Android：使用按鈕點擊意圖啟動活動

Question

我正在嘗試使用intent啟動activitiy：

    public class Bez_provjere_739 extends Activity { 
Button Tbutun;
 public void onCreate(Bundle savedInstanceState) {

    Tbutun.setOnClickListener(new OnClickListener() {

        public void onClick(View v) {
            // TODO Auto-generated method stub

            Intent otvoriIn = new Intent("com.riteh.HL.IN");

            startActivity(otvoriIn);
        }
    });

我以相同的方式在我的應用程序中多次使用它，但僅在這種情況下我得到錯誤：

05-17 00：44：43.694：E / AndroidRuntime（3533）：java.lang.RuntimeException：無法啟動活動ComponentInfo {com.riteh.HL / com.riteh.HL.Bez_provjere_739}：java.lang.NullPointerException

Answer 1

您從未初始化按鈕也未分配給它，因此它為空。

此外，您的代碼中缺少一些基礎知識：

// naming conventions - variable names start with lower case letter
private Button tbutun; 

@Override
public void onCreate(Bundle savedInstanceState) {
    // always call super.onCreate
    super.onCreate(savedInstanceState);
    // if you have a layout XML, use it
    setContentView(R.layout.lay_xml_name);
    // if the button declared in the layout, refer to it
    tbutun = (Button)findViewById(R.id.the_button_name);
    // the rest
}

Answer 2

初始化你的按鈕，試試這個

  public class Bez_provjere_739 extends Activity { 
    Button Tbutun;
     public void onCreate(Bundle savedInstanceState) {
    setContentView(R.layout.main);

    Tbutun=(Button)findViewById(R.id.button1) //change the id as per yours

        Tbutun.setOnClickListener(new OnClickListener() {

            public void onClick(View v) {
                // TODO Auto-generated method stub

                Intent otvoriIn = new Intent("com.riteh.HL.IN");

                startActivity(otvoriIn);
            }
        });