Question

我试图在Android中创建自定义视图。我的视图将绘制一些通过addTimelines（）方法传递的时间轴。 Logcat说有一个执行此代码的NullPointerException，调试我注意到onDraw（）方法调用时，ArrayList listaTl为空（其值为null）。

import java.util.ArrayList;
import android.content.Context;
import android.graphics.Canvas;
import android.graphics.Color;
import android.graphics.Paint;
import android.graphics.Rect;
import android.util.AttributeSet;
import android.view.View;

public class TimelineView extends View 
{
    private Paint p;
    private ArrayList<TimelineGrafica> listaTl;

    public TimelineView(Context context, AttributeSet attrs)
    {
        super(context, attrs);
        setVerticalScrollBarEnabled(true);
        setHorizontalScrollBarEnabled(true);
        setMinimumHeight(400);
        if(!isInEditMode())
        {init();}
        init();
    }


    public void addTimelines(ArrayList<TimelineGrafica> tls)
    {
        listaTl = tls;
    }

    private void init()
    {
        this.p = new Paint();
    }

    private void disegnaPunta(Canvas c, Paint p, TimelineGrafica t)
    {
        int[] x = new int[3];
        int[] y = new int[3];

        x[0] = t.getTotaleDurata();
        y[0] = t.getCoordinataY() - 20;

        x[1] = t.getTotaleDurata() + 40;
        y[1] = t.getCoordinataY() + (t.getSpessoreTimeline()/2);

        x[2] = t.getTotaleDurata();
        y[2] = t.getCoordinataY() + t.getSpessoreTimeline() + 20;

        c.drawLine(x[0], y[0], x[1], y[1], p);
        c.drawLine(x[1], y[1], x[2], y[2], p);
        c.drawLine(x[0], y[0], x[2], y[2], p);
    }

    private void disegnaRettangolo(Canvas c, Paint p, TimelineGrafica t)
    {
        Rect r = new Rect(t.getCoordinataX(), 
                          t.getCoordinataY(), 
                          t.getTotaleDurata(), 
                          t.getCoordinataY() + 
                          t.getSpessoreTimeline());
        c.drawRect(r, p);
    }

    private void disegnaGrain(Canvas c, Paint p, TimelineGrafica t)
    {
        //Calcolo il 5% di distanza dalla punta
        int numeroFatti = (t.getTotaleDurata() - 
                           (t.getTotaleDurata()*3/100))/
                            t.getDistanzaIntervalli();
        for(int i=0, cX = t.getCoordinataX(); i<numeroFatti; 
                    i++, cX += t.getDistanzaIntervalli())
        {
            c.drawLine(cX, t.getCoordinataY() - 20, cX,
                        t.getCoordinataY() + t.getSpessoreTimeline() + 20, p);
            if(i<=9)
                c.drawText(""+i, cX-3, t.getCoordinataY() + 
                        t.getSpessoreTimeline() + 35, p);
            else
                c.drawText(""+i, cX-5, t.getCoordinataY() + 
                        t.getSpessoreTimeline() + 35, p);               
        }
    }

    @Override
    public void onDraw(Canvas canvas)
    {
        if(!listaTl.isEmpty())
            for(TimelineGrafica t : listaTl)
            {
                canvas.drawColor(Color.GRAY);           
                p.setColor(t.getColor());
                p.setStyle(Paint.Style.FILL_AND_STROKE); 
                p.setAntiAlias(true);   
                p.setStrokeWidth(1);
                disegnaGrain(canvas,p,t);
                disegnaRettangolo(canvas,p,t);
                disegnaPunta(canvas,p,t);
            }
    }   
}

在这里，我调用方法添加一个新的时间轴来绘制。

protected void onCreate(Bundle savedInstanceState) 
{
    super.onCreate(savedInstanceState);
    ArrayList<TimelineGrafica> tl = new ArrayList<TimelineGrafica>();

    this.disegnoTimeline = new TimelineView(this, null);

    PlainTimeLine tlp = ottieniTimeline("Timeline1.txt");
    TimelineGrafica tlpp = new TimelineGrafica(tlp, 10, 30, 20, Color.WHITE); 

    tl.add(tlpp);
    this.disegnoTimeline.addTimelines(tl);  

    setContentView(R.layout.timeline_view);
}

如果我在addTimelines（）之后调用postInvalidate（）/ invalidate（）方法，问题就出现了。

有谁知道问题出在哪？

Answer 1

方法postInvalidate（）或invalidate（），当它被调用时，方法onDraw（）将被调用因此，当您更改TimelineView（如addTimelines（ArrayList））时，应使用postInvalidate（）或invalidate（）

刷新自身

Android中的onDraw（）方法有问题

1 个答案: