Question

我有一个使用此代码的Nullpointer Exception，之前它已经很清楚了。异常显示在 mainLayout.setOnTouchListener（this），但我不会理解为什么。在另一个活动中更改了一些代码。：

public class Assistantbuilder extends Activity implements OnTouchListener
{
    private ViewFlipper flipper = null;
    private float fromPosition;

    @Override
    public void onCreate(Bundle savedInstanceState)
    {
        super.onCreate(savedInstanceState);
        requestWindowFeature(Window.FEATURE_NO_TITLE);
        setContentView(R.layout.main);

        LinearLayout mainLayout = (LinearLayout) findViewById(R.id.main_layout);
        mainLayout.setOnTouchListener(this);

        flipper = (ViewFlipper) findViewById(R.id.flipper);

        LayoutInflater inflater = (LayoutInflater)         getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        int layouts[] = new int[]{ R.layout.dashboard_layout, R.layout.dashboard_layout2, R.layout.dashboard_layout3, R.layout.dashboard_layout4 };
        for (int layout : layouts)
            flipper.addView(inflater.inflate(layout, null));

        Button btndimensions_rafters = (Button) findViewById(R.id.home_btn_dimensions_rafters);
        btndimensions_rafters.setOnClickListener(new View.OnClickListener() {
            public void onClick(View arg0) {
                switch (arg0.getId()) {
                case R.id.home_btn_dimensions_rafters:
                    Intent i = new Intent(Assistantbuilder.this,
                            dimensions_rafters.class);
                    startActivity(i);
                    break;
                }
            }
        });
        Button btngable_roof = (Button) findViewById(R.id.home_btn_gable_roof);
        btngable_roof.setOnClickListener(new View.OnClickListener() {
            public void onClick(View arg0) {
                switch (arg0.getId()) {
                case R.id.home_btn_gable_roof:
                    Intent i = new Intent(Assistantbuilder.this,
                            GableRoof.class);
                    startActivity(i);
                    break;
                }
            }
        });

    }

可能在这里有些错误：

    public boolean onTouch(View view, MotionEvent event)
    {
        switch (event.getAction())
        {
        case MotionEvent.ACTION_DOWN:
            fromPosition = event.getX();
            break;
        case MotionEvent.ACTION_UP:
            float toPosition = event.getX();
            if (fromPosition > toPosition)
            {
                flipper.setInAnimation(AnimationUtils.loadAnimation(this,R.anim.go_next_in));
                flipper.setOutAnimation(AnimationUtils.loadAnimation(this,R.anim.go_next_out));
                flipper.showNext();
            }
            else if (fromPosition < toPosition)
            {
                flipper.setInAnimation(AnimationUtils.loadAnimation(this,R.anim.go_prev_in));
                flipper.setOutAnimation(AnimationUtils.loadAnimation(this,R.anim.go_prev_out));
                flipper.showPrevious();
            }
        default:
            break;
        }
        return true;
    }
}

非常感谢。

Answer 1

好吧，如果该行位于您的活动的onCreate中，this应始终有效，因此唯一可以为null的其他内容是mainLayout。您是否更改了XML布局文件？运行时找不到标识为LinearLayout的{{1}}。

Nullpointer异常setOnTouchListener（this）

1 个答案: