Question

我有一个tabHost MainActivity和两个A，B活动。在每个选项卡中，我想将名为cityName的字符串从MainActivity传输到A活动。但我总是在Logcat中得到一个NullPointerException并被强制关闭T.T

这是我的代码：

public class MainActivity extends TabActivity {

private static TabHost tabHost;
public static String selectedCity;
Bundle selectedCityBundle = new Bundle();
Intent selectedCityIntent = new Intent();


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    Resources res = getResources();
    selectedCityBundle.putString("CityName", "LA");
    selectedCityIntent.setClass(this, A.class);
    selectedCityIntent.putExtras(selectedCityBundle);
    tabHost = getTabHost();     
    TabHost.TabSpec spec;
    Intent intent;
    intent = new Intent().setClass(this, A.class);
    spec = tabHost.newTabSpec("tab1")
            .setIndicator("A", res.getDrawable(R.drawable.start))
            .setContent(intent);
    tabHost.addTab(spec);

    intent = new Intent().setClass(this, B.class);
    spec = tabHost.newTabSpec("tab2")
            .setIndicator("B", res.getDrawable(R.drawable.weather))
            .setContent(intent);
    tabHost.addTab(spec);


    tabHost.setCurrentTab(0);

}

A类

public class A extends Activity {

TextView tempNum, cn1, cn2, cn3, ln1, ln2, ln3, city, rainProb;
Intent cityIntent = new Intent();
Bundle cityBundlecityBundle = cityIntent.getExtras();

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.start);
    tempNum = (TextView) findViewById(R.id.temp);
    rainProb = (TextView) findViewById(R.id.raining);
    cn1 = (TextView) findViewById(R.id.zone1News1);
    cn2 = (TextView) findViewById(R.id.zone1News2);
    cn3 = (TextView) findViewById(R.id.zone1News3);
    ln1 = (TextView) findViewById(R.id.zone2News1);
    ln2 = (TextView) findViewById(R.id.zone2News2);
    ln3 = (TextView) findViewById(R.id.zone2News3);
    city = (TextView) findViewById(R.id.location);      
    city.setText(cityBundle.getString("CityName"));
    //Always got error NullPointerException here
}

}

Answer 1

您目前正在将捆绑包放入另一个捆绑包中。将您的城市名称改为：

selectedCityIntent.putExtra("CityName", "LA");

你的代码应运行良好。

修改

您也没有捕获意图，只需在代码中创建一个新意图。在你的A班，得到这样的包：

Bundle cityBundle; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.start); cityBundle = getIntent().getExtras(); tempNum = (TextView) findViewById(R.id.temp); rainProb = (TextView) findViewById(R.id.raining); cn1 = (TextView) findViewById(R.id.zone1News1); cn2 = (TextView) findViewById(R.id.zone1News2); cn3 = (TextView) findViewById(R.id.zone1News3); ln1 = (TextView) findViewById(R.id.zone2News1); ln2 = (TextView) findViewById(R.id.zone2News2); ln3 = (TextView) findViewById(R.id.zone2News3); city = (TextView) findViewById(R.id.location); city.setText(cityBundle.getString("CityName")); }

编辑2：

确定向标签提供意图时也存在问题。您没有包含selectedCityBundle。由于您不必要地使用了太多的捆绑包，请参阅下面的代码MainActivity：

public class MainActivity extends TabActivity { private static TabHost tabHost; public static String selectedCity; @Override public void onCreate(Bundle savedInstanceState) { super.onCreate(savedInstanceState); setContentView(R.layout.activity_main); Resources res = getResources(); tabHost = getTabHost(); TabHost.TabSpec spec; Intent intent; intent= new Intent().setClass(this, A.class); intent.putExtra("CityName", "LA"); spec = tabHost.newTabSpec("tab1") .setIndicator("A", res.getDrawable(R.drawable.start)) .setContent(intent); tabHost.addTab(spec); intent = new Intent().setClass(this, B.class); intent.putExtra("CityName", "LA"); spec = tabHost.newTabSpec("tab2") .setIndicator("B", res.getDrawable(R.drawable.weather)) .setContent(intent); tabHost.addTab(spec); tabHost.setCurrentTab(0); }

请注意，我不确定意图和规格是否可以像这样重复使用。如果在更改选项卡时发现任何错误，请尝试为每个选项卡的不同变量创建新的意图和规范。

Answer 2

试试这个......

  Bundle bundle = getIntent().getExtras();
    String string = bundle.getString("CityName");
 city.setText(string);

通过选项卡中的Bundle传输变量

2 个答案: