Question

这是第二个活动OnCreate

中的代码

final Button arrayBtn = (Button) findViewById(buttonQtyID[i]);
            arrayBtn.setOnClickListener(new View.OnClickListener() {
                public void onClick(View v) {
                    ClearQtyBtnColor(); 
                    arrayBtn.getBackground().setColorFilter(0xffff9999, PorterDuff.Mode.MULTIPLY);
                    MainActivity  cls2= new MainActivity();

                    String Price = cls2.CheckUnitPrice("NORMAL"); // ERROR AT HERE
                    TextView view = (TextView) findViewById(R.id.Harga_lblPrice);
                    //view.setText((Double.parseDouble(Price) * Integer.parseInt(arrayBtn.getText().toString()))+"");
                }
             });

这是主要活动中的编码

public Cursor DB_GetUnitPrice(){
    DataBaseHelper myDbHelper = new DataBaseHelper(this.getApplicationContext());
    myDbHelper = new DataBaseHelper(this);
    try { 
    myDbHelper.createDataBase();  
    } catch (IOException ioe) { 
    throw new Error("Unable to create database"); 
    }  
    try {  
    myDbHelper.openDataBase();         
    }catch(SQLException sqle){  
    throw sqle;  
    }
    SQLiteDatabase db = myDbHelper.getReadableDatabase();

    String Insert_Data="Select Normal_Rate,Discounted_Rate FROM Tbl_Rate WHERE Route_ID="+global.Route_ID+" AND ((From_LocationID="+global.From_LocationID+" AND To_LocationID="+global.To_LocationID+") OR (From_LocationID="+global.To_LocationID+" AND To_LocationID="+global.From_LocationID + "))";
    Cursor c = db.rawQuery(Insert_Data, null);

    //c.close(); // cannot will error
    //db.close(); // cannot will error
    //myDbHelper.close();
    return c;
}

public String CheckUnitPrice(String PriceType){
    if ((global.To_LocationID != 0) && (global.From_LocationID != 0)) {
            Cursor c = DB_GetUnitPrice();
            double Normal_Rate = 0;
            double Discounted_Rate = 0;
            while (c.moveToNext()) {
                Normal_Rate = c.getDouble(c.getColumnIndex("Normal_Rate"));
                Discounted_Rate = c.getDouble(c.getColumnIndex("Discounted_Rate"));
            }
            if (PriceType.equalsIgnoreCase("NORMAL")){
                return String.format("%.2f",(Normal_Rate));
            }else{
                return String.format("%.2f",(Discounted_Rate));
            }
    }else{
        return "0.00";
    }
}

这是我在全局类

中的全局变量声明

public class Global extends Application {
    String Driver_Code;
    String Driver_Name;
    long Driver_ID;

    long Vehicle_ID;
    String Plat_No;

    long Route_ID;

    int From_LocationID;
    int To_LocationID;
    String From_LocationName;
    String To_LocationName;
    int From_Tag;
    int To_Tag;

}

这是Log cat错误日志

12-02 14:13:48.718: E/AndroidRuntime(10643): FATAL EXCEPTION: main
12-02 14:13:48.718: E/AndroidRuntime(10643): java.lang.NullPointerException
12-02 14:13:48.718: E/AndroidRuntime(10643):    at com.example.abc2.MainActivity.CheckUnitPrice(MainActivity.java:246)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at com.example.abc2.SecondActivity$2.onClick(SecondActivity.java:58)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at android.view.View.performClick(View.java:2485)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at android.view.View$PerformClick.run(View.java:9080)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at android.os.Handler.handleCallback(Handler.java:587)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at android.os.Handler.dispatchMessage(Handler.java:92)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at android.os.Looper.loop(Looper.java:123)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at android.app.ActivityThread.main(ActivityThread.java:3647)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at java.lang.reflect.Method.invokeNative(Native Method)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at java.lang.reflect.Method.invoke(Method.java:507)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:839)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:597)
12-02 14:13:48.718: E/AndroidRuntime(10643):    at dalvik.system.NativeStart.main(Native Method)

在Main活动上调用CheckUnitPrice工作正常，可以从Sqlite返回Price，但是当从另一个活动调用时，会出现问题。请帮忙

Answer 1

您应该将Global类中的变量设置为public，并从ApplicationContext获取对该类的访问权。

Global state = ((Global) getApplicationContext());
int value = state.To_LocationID

此外，在application标记下的清单文件中输入一个条目，让系统知道您的应用程序类。

android:name="Global"

注意：您应该将Global中的成员变量设为私有，并为这些变量生成getters and setters。避免直接访问变量。

Answer 2

如果MainActivity类扩展了Activity，则无法使用此构造：

MainActivity  cls2= new MainActivity();

创建简单类并在其中创建静态方法。

Answer 3

试试这个......你需要给变量public static，然后才能得到那个变量

public class Global extends Application {
    public static String Driver_Code;
    public static String Driver_Name;
    public static long Driver_ID;

    public static long Vehicle_ID;
    public static String Plat_No;

    public static long Route_ID;

    public static int From_LocationID;
    public static int To_LocationID;
    public static String From_LocationName;
    public static String To_LocationName;
    public static int From_Tag;
    public static int To_Tag;

}

您可以访问以下变量..

if ((Global.To_LocationID != 0) && (Global.From_LocationID != 0)) {

第二个活动调用主要活动功能在Android中崩溃

3 个答案: