为什么我出现NullPointerException? [英] Why i got NullPointerException ?

问题描述

代码已建立好:

Code builded ok:

Button buttonCancel = (Button)findViewById(R.id.Cancel);
try{
buttonCancel.setOnClickListener(buttonCancelOnClickListener);
}catch(Exception x)
{
    x.toString();//NullPointerException
}

在text_enter.xml中:

In text_enter.xml:

<Button
    android:id="@+id/Cancel"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignBaseline="@+id/SendText"
    android:layout_alignBottom="@+id/SendText"
    android:layout_alignParentLeft="true"
    android:text="Cancel" />

buttonCancel = null，为什么?请帮助.

buttonCancel = null, why? Please, help.

推荐答案

尽管您没有提供足够的信息，但可以尝试这样做.

Though you not provide enough information but you can try like this..

private Button buttonCancle;
@Override
public void onCreate(Bundle savedInstanceState)
{
    super.onCreate(savedInstanceState);
    setContentView(R.layout.wishingpage);

    buttonCancel = (Button)findViewById(R.id.Cancel);

    buttonCancel.setOnClickListener(this);
    }

public void onClick(View v) {
    // TODO Auto-generated method stub
    switch (v.getId()) {
    case R.id.buttonCancel:
             //do your button work here..you can add more button event using case
        break;
            }
    }

已解决.我必须

setContentView(R.layout.text_enter);

在声明并设置它的侦听器之前，其中包含我的取消"按钮.

that contains my Cancel button, before declaring and setting listener for it.

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