0

我是新的 Android 编码器，我正在使用 startActivityForResult 函数。当我单击启动此方法的按钮时，我无法进入另一个活动，因为它崩溃了：

所以有 MainActivity.java 类。在 public void setRegisterOnClick(View v) 中，我想使用 startActivityForResult 两次，将其他意图发送到同一活动。Intents 包含传递给 Users.class 并用于声明 giveResponse 的 int 编号。但是每次我单击按钮启动 startActivityForResult 我的应用程序崩溃。

package com.example.login;

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

public class MainActivity extends Activity {

    private static final int USERS_REQUEST_CODE=1;
    private static String sActualLogin = "admin";
    private static String sActualPassword = "qwerty";
    private static String sContainer = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
    }

    @Override
    public boolean onCreateOptionsMenu(Menu menu) {
        // Inflate the menu; this adds items to the action bar if it is present.
        getMenuInflater().inflate(R.menu.main, menu);
        return true;
    }

    public void setLoginOnClick(View v)
    {
        EditText etLogin = (EditText) findViewById(R.id.tfLogin);
        EditText etPassword = (EditText) findViewById(R.id.tfPassword);

        String sLogin = etLogin.getText().toString();
        String sPassword = etPassword.getText().toString();

        if (sLogin.equals(sActualLogin) && sPassword.equals(sActualPassword))
        {
            Intent intent = new Intent (this, Inside.class);
            startActivity(intent);
        }
        else
        {
            Toast.makeText(this, "Invalid username or password.", Toast.LENGTH_LONG).show();
        }

    }

    public void setRegisterOnClick(View v)
    {
        Intent intentLOGIN = new Intent(this, Users.class);
        intentLOGIN.putExtra("Type",1);
        startActivityForResult(intentLOGIN, USERS_REQUEST_CODE);
        sActualLogin=sContainer;

        Intent intentPASSWORD= new Intent(this, Users.class);
        intentPASSWORD.putExtra("Type",2);
        startActivityForResult(intentPASSWORD, USERS_REQUEST_CODE);
        sActualPassword=sContainer;
    }

    protected void onActivityResult(int requestCode, int resultCode, Intent data) {
            super.onActivityResult(requestCode, resultCode, data);
            sContainer = data.getStringExtra(Users.RESPONSE);
        }    
}

用户类

package com.example.login;

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

public class Users extends Activity {

    public static final String RESPONSE = "Response";

    EditText etNewLogin = (EditText) findViewById(R.id.etChangeLogin);
    EditText etNewPassword = (EditText) findViewById(R.id.etChangePassword);

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.users);
    }

    public void giveResponse(View v)
    {   
        Intent intent = getIntent();
        int iOperation = intent.getIntExtra("Type", 0);


        if (iOperation == 1){
             String sNewLogin = etNewLogin.getText().toString();    
             Intent resultIntent1 = new Intent();
             resultIntent1.putExtra(RESPONSE, sNewLogin); 
             setResult(RESULT_OK, resultIntent1);
             finish();
        }

        if (iOperation == 2){
             String sNewPassword = etNewPassword.getText().toString();
             Intent resultIntent2 = new Intent();
             resultIntent2.putExtra(RESPONSE, sNewPassword);    
             setResult(RESULT_OK, resultIntent2);
             finish();
    }


    }
}

清单片段：

 <application
        android:allowBackup="true"
        android:icon="@drawable/ic_launcher"
        android:label="@string/app_name"
        android:theme="@style/AppTheme" >

        <activity
            android:name="com.example.login.MainActivity"
            android:label="@string/app_name" >
            <intent-filter>
                <action android:name="android.intent.action.MAIN" />

                <category android:name="android.intent.category.LAUNCHER" />
            </intent-filter>
        </activity>

        <activity android:name="com.example.login.Users"></activity>
        <activity android:name="com.example.login.Inside"></activity>

    </application>

错误：

05-12 20:22:10.350: W/dalvikvm(6349): threadid=1: thread exiting with uncaught exception (group=0x40a191f8)
05-12 20:22:10.360: E/AndroidRuntime(6349): FATAL EXCEPTION: main
05-12 20:22:10.360: E/AndroidRuntime(6349): java.lang.RuntimeException: Unable to instantiate activity ComponentInfo{com.example.login/com.example.login.Users}: java.lang.NullPointerException
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1880)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:1981)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.app.ActivityThread.access$600(ActivityThread.java:123)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1147)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.os.Handler.dispatchMessage(Handler.java:99)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.os.Looper.loop(Looper.java:137)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.app.ActivityThread.main(ActivityThread.java:4429)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at java.lang.reflect.Method.invokeNative(Native Method)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at java.lang.reflect.Method.invoke(Method.java:511)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:795)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:562)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at dalvik.system.NativeStart.main(Native Method)
05-12 20:22:10.360: E/AndroidRuntime(6349): Caused by: java.lang.NullPointerException
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.app.Activity.findViewById(Activity.java:1794)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at com.example.login.Users.<init>(Users.java:13)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at java.lang.Class.newInstanceImpl(Native Method)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at java.lang.Class.newInstance(Class.java:1319)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.app.Instrumentation.newActivity(Instrumentation.java:1023)
05-12 20:22:10.360: E/AndroidRuntime(6349):     at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:1871)
05-12 20:22:10.360: E/AndroidRuntime(6349):     ... 11 more

好吧，我为这种微不足道的问题写了很多（我猜是：P），但是由于我没有经验，因此需要花费数小时来解决它，但我仍然不明白。请指导/帮助我。

4

3 回答 3

2

您必须在layout使用setContentView访问子小部件之前设置使用findViewByID

例如

private EditText etNewLogin;
private EditText etNewPassword;


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.users);
    tNewLogin = (EditText) findViewById(R.id.etChangeLogin);
    tNewPassword = (EditText) findViewById(R.id.etChangePassword);
}

还要确保您使用正确的 ID 访问视图

于 2013-05-12T18:40:19.833 回答
1 
EditText etNewLogin;
EditText etNewPassword;;  
@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.users);
    etNewLogin = (EditText) findViewById(R.id.etChangeLogin);
    etNewPassword = (EditText) findViewById(R.id.etChangePassword);    
}

将内容设置为活动后，您需要找到id。

同样在 MainActivity 的 setLoginOnClick

    Intent intent = new Intent (MainActivity.this, Inside.class);// use activity context
    startActivity(intent);

相同的

    Toast.makeText(MainActivit.this, "Invalid username or password.", Toast.LENGTH_LONG).show();
    Intent intentLOGIN = new Intent(MainActivity.this, Users.class);// use activity context
    intentLOGIN.putExtra("Type",1);
    startActivityForResult(intentLOGIN, USERS_REQUEST_CODE);
    sActualLogin=sContainer;

    Intent intentPASSWORD= new Intent(MainActivity.this, Users.class);// use activity context
    intentPASSWORD.putExtra("Type",2);
    startActivityForResult(intentPASSWORD, USERS_REQUEST_CODE);
    sActualPassword=sContainer;
于 2013-05-12T18:47:50.127 回答
0

当您没有在 AndroidManifest 文件中正确声明活动时，通常会发生这种情况，请确保目录信息正确，以便您的应用可以找到您要访问的活动！

于 2014-09-26T05:54:34.873 回答