Question

我在做Google地图应用程序我写了一个函数来查找地址当我在主要活动中编写代码时，它是有效的但是当我写另一个活动时。它总是强制关闭app。

有什么问题以及如何解决？

这是我的日志：

11-24 08:56:52.659: E/AndroidRuntime(16334): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.zzzzzz/com.example.zzzzzz.Direction}: java.lang.NullPointerException

这是我的主要活动代码查找地址：

        // find address
    final Geocoder geocoder = new Geocoder(MainActivity.this);

    final EditText ed = (EditText) findViewById(R.id.edAddress);
    Button btAddress = (Button) findViewById(R.id.btAddress);
    btAddress.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {

            String Ten = ed.getText().toString();
            try {
                List<Address> l = geocoder.getFromLocationName(Ten, 5);
                if (l != null && l.size() > 0) {
                    int lat = (int) (l.get(0).getLatitude() * 1000000);
                    int lon = (int) (l.get(0).getLongitude() * 1000000);
                    GeoPoint pt = new GeoPoint(lat, lon);

                    p = pt;
                    MapOverlay mar = new MapOverlay();
                    listOfOverlays.add(mar);

                    mv.getController().setZoom(17);
                    mv.getController().setCenter(pt);

                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                Log.v("Loi: ", "Loi 1 cua tui ne");
            }
        }
    });

这是我的功能开始其他活动：

public boolean onOptionsItemSelected(MenuItem item) {
    switch(item.getItemId()) {
    case R.id.about:
        //about
        Intent about = new Intent("com.example.zzzzzz.About");
        startActivity(about);
        break;
    case R.id.setting:
        //setting
        Intent setting = new Intent("com.example.zzzzzz.Setting");
        startActivity(setting);
        break;
    case R.id.direction:
        //direction
        Intent direction = new Intent("com.example.zzzzzz.Direction");
        startActivity(direction);
        break;
    case R.id.MyLocation:
        //mylocation
        //Intent mylocation = new Intent("com.example.zzzzzz.MyLocation");
        //startActivity(mylocation);
        initLocationManagerV2();
        LocationManager locationManager;
        locationManager = (LocationManager)getSystemService (Context.LOCATION_SERVICE);
        Location location = locationManager.getLastKnownLocation (LocationManager.GPS_PROVIDER);
        double lat = location.getLatitude();
        double lng = location.getLongitude();
        GeoPoint find = new GeoPoint((int)(lat*1E6), (int)(lng*1E6));
        mv.getController().animateTo(find);
        mv.invalidate();
        break;
    }

    return false;
}

这是我的方向活动：

public class Direction extends Activity {

MainActivity maintest;

@Override
protected void onCreate(Bundle savedInstanceState) {
    // TODO Auto-generated method stub
    super.onCreate(savedInstanceState);
    setContentView(R.layout.direction);

    // find address
    final Geocoder geocoder = new Geocoder(maintest);

    final EditText edMylocation = (EditText) findViewById(R.id.edMylocation);
    final EditText edEndpoint = (EditText) findViewById(R.id.edEndpoint);
    Button btDirection = (Button) findViewById(R.id.btDirection);

    btDirection.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {
            String endpoint = edEndpoint.getText().toString();


            try {
                List<Address> l = geocoder.getFromLocationName(endpoint, 5);
                if (l != null && l.size() > 0) {
                    int lat = (int) (l.get(0).getLatitude() * 1000000);
                    int lon = (int) (l.get(0).getLongitude() * 1000000);
                    GeoPoint pt = new GeoPoint(lat, lon);

                    //p = pt;
                    //MapOverlay mar = new MapOverlay();
                    //listOfOverlays.add(mar);

                    maintest.mv.getController().setZoom(17);
                    //maintest.mv.getController().setCenter(pt);

                }
            } catch (IOException e) {
                // TODO Auto-generated catch block
                Log.v("Loi: ", "Loi 1 cua tui ne");
            }

        }
    });

}

}

////////////////////////////////////// 这是我做的功能（AndylandDev）：

protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    if (requestCode == 1 && resultCode == RESULT_OK) {

        String endpoint = data.getStringExtra("endpoint");
        final Geocoder geocoder = new Geocoder(MainActivity.this);
        try {
            List<Address> l = geocoder.getFromLocationName(endpoint, 5);
            if (l != null && l.size() > 0) {
                int lat = (int) (l.get(0).getLatitude() * 1000000);
                int lon = (int) (l.get(0).getLongitude() * 1000000);
                GeoPoint pt = new GeoPoint(lat, lon);

                p = pt;
                //MapOverlay mar = new MapOverlay();
                //listOfOverlays.add(mar);

                mv.getController().setZoom(17);
                mv.getController().setCenter(pt);

            }
        } catch (IOException e) {
            // TODO Auto-generated catch block
            Log.v("Loi: ", "Loi 1 cua tui ne");
        }
    }
}

Answer 1

所以

new Geocoder(maintest);

可能会抛出NullPointerException，因为你的maintest变量是null。一般来说，活动不应该像这样直接相互访问。这将是正确的方法：

启动方向活动时：

case R.id.direction:
    //direction
    Intent direction = new Intent("com.example.zzzzzz.Direction");
    startActivityForResult(direction, 1);
    break;

在方向活动的onCreate（）

...

btDirection.setOnClickListener(new OnClickListener() {

    public void onClick(View v) {
        Intent intent = new Intent();
        intent.putExtra("endpoint", edEndpoint.getText().toString());
        setResult(RESULT_OK, intent);
        finish();
});

...

然后将此方法添加到MainActivity

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {

if (requestCode == 1 && resultCode == RESULT_OK) {

    String endpoint = data.getStringExtra("endpoint");
    //do whatever with it
}

在另一个活动中查找地址

1 个答案: