Question

这是我动态添加按钮的代码。运行时抛出错误。任何的想法？ :)

DatabaseHandler db;
private RelativeLayout relativeLayout;

@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_settings);
    boolean userCounts = db.getUserExistance();
    if(userCounts == false){            
        Button button= new Button(this);
        button.setText("Add password");
        relativeLayout.addView(button);
    }
    else if(userCounts == true){            
        Button button2 = new Button(this);
        button2.setText("Change password");
        relativeLayout.addView(button2);            
    }

}

错误日志：

09-17 11:44:34.658: D/AndroidRuntime(655): Shutting down VM 09-17 11:44:34.658: W/dalvikvm(655): threadid=1: thread exiting with uncaught exception (group=0x40a13300)
09-17 11:44:34.699: E/AndroidRuntime(655): FATAL EXCEPTION: main 
09-17 11:44:34.699: E/AndroidRuntime(655): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.projects.myworldsafe/com.projects.myworldsafe.Settings}: java.lang.NullPointerException 
09-17 11:44:34.699: E/AndroidRuntime(655): at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2059)

Answer 1

您尚未初始化relativeLayout。如果您以编程方式设置relativeLayout，请尝试：

relativeLayout = new RelativeLayout(this);

如果它首先在您的布局文件中，您需要找到它，例如：

relativeLayout = (RelativeLayout) this.findViewById(R.id.your_layout_id);

与DatabaseHandler db

相同

Answer 2

我认为您在首次使用之前忘记初始化{{1and1}}。

Answer 3

据我所知，你需要给出Relative layout

的布局

RelativeLayout = (RelativeLayout) this.findViewById(R.id.relativeID);

Answer 4

试试这个，

DatabaseHandler db;
    private RelativeLayout relativeLayout;

    @Override
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_settings);
        boolean userCounts = db.getUserExistance();
        relativeLayout = (RelativeLayout) this.findViewById(R.id.myRelativeLayout);
        if(userCounts == false){            
            Button button= new Button(this);
            button.setText("Add password");
            relativeLayout.addView(button);
        }
        else if(userCounts == true){            
            Button button2 = new Button(this);
            button2.setText("Change password");
            relativeLayout.addView(button2);            
        }

    }

这有什么问题？这是投掷错误

4 个答案: