嘗試覆蓋其他類的TextView中的文本時，Android應用程序崩潰

Question

我嘗試在一個名為UserProfile（）的類中更改3個textviews，該類從類UpdateProfile（）調用方法update（），該類UserProfile做如下事情：

package com.safm;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.TextView;

public class UserProfile extends Activity {
TextView username, usersurname, useremail;

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

    username = (TextView) findViewById(R.id.username);
    usersurname = (TextView) findViewById(R.id.usersurname);
    useremail = (TextView) findViewById(R.id.useremail);
}

public void updateButton(View view){
    Intent i = new Intent(this, UpdateProfile.class);
    startActivity(i);
}

public void update(String nname, String nusername, String nemail){
    System.out.println("2");
    System.out.println(nname);
    username.setText(nname);
    usersurname.setText(nusername);
    useremail.setText(nemail);
    System.out.println("3");
}

}

updateButton方法調用UpdateProfile類：

package com.safm;

import android.app.Activity;
import android.content.Intent;
import android.os.Bundle;
import android.view.View;
import android.widget.EditText;
import android.widget.Toast;

public class UpdateProfile extends Activity {
EditText newusernametxt, newsurnametxt, newemailtxt;

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

    newusernametxt = (EditText) findViewById(R.id.newusernametxt);
    newsurnametxt = (EditText) findViewById(R.id.newsurnametxt );
    newemailtxt = (EditText) findViewById(R.id.newemailtxt );
}

public void updateInfo(View view){      
    String nname = newusernametxt .getText().toString();
    String nsurname = newsurnametxt .getText().toString();
    String nemail = newemailtxt .getText().toString();

    if(nname.compareTo("") != 0 && nsurname.compareTo("") != 0 && nemail.compareTo("") != 0){           
        UserProfile profile = new UserProfile();
        System.out.println("1");

        profile.update(nname, nsurname, nemail);
        System.out.println("4");

        Toast.makeText(this, "Success, the profile has been updated", Toast.LENGTH_SHORT).show();
    }else{
        Toast.makeText(this, "You can't empty fields", Toast.LENGTH_SHORT).show();
    }

}

如您所見，這是我的logcat文件，前2個標志正確打印​​，錯誤是當我嘗試在TextView上設置另一個文本時，但是字符串（nname，nsurname和nemail）的值不為空也打印在控制台幫助中！

    05-14 21:43:31.140: I/System.out(878): 1
    05-14 21:43:31.140: I/System.out(878): 2
    05-14 21:43:31.150: I/System.out(878): TextEditValue

    05-14 21:43:31.150: D/AndroidRuntime(878): Shutting down VM
    05-14 21:43:31.150: W/dalvikvm(878): threadid=1: thread exiting with uncaught exception (group=0x40a71930)
    05-14 21:43:31.310: E/AndroidRuntime(878): FATAL EXCEPTION: main
    05-14 21:43:31.310: E/AndroidRuntime(878): java.lang.IllegalStateException: Could not execute method of the activity
    05-14 21:43:31.310: E/AndroidRuntime(878):  at android.view.View$1.onClick(View.java:3599)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at android.view.View.performClick(View.java:4204)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at android.view.View$PerformClick.run(View.java:17355)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at android.os.Handler.handleCallback(Handler.java:725)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at android.os.Handler.dispatchMessage(Handler.java:92)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at android.os.Looper.loop(Looper.java:137)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at android.app.ActivityThread.main(ActivityThread.java:5041)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at java.lang.reflect.Method.invokeNative(Native Method)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at java.lang.reflect.Method.invoke(Method.java:511)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:793)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:560)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at dalvik.system.NativeStart.main(Native Method)
    05-14 21:43:31.310: E/AndroidRuntime(878): Caused by: java.lang.reflect.InvocationTargetException
    05-14 21:43:31.310: E/AndroidRuntime(878):  at java.lang.reflect.Method.invokeNative(Native Method)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at java.lang.reflect.Method.invoke(Method.java:511)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at android.view.View$1.onClick(View.java:3594)
    05-14 21:43:31.310: E/AndroidRuntime(878):  ... 11 more
    05-14 21:43:31.310: E/AndroidRuntime(878): Caused by: java.lang.NullPointerException
    05-14 21:43:31.310: E/AndroidRuntime(878):  at com.safm.UserProfile.update(UserProfile.java:31)
    05-14 21:43:31.310: E/AndroidRuntime(878):  at com.safm.UserProfile.updateInfo(UpdateProfile.java:33)
    05-14 21:43:31.310: E/AndroidRuntime(878):  ... 14 more

注意：我已經清理了項目，並在onCreate方法之外定義了ProfileUser類中的TextView和UpdateProfile中的TextEdit，但是不起作用。

謝謝。

Answer 1

Android中的活動是單獨的容器，絕不允許彼此直接接觸。 這是因為Android后面的應用程序堆棧會在活動不再處於前台時“凍結”活動，甚至可以根據操作系統的判斷將其交換到硬存儲上以節省RAM。

您的UserProfile封裝應該只是在UpdateProfile活動關閉后重新加載其數據，或者通過startActivityForResult請求以正確的方式進行通信。

從各個角度看，當前的實現在技術上都是不正確的，因為您正在對UpdateProfile活動進行硬編碼，以便始終從UserProfile活動中調用它。 如果有一天您引入了一個新的菜單選項以直接從主屏幕調用該怎么辦？ 活動始終是分開的，不應進行此類假設。