用 xml 布局将其添加到 Activity 的 contentView 中，或者只需调用 setContentView(anyMultitouchInstance) ;