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设置onActivityResult后的文本查看文本

android-lifecycle android java

michasaucer · 技术社区 · 7 年前

我有一个带有登录页面的应用程序。

首先,我有我的 MainActivity

public class MainActivity extends AppCompatActivity {

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

    // here i launch LoginActivity
    startActivityForResult(new Intent(this, LoginActivity.class), REQUEST_CODE);

    emailText = findViewById(R.id.nav_text_email);
    usernameText = findViewById(R.id.nav_text_username);
}

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data){
    if(requestCode == REQUEST_CODE){
        if(resultCode != Activity.RESULT_OK) {
            finish();
        }
        // if login succesful, i attach to variable instance of
        // logged user class.
        // that part works correct, in object vars exist
        loggedUser = loggedUser.getInstance();

        // i want to attach strings after succesful login
        emailText.setText(loggedUser.getEmail());
        usernameText.setText(loggedUser.getUsername());
    }
}

使用上述代码运行应用程序时,成功后 LoginActivity

2019-01-26 20:46:48.015 13071-13071/com.example.admin.keystroke_dynamics E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.admin.keystroke_dynamics, PID: 13071
java.lang.RuntimeException: Unable to resume activity {com.example.admin.keystroke_dynamics/com.example.admin.keystroke_dynamics.Activities.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3586)
    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3626)
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2876)
    at android.app.ActivityThread.-wrap12(ActivityThread.java)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:156)
    at android.app.ActivityThread.main(ActivityThread.java:6523)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.example.admin.keystroke_dynamics.Activities.MainActivity.onResume(MainActivity.java:89)
    at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1279)
    at android.app.Activity.performResume(Activity.java:7022)
    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3561)
    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3626)Â 
    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2876)Â 
    at android.app.ActivityThread.-wrap12(ActivityThread.java)Â 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1567)Â 
    at android.os.Handler.dispatchMessage(Handler.java:105)Â 
    at android.os.Looper.loop(Looper.java:156)Â 
    at android.app.ActivityThread.main(ActivityThread.java:6523)Â 
    at java.lang.reflect.Method.invoke(Native Method)Â 
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)Â 
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)Â

当我删除 setText() 从`onActivityResult()中,我没有得到该异常。当我单击登录按钮,应用程序崩溃。

setText()

我的问题是,如何设置文本 textviews

使现代化

即使我把线插进去 loggedUser loggedUser = loggedUser.getInstance() 搬家到 onCreat ,我仍然得到那个NPE。

编辑:

onResume

@Override
protected void onResume()
{
    if(isLogged) {
        emailText.setText(loggedUser.getEmail());
        usernameText.setText(loggedUser.getUsername());
    }
    super.onResume();
}

编辑 onActivityResult() :

@Override
public void onActivityResult(int requestCode, int resultCode, Intent data){
    if(requestCode == REQUEST_CODE){
        if(resultCode != Activity.RESULT_OK) {
            finish();
        }
        isLogged = true; //var for if statement in onResume()
        loggedUser = loggedUser.getInstance();
    }
}

但我还是会犯同样的错误 onResume() 方法设置时使用 TextViews

2019-01-26 21:21:57.752 18262-18262/com.example.admin.keystroke_dynamics E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.example.admin.keystroke_dynamics, PID: 18262
java.lang.RuntimeException: Unable to resume activity {com.example.admin.keystroke_dynamics/com.example.admin.keystroke_dynamics.Activities.MainActivity}: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3586)
    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3626)
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1618)
    at android.os.Handler.dispatchMessage(Handler.java:105)
    at android.os.Looper.loop(Looper.java:156)
    at android.app.ActivityThread.main(ActivityThread.java:6523)
    at java.lang.reflect.Method.invoke(Native Method)
    at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:942)
    at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:832)
 Caused by: java.lang.NullPointerException: Attempt to invoke virtual method 'void android.widget.TextView.setText(java.lang.CharSequence)' on a null object reference
    at com.example.admin.keystroke_dynamics.Activities.MainActivity.onResume(MainActivity.java:90)
    at android.app.Instrumentation.callActivityOnResume(Instrumentation.java:1279)
    at android.app.Activity.performResume(Activity.java:7022)
    at android.app.ActivityThread.performResumeActivity(ActivityThread.java:3561)
    at android.app.ActivityThread.handleResumeActivity(ActivityThread.java:3626)Â 
    at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1618)Â 
    at android.os.Handler.dispatchMessage(Handler.java:105)Â 
    at android.os.Looper.loop(Looper.java:156)Â 
    at android.app.ActivityThread.main(ActivityThread.java:6523)

3 回复 | 直到 7 年前

Greg Moens 7 年前

如果您使用的是更复杂的布局,则onCreate()中也可能没有完整内容视图。如果在onCreate()中发现视图为空,请尝试将findViewById()移动到生命周期中的稍后点。

Charan M 7 年前

试着像这样重新排列代码

emailText = findViewById(R.id.nav_text_email);
usernameText = findViewById(R.id.nav_text_username);
startActivityForResult(new Intent(this, LoginActivity.class), REQUEST_CODE);

christoandrew 7 年前

public class MainActivity extends AppCompatActivity {
TextView emailText;
TextView usernameText;
@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.main_activity);

    // here i launch LoginActivity
    startActivityForResult(new Intent(this, LoginActivity.class), REQUEST_CODE);

    emailText = findViewById(R.id.nav_text_email);
    usernameText = findViewById(R.id.nav_text_username);
}

可以发表评论吗

使现代化

NavigationView navigationView = findViewById(R.id.nav_id)
View header = navigationView.getHeaderView(0)
TextView usernameText = header.findViewById(R.id.username_text_view_id);