Can't resolve symbol 'setText' error

问题:

like the title says I'm getting an error when trying to set a text view text from java in my android project, I can't see why.

    package com.codeherenow.sicalculator;

    import android.app.Activity;
    import android.os.Bundle;
    import android.widget.TextView;
    import android.widget.SeekBar;

    public class SICalculatorActivity extends Activity implements SeekBar.OnSeekBarChangeListener{
public double years;
public TextView YT = (TextView) findViewById(R.id.Years);

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.sicalculator);
}
    @Override
    public void onProgressChanged (SeekBar seekBar,int i, boolean b){
        years = i;
    }

    @Override
    public void onStartTrackingTouch (SeekBar seekBar){

    }

    @Override
    public void onStopTrackingTouch (SeekBar seekBar){

    }
YT.setText(years + " Year(s)");

}

回答1:

You've got a couple issues.

First, you can't do this here

public TextView YT = (TextView) findViewById(R.id.Years);

Because the layout hasn't been inflated yet so you can't look for your View witht findViewById(). You can declare it there

public TextView YT;

but you need to initialize it after you call setContentVie()

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

    //can't do it before that line ^
    YT = (TextView) findViewById(R.id.Years);
}

And you are trying to call setText() outside of a method. Move that to some method. But you can't do it in onCreate() because Years isn't given a value. So you probably want it somewhere else. Maybe in onProgressChanged().

Also, to follow Java naming conventions, you should name your variables by starting with lower case (yt or yT and years).

回答2:

Example XML

<TextView
    android:id="@+id/myAwesomeTextView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_alignParentTop="true"
    android:text="Escriba el mensaje y luego clickee el canal a ser enviado"
    android:textSize="20sp" />

example activity class

//in your OnCreate() method
TextView myAwesomeTextView = (TextView)findViewById(R.id.myAwesomeTextView);
myAwesomeTextView.setText("My Awesome Text");

So you need to add

YT = (TextView) findViewById(R.id.Years); 

inside onCreate method

回答3:

This YT = (TextView) findViewById(R.id.Years); and YT.setText(years + " Year(s)"); must be moved into the onCreate() method

So, leave this

public TextView YT;

And initialize it here:

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

    YT = (TextView) findViewById(R.id.Years);
    YT.setText(years + " Year(s)");
}

[EDIT]

If you want a dynamic change with the progress value:

@Override
public void onProgressChanged (SeekBar seekBar,int i, boolean b)
{
    //years = i;
    YT.setText(i + " Year(s)");
}

回答4:

public TextView YT = (TextView) findViewById(R.id.Years);

statement must write onCreate() method.