Question

我有一个Android程序，在点击按钮后发送到另一个活动。主要是，我想在新窗口中设置文本视图中的文本，使其对应于所选按钮。例如，如果我单击按钮编写器，则下一个新活动应该有一个文本视图，其中显示单词Writers。一切正常，除非我尝试在类别的TextView图标上设置文本。我也尝试在第一个活动中调用此更改，在启动第二个活动之前，它不起作用。我还提到如果我用setText注释该行，程序就可以正常工作。

private String          category;
public final static String CATEGORY_MESSAGE = "e.c.project.CATEGORY";
public void onClick(View v) {
    switch(v.getId())
        {
            case R.id.actors:
                category = "actors";
                playTheGame(v);
            break;
            case R.id.cartoons:
                category = "cartoons";
                playTheGame(v);
        break;
            case R.id.singers:
                category = "singers";
                playTheGame(v);
            break;
            case R.id.writers:
                category = "writers";
                playTheGame(v);
            break;
        }
    }

    public void playTheGame( View view ){
        Intent intent = new Intent(this, PlayGame.class);
        String category = playGameButton.getText().toString();
        intent.putExtra(CATEGORY_MESSAGE, category);
//      TextView tv = (TextView) findViewById(R.id.categoryTV);
//      tv.setText(category);
        startActivity(intent);
    }

这是来自第二个活动的OnCreate方法：

    private TextView            categoryTV;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    Intent intent = getIntent();
    String category = intent.getStringExtra(GameCategories.CATEGORY_MESSAGE);

    categoryTV = (TextView) findViewById(R.id.categoryTV);
    categoryTV.setText(category);

    setContentView(R.layout.activity_play_game);
    // Show the Up button in the action bar.
    setupActionBar();
}

Answer 1

您需要在setContentView(R.layout.activity_play_game);之前致电categoryTV = (TextView) findViewById(R.id.categoryTV);，否则TextView为null

   private TextView, categoryTV;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
       setContentView(R.layout.activity_play_game);  // make this call BEFORE initializing ANY views
       Intent intent = getIntent();
       String category = intent.getStringExtra(GameCategories.CATEGORY_MESSAGE);

       categoryTV = (TextView) findViewById(R.id.categoryTV);
       categoryTV.setText(category);


        // Show the Up button in the action bar.
         setupActionBar();
    }

View中存在Layout，因此如果您在Layout，setContentView()或inflater充气之前尝试访问其中任何一个，当您尝试在null

上调用方法时，它们将NPE生成setText()

Android应用程序在TextView上的setText之后停止

1 个答案: